Three Phase Power Calculator
Enter the line voltage, current and power factor and get kW, kVA and kVAR — or enter the power and get the line current — for three-phase or single-phase loads.
1 for heaters; from the nameplate for motors.
The result updates as you type.
Power
21.2 kW · 24.94 kVA
13.14 kVAR reactive · 30 A at 480 V, PF 0.85
| Apparent power | 24.942 kVA = √3 × V × I ÷ 1000 |
| Real power | 21.2 kW = kVA × PF |
| Reactive power | 13.139 kVAR |
| Phase voltage in a Y (line ÷ √3) | 277.1 V |
What this page cannot tell you
Unbalanced loads, harmonics, or what size wire, breaker or transformer the load needs — those come from the electrical code and equipment data. Motor nameplate current already includes efficiency and power factor at full load; partial loads differ.
How to calculate three-phase power
- Choose three-phase or single-phase. Three-phase assumes a balanced load.
- Enter the voltage. Line-to-line voltage, such as 208, 480 or 600 V.
- Enter the power factor. 1 for resistive loads like heaters; motor power factor from its nameplate.
- Enter current or power. Get power from amps, or amps from kW.
10 situations where a three-phase power calculator helps
Motor current from kW
Turn a load's kW into line amps at your voltage.
Clamp-meter readings to kW
Measured amps and voltage give the real power.
Generator sizing conversations
Generators are rated in kVA and kW; see both.
Heater banks
Resistive loads at PF 1 — kW straight from amps.
208 V vs 240 V single-phase
Compare current for the same load.
Power factor correction
kVAR shows the reactive part that capacitors offset.
Comparing 208 and 480 V service
Higher voltage, lower current for the same power.
Horsepower output
Add the motor efficiency to estimate shaft hp.
Exam and coursework checks
Verify hand calculations of √3 V I PF.
Transformer loading
kVA of the load compared with a transformer's rating.
The formulas and where they come from
In a balanced three-phase system each of the three phases carries the same power, so total power is three times one phase. Kuphaldt's open textbook 'Lessons In Electric Circuits' (Vol. II, ch. 10) shows that in a Y connection the line voltage is the phase voltage times the square root of 3 while line and phase currents are equal, and in a delta the line current is √3 × the phase current. Either way, apparent power S = √3 × V(line) × I(line). For single phase, S = V × I.
Real power P = S × power factor, and reactive power Q = S × sin(arccos PF); power factor is the ratio of true power to apparent power (ch. 11). Horsepower output = kW × efficiency ÷ 0.7457.
Limits: the formulas assume a balanced, sinusoidal load. Unbalanced loads need each phase worked separately, and harmonics change the picture. Sizing wire, breakers and transformers follows the electrical code and equipment data, not just this arithmetic. Everything runs in your browser.
Sources
- Kuphaldt — Lessons In Electric Circuits Vol. II, ch. 10: Three-phase Y and Delta Configurations — √3 relations between line and phase
- Kuphaldt — Lessons In Electric Circuits Vol. II, ch. 11: Calculating Power Factor — True power = apparent power × power factor
Frequently asked questions
What is the three-phase power formula?
P (W) = √3 × V(line) × I(line) × power factor. At 480 V, 30 A and PF 0.85: 21.2 kW.
How do I calculate amps from kW for three-phase?
I = kW × 1000 ÷ (√3 × V × PF). 20 kW at 480 V and PF 0.85 is 28.3 A.
What's the difference between kW and kVA?
kVA is apparent power (V × I); kW is the real power that does work, kVA × power factor.
What power factor should I use?
1 for resistive loads. For motors, use the nameplate or measured value; it changes with load.
Why √3?
In a balanced three-phase system line voltage and phase voltage (or line and phase current) differ by √3, so total power works out to √3 × V(line) × I(line).
Does this work for unbalanced loads?
No — each phase has to be calculated separately and added.
Related tools
DC Voltage Drop Calculator
Enter the voltage, current, run length and copper wire gauge and get the voltage drop, the percent lost, the voltage at the load and the thinnest AWG that stays within your limit.
NBS Handbook 100, Copper Wire Tables
Electricity Cost Calculator
Enter an appliance's watts and hours of use and get its electricity cost per day, month and year at your state's average rate.
EIA Electric Power Monthly Table 5.6.A (residential price by state)
Propane Usage Calculator
Enter your propane appliances' Btu ratings and daily run time and get the gallons you burn per day and month, how long your tank will last and the cost.
EIA heat content: propane 91,452 Btu per gallon
Heating Oil Usage Calculator
Enter your burner's nozzle size and run time, or your heat load, and get the gallons of heating oil used per day and month, how long your tank will last and the cost.
EIA heat content: heating oil 138,500 Btu per gallon
What Soil Type Is My Property?
Enter an address and get the soil series, texture, drainage, pH and depth to water table for that exact spot.
USDA NRCS Soil Data Access (SSURGO)
OSHA Soil Classification
Answer the questions OSHA's criteria ask and get the soil type — A, B, C or stable rock — with the clause that decides it.
OSHA 29 CFR 1926 Subpart P, Appendix A