Power Factor Calculator
This power factor calculator finds your power factor from real power and apparent power, and shows the phase angle and reactive power. Enter kW and kVA, and the power factor calculator reveals how efficiently your system uses the power it draws.
Results
The Power Factor Calculator is part of our AC & Three Phase collection. Browse more ac & three phase to size, convert, and check your work alongside this tool.
What the power factor calculator does
The power factor calculator measures how well your system converts supplied power into useful work. Power factor is the ratio of real power to apparent power, and this power factor calculator returns that ratio along with the phase angle and reactive power. A low reading from the power factor calculator often means wasted capacity and utility penalties.
Power factor formula
The power factor calculator uses the ratio of real to apparent power:
The phase angle is the inverse cosine of the power factor, and the reactive power comes from the power triangle:
These three quantities form a right triangle, which is the geometry behind every power factor calculation.
Power factor calculator example
A site drawing 5 kW of real power while the supply delivers 6.25 kVA:
The power factor calculation gives a phase angle near 36.9 degrees and about 3.75 kVAR of reactive power. A power factor of 0.8 means 20 percent of the supplied capacity does no useful work, so power factor correction of around 3.75 kVAR would bring it close to unity.
How to use the power factor calculator
Enter the real power in kilowatts and the apparent power in kilovolt-amperes. The power factor calculator returns the power factor as a number from 0 to 1, the phase angle in degrees, and the reactive power in kVAR. A result near 1 is excellent; below 0.9 the power factor calculator is telling you correction may pay off.
Reading the power factor result
A power factor above 0.95 is excellent, 0.9 to 0.95 is good, and below 0.9 usually warrants power factor correction. The reactive power figure from the power factor calculator is roughly the size of capacitor bank needed to correct to unity. Improving the power factor cuts current, lowers losses, and removes demand penalties.
When to use a power factor calculator
- Assessing how efficiently a facility uses power
- Sizing a capacitor bank for power factor correction
- Avoiding utility penalties flagged by a low power factor
- Analysing motor loads that drag the power factor down
Common power factor calculation mistakes
- Confusing kW and kVA. The power factor calculator needs real power in kW and apparent power in kVA in the right fields.
- Over-correcting. Too much capacitance pushes into a leading power factor with its own penalties.
- Ignoring harmonics. Electronic loads lower the true power factor in ways capacitors alone cannot fix.
Tips for accurate power factor results
- Measure at a representative load, since power factor changes with load.
- Size correction from the reactive power the power factor calculator reports.
- Check your tariff to see how much a poor power factor costs.
The power triangle behind the power factor calculator
To read the power factor calculator well, picture the power triangle. Real power in kW is the base, reactive power in kVAR is the vertical side, and apparent power in kVA is the hypotenuse. The angle between the base and hypotenuse is the phase angle, and its cosine is the power factor. When reactive power grows, the triangle stretches taller, the angle opens, and the power factor falls. This geometry is why the power factor calculator can find all three from just real and apparent power.
Why utilities care about power factor
A utility builds its network for apparent power, not real power, so a customer with a poor power factor forces it to supply more current than the useful work needs. The power factor calculator exposes this gap, which is why commercial tariffs charge for low power factor. Power factor correction with capacitors pays back on several fronts: lower current, less loss in cables and transformers, freed capacity, and no penalty. Running the power factor calculator is the first step in deciding whether that correction is worth it.
Reference Table
| Power factor | Rating | Action |
|---|---|---|
| 0.95-1.00 | Excellent | No correction |
| 0.90-0.95 | Good | Optional |
| Below 0.90 | Poor | Correct it |
Power Factor Calculator FAQ
What is a good power factor?
Anything above 0.95 is excellent. Between 0.9 and 0.95 is good, and below 0.9 the power factor calculator is signalling that power factor correction would cut current and penalties.
How do I improve power factor?
The usual method is a capacitor bank sized from the reactive power figure the power factor calculator gives. Capacitors supply reactive power locally, raising the power factor toward unity.
Why is low power factor a problem?
A low power factor means more current for the same useful power, which wastes capacity, heats cables, and triggers utility charges. The power factor calculator quantifies how far from unity you are.