What the result means
On a balanced three-phase system, power is 1.732 times line voltage times line current. Multiply by power factor to get real power (kW), the part that does work. Without power factor you get apparent power (kVA), which is what conductors and transformers must carry.
Use the solve modes to estimate current for a known kW load, or to back-calculate voltage from a clamp reading and a known load.
How it's calculated
- P (kW) = 1.732 × V × I × PF ÷ 1,000
- S (kVA) = 1.732 × V × I ÷ 1,000
- I = P × 1,000 ÷ (1.732 × V × PF)
- kVAR = √(kVA² − kW²)
V is line-to-line voltage. Assumes a balanced load.
Worked example
A 480 V three-phase load drawing 50 A at 0.9 power factor.
- kW = 1.732 × 480 × 50 × 0.9 ÷ 1,000 = 37.41 kW
- kVA = 1.732 × 480 × 50 ÷ 1,000 = 41.57 kVA
The load does 37.41 kW of work while the supply carries 41.57 kVA.
Reference table
The values below are computed from the same calculator functions used above. They let you compare common sizes and operating points without replacing the interactive calculation or its assumptions.
| kVA | Amps | kW at 0.90 PF |
|---|---|---|
| 15 | 18.04 | 13.50 |
| 30 | 36.09 | 27.00 |
| 45 | 54.13 | 40.50 |
| 75 | 90.21 | 67.50 |
| 100 | 120.28 | 90.00 |
| 150 | 180.43 | 135.00 |
| 225 | 270.64 | 202.50 |
Reference values are examples based on the stated assumptions. Verify manufacturer data, conductor ampacity and local requirements before using a result.
Sources and assumptions
V is line-to-line voltage. Assumes a balanced load. Calculator formulas are published with their units so a technician can check a result instead of treating it as a black box.
Last reviewed . Spot an error? Email support@tiermenu.com.
FAQ
What voltage do I use, line-to-line or line-to-neutral?
Line-to-line (for example 208, 240 or 480 V). The 1.732 factor already accounts for the phase relationship.
What power factor should I assume?
Use the nameplate or a power meter. Resistive heat is 1.0. Motors vary with load, often lower at light load.
What if my phases are unbalanced?
Measure each phase and use the average current as an estimate, or calculate each phase separately.
Why is kVA higher than kW?
With power factor below 1, some current circulates without doing work. Equipment still has to carry it.
Using a reference result in the field
A calculator is most useful when the inputs match the job being checked. Where a field asks for a length, confirm whether it is one-way or total; where it asks for current, confirm whether the load is continuous or intermittent. The unit label beside the result is part of the result; do not carry a number into another calculation without checking its units.
Reference rows are provided for comparison, not as universal design limits. They use the values and conditions stated with each table. A different conductor material, temperature, power factor or load type can change a field result. Where the page calls out a code check, equipment rating or manufacturer table, that check remains part of the job.
Use the interactive inputs for the exact conditions at hand, then review the displayed formula and assumptions. If a value looks unexpected, change one input at a time and compare it with a known point in the reference table. Keep the measured readings and job-specific notes with the work record so another technician can understand how the result was obtained.
TierMenu provides these free calculators without an email gate. The results stay in this browser unless you choose to copy a shareable URL or print the page. A shared URL includes the calculator inputs in its query string; do not put personal or sensitive information in calculator fields.