Quick answer
Amperage is the amount of electric current flowing through a circuit, counted in amperes (amps, A): the quantity of electric charge that passes a point each second.
The ampere is an SI base unit. Breakers, fuses, wires and home services are all rated in amps, because current is what heats a wire. More amps than a part is rated for means overheating.
Quick facts
The key facts about Amperage, with sources:
Key takeaways
- Amperage is how much current flows. Voltage pushes it; resistance limits it.
- You can work it out: amps = watts ÷ volts. A 1,500 W heater on 120 V draws 12.5 A.
- Breakers, wires and services are rated in amps because current is what heats them.
- The body is very sensitive: OSHA lists 50 to 150 milliamps as possibly fatal. A 15 A circuit carries 15,000 milliamps.
- Electric current and amperage name the same thing. This page covers both.
Amperage in plain terms
If voltage is the water pressure in a hose, amperage is how much water flows through it each second. It tells you how much electricity is moving, not how hard it is being pushed.
NIST describes the ampere as the measure of how much charge passes a point each second. It ties the ampere to the coulomb, the unit of charge: one coulomb equals one ampere for one second 1. The ampere is one of the seven SI base units 2.
Small currents are written in milliamps (mA). One amp equals 1,000 milliamps. Shock limits and GFCI trip points use milliamps, because the body reacts to tiny currents.
Electric current and amperage: the same thing
People search for “electric current” and “amperage” as if they were two ideas. They are one. Electric current is the flow of charge. Amperage is the size of that flow, read in amps. Saying “the current is 10 amps” and “the amperage is 10” mean the same.
Current comes in two forms. Direct current flows one way, as from a battery. Alternating current reverses direction, 60 times a second on the US grid 5. Both are measured in amps.
Current vs. capacity
A circuit’s amp rating is its limit, not what it is using. A 20 A circuit with one lamp on might carry half an amp. The rating tells you how much it can carry before the breaker should trip.
How amperage is set in a circuit
The circuit does not “push” amps. The load pulls them. Voltage stays about the same, and each device you turn on lowers the total resistance, so more current flows. That is Ohm’s law: amps equal volts divided by ohms. NIST defines one ohm as one volt per amp 1.
Every amp flowing through a wire makes some heat. Double the current and the heat in the wire rises about four times. That is why wire size and breaker size are matched to a current limit, not a voltage.
Virginia Tech Extension notes you can find an appliance’s watts by multiplying its amps by its voltage. Turn that around and amps equal watts divided by volts 3.
Amps = Watts ÷ Volts · Amps = Volts ÷ Ohms
Watts- From the appliance nameplate
Volts- 120 V or 240 V in a US home
Ohms- The resistance of the load
Kinds of amp ratings you will see
| Rating | What it means | Where |
|---|---|---|
| Load current | What a device actually draws while running | Nameplate, clamp meter reading |
| Breaker rating | The current at which the breaker is built to trip | The number on the breaker handle |
| Branch-circuit rating | Set by the breaker size; 2023 NEC lists 10, 15, 20, 30, 40 and 50 A for multi-outlet circuits 6 | Panel directory |
| Service rating | The most the whole home can draw at once | Main breaker, often 100 or 200 A |
| Milliamp leakage | Tiny current escaping to ground | GFCIs trip near 5 mA 4 |
Example: will these appliances share one 20-amp circuit?
Wattages are the upper ends of the ranges listed by Virginia Tech Extension 3. Amps = watts ÷ 120 V.
| Appliance | Watts (upper) | Amps at 120 V |
|---|---|---|
| Portable heater | 1,500 | 12.5 A |
| Hair dryer | 1,875 | About 15.6 A |
| Microwave | 1,100 | About 9.2 A |
| Toaster | 1,400 | About 11.7 A |
| Heater + hair dryer together | 3,375 | About 28.1 A, over a 20 A circuit |
Any two of the big heat-makers together go past 20 amps. That is an overload, and the breaker should trip. Spread loads across circuits, or see the appliance circuit lookup.
Where amperage shows up in your home
Look at the panel. Each breaker handle shows a number: 15, 20, 30, 40, 50. That is its amp rating. The main breaker at the top shows the service size. Our guide to finding your service size walks through it.
Appliance nameplates list amps, or watts you can turn into amps. EV chargers list both the charging amps and the breaker size they need. Quotes list wire gauges, which match amp limits.
Why amps are the number to watch
Amps are what you add up to see if a circuit or a panel is overloaded. Watts tell you energy use, and volts tell you the supply, but amps tell you whether the wires are safe.
Amps also explain safety devices. A breaker counts current through it. A GFCI compares current going out with current coming back and trips if they differ by more than 5 milliamps 4.
What amperage does not tell you
Amps alone do not give energy use or cost. A 10-amp load at 240 V uses twice the power of a 10-amp load at 120 V. For your bill, convert to watts and then to kilowatt-hours.
Nameplate amps are a maximum. Motors pull a burst of current when they start, then settle. Fridges cycle on and off. Real draw can differ from the label.
How amps affect the cost of electrical work
We do not quote prices. These amp-driven factors move them. See panel upgrade cost drivers.
- Higher-amp circuits need thicker wire. Copper costs more per foot as size goes up.
- Breaker size. Larger and specialty breakers cost more.
- Service size. If total amps exceed the service, a service upgrade may follow.
- Load management. Some EV jobs avoid an upgrade by limiting charging amps.
- Lifespan. Wires run close to their amp limit for long hours run warmer. Sizing with headroom helps them last.
How an electrician checks amperage
- Reads nameplates and the panel directory to list what is on each circuit.
- Measures running current with a clamp meter, without opening wires.
- Adds up loads in a load calculation for the service.
- Compares totals with breaker, wire and service ratings.
- Recommends moving loads, adding circuits or upgrading, and pulls a permit for new work.
Keeping current within limits
Risks and warning signs of too much current
Too much current heats wires, plugs and outlets. Warning signs are warm wall plates, a burning smell, scorch marks, buzzing and breakers that trip often. Shut off the load and call an electrician.
Current through the body is the other risk. OSHA lists effects from a faint tingle at 1 mA to cardiac arrest at 10,000 mA 4. Wet hands lower skin resistance and let more current through.
Small current, big harm
The current that can stop a heart is a small fraction of what a household circuit can deliver. Never touch exposed wires. If a breaker will not stay on, leave it off and call an electrician.
Code rules built around amps
The 2023 NEC 210.18 rates a branch circuit by its breaker or fuse, not the wire. It lists 10, 15, 20, 30, 40 and 50 amps for circuits that are not individual circuits, and the 10-amp size is new in 2023 6.
The 2023 NEC 625.42 treats EV charging as a continuous load 7. The circuit is sized at 125 percent of the charging current. The current edition is the 2026 NEC, free to read at NFPA 10; what applies is what your jurisdiction adopted.
Amperage compared with related terms
| Term | What it is | Unit |
|---|---|---|
| Amperage (current) | Rate of charge flow | Amp (A) |
| Voltage | The push behind the flow | Volt (V) |
| Wattage | Rate of work; volts × amps | Watt (W) |
| Overload | Current above a circuit’s rating for too long | Amps over rating |
| Breaker rating | The current that should trip the breaker | Amp (A) |
Myths about amps
- Myth A bigger breaker fixes nuisance trips.
- Reality The breaker protects the wire. A bigger one on the same wire lets it overheat. The CPSC warns that oversizing fuses is a serious fire hazard 9.
- Myth It is the volts that kill, not the amps.
- Reality OSHA ranks effects by current 4. Voltage matters because it drives that current.
- Myth A 200 A service means 200 A per outlet.
- Reality Each circuit is limited by its own breaker, often 15 or 20 A.
What changes by state
The physics is the same everywhere. What changes is which NEC edition sets the amp rules your inspector checks, such as whether 10-amp branch circuits are allowed under the 2023 edition 6, and who may do the work. Check your local edition and license rules.
When amperage matters to you
Amperage matters when breakers trip, when you add a big appliance or charger, and when you wonder if your panel is big enough. Add up the amps on the circuit or run the load calculator for the whole home.
If the numbers come close to a rating, ask a licensed electrician before adding more.
Tools for checking current
- Panel space checkRoom for new breakers
- Wire size calculatorMatch wire to amps
Questions about Amperage
What is amperage?
Amperage is the amount of electric current flowing in a circuit, measured in amps. NIST describes it as how much charge passes a point each second. One amp equals one coulomb per second. It is what breakers, fuses and wires are rated for, because current is what heats them.
Is electric current the same as amperage?
Yes. Electric current is the flow of charge, and amperage is the size of that flow in amps. The terms are used the same way. Current can be direct, flowing one way, or alternating, reversing 60 times a second on the US grid. Both are measured in amps.
How do I calculate amps from watts?
Divide watts by volts. A 1,500-watt heater on a 120-volt outlet draws 12.5 amps. The same rule works backward: Virginia Tech Extension notes that amps times volts gives watts. Use the nameplate watts, which is the maximum draw, for a safe estimate.
How many amps can a 15 amp circuit handle?
A 15-amp circuit is built to carry up to 15 amps, and its breaker should trip above that. For continuous loads such as EV charging, the 2023 NEC sizes the circuit at 125 percent of the load, which keeps that load at 80 percent of the rating, or 12 amps on a 15-amp circuit.
How many amps does it take to kill a person?
Far less than one amp. OSHA lists 50 to 150 milliamps as possibly fatal and 1,000 to 4,300 milliamps as the range where the heart stops pumping. A milliamp is a thousandth of an amp. A household circuit can deliver many times these amounts.
What is the difference between amps and volts?
Volts are the push and amps are the flow. Voltage is the pressure between two points, and amperage is how much charge moves because of it. A 240-volt circuit can deliver the same power as a 120-volt circuit with half the amps.
What does a 20 amp breaker mean?
It means the breaker is rated to trip when current goes past 20 amps for long enough. The 2023 NEC rates a branch circuit by its breaker size. It is matched to the wire, often 12 AWG copper, so the wire never carries more current than it can handle.
What is a milliamp?
A milliamp is one thousandth of an amp. It is used for tiny currents such as shock thresholds and GFCI trip points. OSHA notes that GFCIs shut off power when outgoing and returning current differ by more than 5 milliamps.
How many amps does a house use?
It varies minute by minute. A home with a 200-amp service can draw up to 200 amps at once, but usually draws far less. An electrician works out the expected peak with a load calculation, which adds lighting, appliances, heating and cooling using code demand factors.
Sources
- NIST, SI Units: Electric Current, retrieved .
- NIST, SI Units (base and derived units), retrieved .
- Virginia Cooperative Extension, How to Estimate Appliance Energy Use (pub. 2901-9014), retrieved .
- OSHA 3075, Controlling Electrical Hazards, retrieved .
- U.S. Department of Energy, The War of the Currents: AC vs. DC Power, retrieved .
- NEC 2023 210.18 Branch Circuit Rating (code change summary), ElectricalLicenseRenewal.com, retrieved .
- NEC 2023 625.42 Rating (EVSE), ElectricalLicenseRenewal.com, retrieved .
- U.S. CPSC, safety information on circuit breakers and fuses (1983, rev. 2011), retrieved .
- U.S. CPSC, CPSC and NESF Urge Consumers to Plug Into Electrical Safety (2000), retrieved .
- NFPA 70, National Electrical Code, 2026 edition (free access), retrieved .
Expert review
Written by the HyreElectrical Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Unit definitions from NIST; shock thresholds quoted from OSHA 3075; appliance watts from Virginia Cooperative Extension; code rules from 2023 NEC change summaries. Amp math is illustrative.
Suggest a correction. We fix errors and say what changed.