Quick answer
Electrical power factor is the ratio of real power, measured in kilowatts (kW), to apparent power, measured in kilovolt-amperes (kVA), and shows how much of the current a load draws is doing useful work.
It runs from 0 to 1. A power factor of 1 means all the current does work. Motors and other inductive loads pull it lower, which raises current, losses and, for many businesses, the utility bill.
Quick facts
The key facts about Electrical Power Factor, with sources:
- Formula
- Power factor = real power (kW) ÷ apparent power (kVA) 1
- Range
- Between 0 and 1; higher is better 2
- Common penalty line
- Many utilities charge a fee below 0.95 1
- Main cause
- Inductive loads: motors, transformers, HID lighting 1
- Usual fix
- Capacitors, right-sized motors, less idling 1
- On home bills?
- No; it appears on commercial and industrial bills 2
Key takeaways
- Power factor compares the power that does work (kW) to the power the wires must carry (kVA).
- Motors and transformers need magnetizing current that does no useful work; that is reactive power, in kVAR.
- Low power factor means more current for the same work, so more heat and voltage drop.
- Businesses often pay a penalty below about 0.95; homes are billed on kWh and usually never see it.
- Capacitors cancel reactive power and are the standard fix.
What power factor means
Every AC load draws current. Some of that current does real work, like turning a fan or heating a coil. That is real power, measured in kilowatts. Some loads also need current to build a magnetic field. That current flows back and forth but does no work. It is reactive power, measured in kilovars (kVAR).
The wires and transformers must carry both. The total they carry is apparent power, measured in kilovolt-amperes (kVA). Power factor is the share of that total that does real work. The DOE defines it as the ratio of real power to apparent power 1.
The DOE uses a picture of a horse pulling a rail car from the side of the track. The pull along the track is real power. The sideways pull is wasted effort, or reactive power. The horse’s total effort is apparent power 1.
PF = kW ÷ kVA, where kVA² = kW² + kVAR²
kW- Real power that does work
kVAR- Reactive power for magnetic fields
kVA- Apparent power the wires carry
PF- Between 0 and 1
The squared relationship is the “power triangle” DOE uses in its fact sheet.
Source: [1]
Why inductive loads lower it
Inductive loads, such as motors, transformers and high-intensity discharge lighting, need current to make a magnetic field. The DOE says these loads are the cause of low power factor and a major share of industrial use 1.
In those loads the current wave lags behind the voltage wave. The Kansas Corporation Commission fact sheet explains that when voltage and current are in sync, all supplied power is real; when they are out of step, part of the supplied power is reactive 2.
Induction motors in refrigeration, HVAC and pumps are the most common cause, especially when they run lightly loaded 2.
Capacitors do the opposite of inductors. The DOE explains that a capacitor stores and releases kVAR that oppose the inductor’s, so the two trade energy locally instead of pulling it from the utility 1.
Kinds of power factor and loads
| Kind | What it means | Typical source |
|---|---|---|
| Unity (1.0) | Current and voltage in step; all power does work | Resistive heaters, incandescent lamps |
| Lagging | Current lags voltage | Motors, transformers 2 |
| Leading | Current leads voltage | Capacitors, some lightly loaded electronics |
| Displacement PF | Caused by the phase shift between waves | Motors |
| Distortion effects | Caused by non-smooth current from electronics | Power supplies; addressed by PF-corrected designs |
Example: DOE’s capacitor correction worked through
The power factor numbers here come straight from the DOE fact sheet “Reducing Power Factor Cost” 1.
| Step | Math | Result |
|---|---|---|
| Load | Real power | 100 kW |
| Before correction | 100 kW ÷ 142 kVA | PF 0.70 |
| Add capacitors | Reactive power offset by capacitors | Apparent power falls to 105 kVA |
| After correction | 100 kW ÷ 105 kVA | PF 0.95 |
| Effect on current | From 142 to 105 kVA | About 26% less current |
Less current for the same work means cooler wires and less voltage drop. Our voltage drop calculator shows how current and wire length interact.
Where you meet power factor
On a commercial or industrial utility bill, power factor or kVAR may be listed next to kWh and kW demand. The Kansas fact sheet notes it does not appear on residential bills 2.
On equipment, you see PF on motor nameplates, LED drivers and UPS spec sheets. ENERGY STAR requires voltage-independent and double-conversion UPS units to have a power factor of at least 0.9 3.
Solar inverters can be set to hold a power factor or to supply reactive power under IEEE 1547 4, which DOE describes as part of how inverters help balance the grid 5.
At home, you meet it indirectly. A generator or UPS rated in both watts and VA reflects power factor: the watt rating is the real power it can deliver.
Benefits of a high power factor, and the limits
Benefits of correcting it
Limits
- Does not lower kWh used by the load itself.
- Capacitors must be sized and placed by engineers or suppliers 1.
- Overcorrection can cause leading power factor problems.
- Little to gain for a typical home on a kWh-only rate.
What power factor does not tell you
- Power factor does not measure the efficiency of the device itself; a motor can have high PF and still waste energy as heat.
- It does not show on a typical home bill 2.
- Penalty thresholds vary by utility; check your tariff.
- A single PF number hides changes over the day as loads start and stop.
What drives the cost of correction
No prices here. These factors decide whether correction pays off for a business.
- Size of the penalty. Set by the utility tariff.
- kVAR needed. More reactive power means more capacitor capacity 1.
- Where capacitors go. At each motor or at the service.
- Motor upgrades. Replacing worn motors with efficient ones as they fail 1.
- Load profile. Lightly loaded motors drag PF lower 1.
- Lifespan. Capacitors age; ask the supplier about expected service life and warranty.
How a business corrects power factor
Power factor correction is engineering and electrician work. DOE says capacitor suppliers and engineering firms can help size and locate capacitors 1.
- Read 12 months of bills for kW, kVA or kVAR and any PF charge.
- Find the big inductive loads and how loaded they run.
- Cut idling and right-size motors where possible 1.
- Size and place capacitors, often with an engineer.
- Install under permit, then confirm the new PF on the next bills.
- Real power (kW)Does the work; billed as kWh over time
- Reactive power (kVAR)Builds magnetic fields in motors and transformers
- Apparent power (kVA)The total the wires and transformers must carry
Source: [1]
Keeping it corrected
- Review PF on bills each month after correction.
- Have capacitor banks checked on the maker’s schedule.
- Revisit sizing when motors are added or removed.
- Avoid running equipment above its rated voltage 1.
Warning signs
A rising PF charge on a commercial bill, warm feeders, or motors running hot can point to low power factor. Capacitor banks that bulge, leak or smell burnt need an electrician right away.
At home, flickering lights or warm cords are not power factor issues; they are signs to call an electrician. Our safety check lists the common ones.
Capacitors store charge
Power factor capacitors can hold a dangerous charge after power is turned off. Never open a capacitor bank or motor starter. Leave testing and service to a qualified electrician.
Rules and standards that touch power factor
| Authority | Rule | What it says |
|---|---|---|
| Utility tariffs | Commercial and industrial rate schedules | Many charge a fee below 0.95; thresholds vary 1 |
| ENERGY STAR | UPS specification (current) | VI and VFI UPS units must have PF ≥ 0.9 3 |
| IEEE | IEEE 1547-2018 | Inverters may hold a set power factor or supply reactive power 4 |
| NFPA 70 (NEC) | Edition your state adopts | Covers capacitor installation safety, not PF targets |
Power factor vs related terms
| Term | Unit | What it measures |
|---|---|---|
| Real power (watts) | kW | Work done |
| Apparent power | kVA | Volts × amps carried |
| Reactive power | kVAR | Magnetizing current, no work |
| Energy use (kWh) | kWh | Energy over time; what homes pay for |
| Voltage drop | Volts or % | Loss along wires; worse with more current |
Myths
- Myth A power factor saver will cut my home bill.
- Reality Homes are billed on kWh, and power factor is not on residential bills 2.
- Myth Low PF means the device uses more kWh.
- Reality It means more current for the same kW; the main cost is losses and utility penalties 1.
- Myth Power factor and efficiency are the same.
- Reality They measure different things.
Why it varies by place
Power factor charges are set in each utility’s tariff, approved by the state utility commission, so thresholds and fees differ by state and utility. Common thresholds sit between 0.90 and 0.95 2.
Does it matter to you?
For a home, rarely: your meter bills kWh, and a box sold as a home power factor saver will not change that number. For a shop, farm or plant with motors, look for a PF charge on the bill. If it is there, correction can pay for itself.
Either way, the first step is reading the bill. For building loads, start with the load calculation page.
Quick test
No kVAR or power factor line on your bill? You are not paying for it directly.
Questions about Electrical Power Factor
What is power factor in simple terms?
Power factor is the share of the current a load draws that does useful work. It is real power in kilowatts divided by apparent power in kilovolt-amperes. A value of 1 means all current does work. Motors and transformers need extra current for their magnetic fields, which pulls the number below 1.
What is a good power factor?
Closer to 1 is better. DOE says many utilities charge an extra fee when a customer’s power factor falls below 0.95, and the Kansas Corporation Commission notes some set the line at 0.90.
Many businesses aim for at least 0.95 to avoid penalties. Homes are not billed for it, so it rarely matters for a household.
What causes low power factor?
Inductive loads cause it. DOE lists transformers, electric motors and high-intensity discharge lighting. These need current to build magnetic fields, and that current does no useful work. Lightly loaded or idling motors make it worse, which is why right-sizing motors is one of the fixes.
How do you correct power factor?
The standard fix is adding capacitors, which supply the reactive power that motors need locally instead of drawing it from the utility. DOE also suggests cutting idle motor time, avoiding running equipment above rated voltage, and replacing worn motors with efficient ones. Capacitor sizing and placement should be done by an engineer or supplier.
Does power factor affect my home electric bill?
Not directly. Residential customers are billed for kilowatt-hours, and the Kansas Corporation Commission fact sheet notes power factor does not appear on residential bills. Devices sold as home power factor savers do not lower the kWh your meter records. Focus on using less energy instead.
What is the difference between kW and kVA?
kW is real power, the part that does work. kVA is apparent power, the total the wires carry, including reactive power. Power factor links them: kW equals kVA times power factor. That is why generators and UPS units list both, and why the watt rating is what you size loads against.
What is reactive power?
Reactive power, measured in kVAR, is the power that motors and transformers use to build and collapse their magnetic fields each cycle. It flows back and forth without doing work, but it still loads wires and transformers. Capacitors can supply it locally, which raises power factor.
Do solar inverters affect power factor?
They can. Under IEEE 1547-2018, inverters can hold a set power factor or supply and absorb reactive power to help steady grid voltage, if the utility asks for it. DOE notes modern inverters can provide this reactive support. For a home owner, this is set by the installer and utility, not adjusted by you.
Can power factor correction save energy?
It lowers current, which cuts heat losses in wires and transformers and frees capacity, and it avoids utility penalties. It does not reduce the energy the motor itself needs to do its work. The biggest savings show up as smaller demand and penalty charges on commercial bills.
Sources
- U.S. DOE Motor Challenge, Fact Sheet: Reducing Power Factor Cost, retrieved .
- Kansas Corporation Commission / K-State Engineering Extension, PEP Fact Sheet: Power Factor (2019), retrieved .
- ENERGY STAR, Uninterruptible Power Supplies, retrieved .
- Solar Builder, Smart PV inverter overview: IEEE 1547-2018 and UL 1741 explained, retrieved .
- U.S. DOE, Solar Integration: Inverters and Grid Services Basics, 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: Formula and example taken from DOE’s power factor fact sheet; billing context from the Kansas Corporation Commission fact sheet; equipment rules from ENERGY STAR and IEEE 1547 summaries; checked 2026-10-10.
Suggest a correction. We fix errors and say what changed.