Service size from the load calculation, not the nameplates
“You need 200 A” is sometimes a diagnosis and sometimes an upsell. This tool runs a simplified optional calculation so you can tell which. It is not the load calculation an electrician stamps, and it is not a reason to open a panel yourself.
NEC 220.82shape, not a stamp100% of the first 10 kVA of general load, 40% of the remainder, HVAC at 100%, EVSE at 125% as a continuous load. Your jurisdiction adopts an edition of the NEC. This page does not declare your house illegal.
Enter floor area, nameplate VA for range, dryer, water heater and HVAC, optional EV amps, and the existing service size if you know it. The output is an ampere figure at 240 V and whether that figure overshoots the existing service on these inputs. Live work is not DIY. HyreElectrical does not perform electrical work.
Nameplates in, amps out
Not a stamp. Nothing is emailed. Do not open the panel to read this.
A simplified optional calculation, not a stamped load calc. Live work is not DIY. HyreElectrical does not perform electrical work.
Adding up the nameplates is the wrong arithmetic, and the Code says so itself
Almost every homeowner who works out their own service size does it by adding the numbers printed on their appliances. That produces a figure far larger than the one an electrician calculates, and the difference is not a rounding error. It is a deliberate feature of the method.
Start with what a nameplate is. The plate on the back of a range states what that appliance draws with everything in it running at once — every element, the oven, the broiler.
It is a statement about the appliance in its worst moment, made by the manufacturer, and it has to be, because that is the moment the wiring to it must survive.
Now add the plates up. Range, dryer, water heater, air conditioner, dishwasher, disposal, plus the lighting and receptacle allowance for the floor area.
On the worked example below that sum comes to about 39,100 volt-amperes, which at 240 V is roughly 163 amperes.
A homeowner who does that arithmetic concludes their 100 A service is hopelessly undersized, and a salesperson who does it in front of them is not lying about the addition.
The addition is right and the conclusion is wrong, because that sum describes a house in which the oven, the broiler, the dryer, the water heater and the air conditioner are all at full draw in the same instant, and nobody lives in that house.
The Code does not require the service to be sized for it either.
What the Code actually permits. NEC 220.82 says it plainly: “It shall be permissible to calculate the feeder and service loads in accordance with this section instead of the method specified in Part III of this article.”
The optional calculation exists precisely because the sum of the nameplates is a poor description of a dwelling, and it replaces that sum with demand factors.
Why this matters commercially. "Your panel is too small" is the opening line of an expensive job. Sometimes it is entirely true — an old 60 A service with a heat pump proposal in front of it usually is.
But a homeowner who cannot tell the difference between a nameplate sum and a calculated load has no way to test the claim, and a person who cannot test a claim tends to buy.
What this page is for. Not to overrule an electrician. To let you arrive at the conversation knowing which arithmetic is being done, and to be able to ask for the other one.
Nothing on this site is a stamped load calculation, a design, or a permit document. A load calculation that an inspector accepts is produced by someone who has seen the building and signs for it.
The four numbers the optional method actually runs on
Everything else in a residential load calculation is a nameplate you read off equipment. These four are the Code’s own, and they are the reason the answer comes out where it does.
10 kVAof general load counted at 100 percentNEC 220.82, 2014 edition
40%the factor applied to every volt-ampere of general load after thatNEC 220.82(B)
3 VA/ft²general lighting and general-use receptacle allowance by floor areaNEC 220.82(B)(1)
100 Athe minimum service disconnect rating for a one-family dwellingNEC 230.79(C)
Quoted from NFPA 70, National Electrical Code, Article 220 — Branch-Circuit, Feeder, and Service Calculations, 2014 edition, retrieved from a hosted copy on 2026-09-05. Adoption and amendment of the National Electrical Code is local.
A state or city may be on an older edition, may amend it, and may add rules of its own. Confirm the adopted edition and the amendments with the authority having jurisdiction before relying on any code figure here.
How the optional calculation runs, in the order it runs
Five steps. The third is the one that does all the work, and the fourth is the one everybody gets wrong by adding when they should be choosing.
1
Check that the house qualifies at all
NEC 220.82(A): “This section applies to a dwelling unit having the total connected load served by a single 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater.” A 60 A service falls outside it and goes to the standard calculation.
2
Build the general load from floor area, circuits and nameplates
The allowance is “3 volt-amperes/ft2 for general lighting and general-use receptacles”, plus “1500 volt-amperes for each 2-wire, 20-ampere small-appliance branch circuit and each laundry branch circuit”, plus the nameplate rating of the fastened-in-place appliances, ranges, ovens, dryers and water heaters.
And note what the floor area leaves out
“The calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use.” The garage you were counting does not count.
3
Apply the demand factor — this is the step that changes the answer
“The general calculated load shall be not less than 100 percent of the first 10 kVA plus 40 percent of the remainder of the following loads.” On the worked example, 34,100 VA of general load becomes 19,640 VA.
4
Add heating or cooling — the largest one, not all of them
NEC 220.82(C): “The largest of the following six selections (load in kVA) shall be included.” Six selections, and the word is largest. A heat pump and a separate air conditioner are not both counted; adding them inflates the answer toward more equipment.
5
Divide by the voltage and compare with the service
Volt-amperes divided by 240 gives amperes. On the worked example: 24,640 VA, or about 103 A. Compare that with the existing service rating — and then, before concluding anything, read the section below on what this comparison cannot see.
The worked example, line by line
A 2,000 sq ft dwelling with an electric range, an electric dryer, an electric water heater, a dishwasher, a disposal and central air. The last column is the useful one: it says what each line is doing to the answer, which is not obvious from the number.
Line
Volt-amperes
Where it comes from
What it is really doing
General lighting and receptacles
6,000
2,000 ft² × 3 VA/ft², per NEC 220.82(B)(1)
Standing in for every lamp, television, charger and vacuum cleaner in the house at once. It is an allowance, not a measurement, and it does not scale with how many gadgets you own.
Small-appliance branch circuits
3,000
Two circuits at 1,500 VA each
The kitchen counter circuits, counted whether or not anything is plugged into them. A second kitchen or an added counter circuit adds another 1,500 VA before any appliance exists.
Laundry circuit
1,500
1,500 VA, per NEC 220.82(B)(2)
The circuit, not the dryer. The dryer is its own line below, which is why a laundry room appears twice and neither entry is a mistake.
Range nameplate
12,000
Nameplate rating, per 220.82(B)(3)b
Here is the sting: under NEC Table 220.55, Column C a single range not over 12 kW would be taken as a 8 kW demand in the standard calculation. The optional method uses nameplate but then discounts the whole pile by 60 percent, arriving in the same neighborhood by a different road. How many US homes already cook on electricity, and how the count changes with the fuel scope, is electric range adoption.
Clothes dryer
5,000
NEC 220.54: “5000 watts (volt-amperes) or the nameplate rating, whichever is larger”
A floor, not a ceiling. A small dryer does not get counted small. This is one of the few places the Code rounds against you, and it is deliberate.
Electric water heater
4,500
Nameplate rating, per 220.82(B)(3)d
Zero if the water heater is gas — which is why a fuel-switching project changes a load calculation twice over: it removes a gas appliance and adds this line.
Dishwasher and disposal
2,100
Nameplate ratings, fastened in place
Small individually and invisible after the 40 percent factor. Chasing these is not where a load calculation is won or lost.
General load, before demand factors
34,100
Sum of the lines above
The number a homeowner stops at. It is not the answer and the Code never asks for it as one.
General demand, after 220.82(B)
19,640
10,000 VA at 100%, 24,100 VA at 40%
The single largest movement on the page. Roughly 14,460 VA disappears here, not because the appliances got smaller but because they do not all run at once.
Air conditioning
5,000
NEC 220.82(C)(1), nameplate at 100 percent
Undiscounted, because on the day it matters it genuinely is running continuously. Note that it is the largest of six selections, not the sum of them.
Calculated load
24,640 VA ≈ 103 A at 240 V
HyreElectrical calculation on the constants above
Against the raw nameplate sum of about 163 A. Same house, same appliances, two very different conversations with a contractor.
HyreElectrical calculation, performed on the Code constants quoted in the sources. It is a worked illustration of the method, not a load calculation for any real building, and it omits lines a real dwelling may carry.
Nothing on this site is a stamped load calculation, a design, or a permit document. A load calculation that an inspector accepts is produced by someone who has seen the building and signs for it.
The size of the gap, drawn
The demand factor is easy to nod along with and hard to feel. This is the same worked example as a picture: what the nameplates say, what the calculation says, and where the difference goes.
The fourth segment is the whole argument of this page. It is not capacity you are being denied — it is capacity the method has decided you will never draw simultaneously.Our arithmetic, on the demand factors quoted from NEC 220.82, 2014 edition.
Read the last segment as a risk decision, not a discount. The Code is not being generous.
It is codifying an observation about how dwellings behave, backed by a very long record of services sized this way not failing.
Diversity — the fact that loads do not coincide — is a real physical property of a household, not an accounting trick.
Which is also its limit. Diversity is an assumption about behavior, and behavior is changing. A house that heats with gas, cooks occasionally and parks a petrol car has enormous diversity.
A house with a heat pump running all evening, an induction hob, a heat pump water heater on a timer and a car charging overnight has noticeably less of it, because several of those loads are long, steady and overlapping rather than short and random.
That is the honest case for a service upgrade, and it is a much better argument than "your panel is old". If someone is recommending a larger service, the question worth asking is which of your new loads they expect to coincide, and for how long.
And the honest case against one is that the coincidence may be manageable rather than physical. The section on load management below is about exactly that.
The six heating-and-cooling selections, and why only one of them counts
NEC 220.82(C) lists six ways of describing a heating or cooling load and then instructs you to include the largest. Not the sum. The table is here because the difference between "largest" and "sum" can be several thousand volt-amperes, which is several tens of amperes, which is the difference between two service sizes.
Selection
Percentage
What it describes
When it is the largest
220.82(C)(1)
100%
The nameplate rating(s) of the air conditioning and cooling
A conventional split system in a cooling-dominated climate, where nothing electric heats the house.
220.82(C)(2)
100%
The nameplate rating(s) of the heat pump when the heat pump is used without any supplemental electric heating
A heat pump with no electric backup at all — increasingly common with cold-climate equipment, and the selection a good design tries to reach.
220.82(C)(3)
100%
The nameplate rating(s) of the heat pump compressor and 65 percent of the supplemental electric heating for central electric space-heating systems
A heat pump with electric strip backup, which is the usual retrofit. Note the 65 percent on the strips and the allowance where an interlock stops the compressor and the strips running together.
220.82(C)(4)
65%
The nameplate rating(s) of electric space heating if less than four separately controlled units
Resistance heating in a house with fewer than four separately controlled units — a small house on baseboards, typically.
220.82(C)(5)
40%
The nameplate rating(s) of electric space heating if four or more separately controlled units
Resistance heating spread across four or more thermostats, where the Code accepts that they will not all call at once.
220.82(C)(6)
100%
The nameplate ratings of electric thermal storage and other heating systems where the usual load is expected to be continuous at the full nameplate value
Thermal storage and anything else expected to sit at full nameplate continuously. The Code adds that a system qualifying here “shall not be calculated under any other selection”.
Quoted from NEC 220.82(C), NFPA 70, National Electrical Code, Article 220 — Branch-Circuit, Feeder, and Service Calculations, 2014 edition. The fourth column is our reading of when each selection dominates, not the Code’s statement. Adoption and amendment of the National Electrical Code is local.
A state or city may be on an older edition, may amend it, and may add rules of its own. Confirm the adopted edition and the amendments with the authority having jurisdiction before relying on any code figure here.
For an existing house asking "can I add this?", there is a different article
Most people arriving here are not building a house. They are adding one thing to a house that already exists, which is a different question with its own section of the Code.
NEC 220.83 exists for precisely this. “This section shall be permitted to be used to determine if the existing service or feeder is of sufficient capacity to serve additional loads.”
Not what service the house would need if you built it today — whether what is already there can carry one more thing. That is a narrower and much more answerable question.
The demand factors are slightly harsher. The first 8 kVA at 100 percent rather than 10 kVA, then the remainder at 40 percent.
So an existing-dwelling check on the same appliance list lands a little higher than the optional calculation for a new one.
That asymmetry is worth knowing about before you conclude that two electricians disagreed: they may simply have run different articles for different purposes.
And the heating rule changes shape. In NEC 220.83(B), where you are adding air conditioning or electric space heating, those go in at 100 percent — but “The larger connected load of air-conditioning or space-heating, but not both, shall be used.” The larger of the two, once. Again, not both.
Why this is the friendlier article for a homeowner. It produces a yes-or-no about a specific addition rather than a service size, and a yes on this article can end a conversation that was heading towards a panel replacement.
If you are being quoted a service upgrade to add a single appliance, asking whether the existing-dwelling calculation was run is a completely reasonable question and a professional will not be offended by it.
What it does not do. It says nothing about whether the panel has a physical space for the breaker, whether the busbar is rated for it, whether the panel is a make that still has listed breakers available, or whether the existing wiring is in a state worth adding to.
Those are four separate ways the answer can still be no.
The load can sometimes be managed instead of increased
Load management is the part of the subject that has changed most, and the part least likely to be raised by someone selling a service upgrade. It comes from the EV article, but the principle reaches further.
Illustrative, stated here rather than in a footnote. The unmanaged bars follow from the continuous-load rule; the managed bars simply show that the direction of the effect is downwards, not by how much in any particular house.The mechanism is NEC 625.42(A), 2023 edition. The magnitudes are ours and are illustrative.
The rule that makes charging expensive to calculate. NEC 625.42: “The EVSE shall have sufficient rating to supply the load served. Electric vehicle charging loads shall be considered to be continuous loads for the purposes of this article.”
Continuous means the circuit and its breaker are sized at 125 percent of the charging current, which is the same statement as the more familiar one that a continuous load may occupy no more than 80 percent of the circuit rating.
And the rule that can undo it. NEC 625.42(A): “Where an EMS in accordance with 750.30 provides load management of EVSE, the maximum equipment load on a service and feeder shall be the maximum load permitted by the EMS.”
Read that carefully, because it is the sentence that saves houses from unnecessary service upgrades: where a management system limits the load, the number that goes into the service calculation is the managed maximum, not the nameplate.
There is a second route in the same article. NEC 625.42(B): “EVSE with restricted access to an ampere adjusting means complying with 750.30(C) shall be permitted.” A charger commissioned at a lower current, with the adjustment not accessible to the occupant, is a smaller load than the same charger at its maximum.
The generalisation, carefully. The quoted allowance is about EV supply equipment specifically. But the idea underneath — that a controlled load is a smaller calculated load than an uncontrolled one — is the direction the whole subject is moving, and it is worth asking about for any large new load, not only a car.
What to actually ask. "Has a load calculation been run for this addition, and if it fails, does it still fail with the new load managed?"
NEC Article 702 (optional standby systems) and Article 705 (interconnected power production sources, including the busbar sizing allowance often called the "120 percent rule") are directly relevant to generator and battery work.
We did not retrieve verbatim text for either on the retrieved date, so no numeric rule from them is quoted anywhere on this site. Ask the electrician which article they are working to.
What a load calculation you can trust looks like on paper
You are entitled to see it. It is a page of arithmetic, not a trade secret, and every line on it should be traceable to something in your house or something in the Code.
It names the article it ran and the Code edition
Standard calculation or optional; new dwelling or existing; and which edition of the NEC your jurisdiction has adopted. Those three facts determine every number below them.
The floor area is a measured area with the exclusions applied
“The calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use.” If the area on the sheet matches the figure from the property listing, it probably includes a garage that should not be there.
The appliance lines are nameplates, not catalog figures
Read off the equipment, not looked up by model. Where an appliance is planned rather than installed, the sheet should say so and say which specification it assumed.
Heating and cooling appear once, as the larger of the two
“The largest of the following six selections (load in kVA) shall be included.” A sheet that adds a heat pump to an air conditioner is not following the article it cites, and the error always favors a larger service.
Continuous loads are identified as continuous
EV charging is named as continuous by the Code. If a charger appears on the sheet at its plain current with no continuous treatment, something has been missed — and this is the one direction where the error understates the load.
The conclusion is a number of amperes, compared with a stated existing service
Not "you need 200 A". A calculated demand in amperes, the existing service rating it is being compared against, and the margin between them.
If the answer is an upgrade, the sheet says which loads drove it
A good calculation makes the driver obvious, because that is what tells you whether managing one load would change the answer.
A verbal "your panel is too small", with no sheet
This is the thing to push back on, politely and once. There is no version of this work in which the arithmetic cannot be written down. Refusal to produce it is information.
When the answer really is a bigger service — and when it is not
Genuine reasons the service has to grow
The calculated demand exceeds the existing service and the excess is driven by loads that are long and overlapping rather than brief and occasional — resistance heat, a heat pump with strip backup, an induction hob and a car all in the same evening.
The existing service is below the 100 A that NEC 230.79(C) sets as the minimum for a one-family dwelling. A 60 A service is not merely tight; it is below the floor the Code sets for new work.
The service equipment itself is failing — a corroded or overheated meter enclosure, a service conductor problem, a panel with no listed breakers still made for it. This is an equipment argument, not a capacity argument, and it is a perfectly good reason on its own.
Several separate projects are planned in sequence. Doing the service once rather than three times is a real economic argument, and an honest contractor will frame it that way rather than as a capacity emergency.
Reasons that do not survive the arithmetic
The nameplate sum is large. It always is. It is not the calculated load and was never meant to be.
The panel is old. Age alone is not a capacity fact. A 1990s 200 A panel in good condition with spare positions has more usable capacity than a new 100 A one.
A single new appliance is being added and nobody ran the existing-dwelling calculation in NEC 220.83. That article exists to answer this exact question and it frequently answers yes.
The new load is a car charger and nobody mentioned load management. NEC 625.42(A) allows the managed maximum to be the number used, and a charger commissioned at a lower current is a smaller load.
The panel is out of spaces. That is a real problem and a different one — spaces and amperes are separate shortages with separate and usually much cheaper fixes.
What this tool cannot do
Specific blind spots, not a disclaimer. Each of these is a real way the number on this page can be right and still be the wrong basis for a decision.
It cannot see your conductors. Service and feeder conductor ampacity depends on material, insulation, installation method, ambient temperature and the temperature rating of the terminals at each end.
Conductor ampacity (NEC Article 310), including temperature correction and the terminal-temperature limits that decide the real answer, is not quoted numerically on this site.
It is a design question with more inputs than any web form has, and a wrong number there is a fire.
It cannot see the busbar or the panel label. A panel has a bus rating, a main breaker rating and a set of listing restrictions printed inside its door. Those can constrain what may be added irrespective of the calculated load.
It cannot see spaces. A calculation that comfortably passes tells you nothing about whether there is physically anywhere to land the new breaker. That is the panel space question and it fails independently of this one.
It does not run the standard calculation. Part III of Article 220 is a different and sometimes more favorable route, particularly where cooking appliances dominate, because of the range demand factors in NEC Table 220.55, Column C. An electrician may legitimately run either.
It knows nothing about your jurisdiction. Adoption and amendment of the National Electrical Code is local. A state or city may be on an older edition, may amend it, and may add rules of its own.
Confirm the adopted edition and the amendments with the authority having jurisdiction before relying on any code figure here. A local amendment can change a demand factor, a minimum, or whether the optional method is available at all.
And it is not a load calculation. Nothing on this site is a stamped load calculation, a design, or a permit document. A load calculation that an inspector accepts is produced by someone who has seen the building and signs for it.
HyreElectrical does not perform, supervise or warrant electrical work, does not open panels, and does not pull permits. HyreElectrical holds no dataset of bids, invoices, inspections or jobs. No figure on this site is our own measurement of the market.
The vocabulary, once
Six words that get used loosely in this conversation and precisely in the Code. Getting them straight is most of what it takes to follow a load calculation.
Nameplate rating
What the manufacturer states the equipment draws with everything in it operating. A worst-case figure about one appliance, and the correct basis for the circuit that feeds it. Not the basis for the service that feeds the house.
Calculated load
The result of running an article of the Code over those nameplates with demand factors applied. This is the number a service is sized against, and it is always smaller than the nameplate sum.
Demand factor
The percentage the Code applies to reflect that loads do not coincide. The optional method’s is “The general calculated load shall be not less than 100 percent of the first 10 kVA plus 40 percent of the remainder of the following loads”. Every demand factor is a codified statement about behavior.
Continuous load
A load expected to run for three hours or more. Sized at 125 percent — equivalently, held to 80 percent of the circuit. NEC 625.42 names EV charging as continuous explicitly.
Service
The conductors and equipment delivering power from the utility to the premises. Its rating is a capacity ceiling for the whole building. NEC 230.79(C) sets 100 A as the minimum for a one-family dwelling.
Volt-ampere (VA)
The unit load calculations are performed in. For resistive household loads it is numerically the same as the watt; the Code works in VA because it is sizing conductors against current, not billing you for energy.
Questions this calculator answers
What size electrical service do I need?
A licensed electrician calculates it from the adopted NEC edition and the actual nameplates in the house. This tool is a neighborhood check in the shape of the optional calculation in 220.82, so a “you need 200 A” pitch has something to be compared against.
Is 100 A enough for a heat pump and an EV charger?
Often not, once both are treated as large continuous loads. Run the numbers with your nameplates. Spare capacity on this page is illustrative.
Can I DIY a service upgrade?
No. Service work is licensed work. This page will not walk you through it.
Sources and methodology
Figures dated 23 August 2026. Last reviewed .
NFPA 70, National Electrical Code, Article 220 (NFPA, retrieved 2026-08-23. Cited as the model code. The optional-calculation shape used here is a simplification, not a reproduction of the article. Confirm the edition your jurisdiction adopted.)