3-Phase Amps to kW Calculator
Three-phase real power uses √3 (≈1.732) for line-to-line voltage. This calculator handles 208 V, 400 V, 480 V and custom values.
Common conversions
| Input | Result |
|---|---|
| 30 A @ 208 V L-L (PF 0.9) | 9.73 kW |
| 65 A @ 400 V L-L (PF 0.88) | 39.63 kW |
| 90 A @ 480 V L-L (PF 0.86) | 64.35 kW |
| 100 A @ 600 V L-L (PF 0.9) | 93.53 kW |
| 40 A @ 277 V L-N (PF 0.87) | 28.92 kW |
| 75 A @ 120 V L-N (PF 0.9) | 24.30 kW |
| 150 A @ 240 V delta L-L (PF 0.8) | 49.88 kW |
| 20 A @ 380 V L-L (PF 0.95) | 12.51 kW |
The math behind it
- kW = √3 × V × A × PF / 1000
- kW = 1.7321 × 480 × 90 × 0.86 / 1000
- kW = 64,349 / 1000
Everything you need to know
Three-phase amps-to-kW conversions trip people up in a way single-phase math never does, because the same current reading can mean two different power levels depending on which voltage you pair it with. This page focuses on that specific problem: reading amps off a clamp meter or breaker schedule and turning them into real power for a three-phase system, correctly, whether the feeder is delta or wye, and whether your voltage number is line-to-line or line-to-neutral.
Line-to-line vs. line-to-neutral: same amps, different formula
A clamp meter on one conductor of a three-phase feeder reads the same current no matter which voltage you plan to use with it. What changes is the multiplier. If your voltage reading is line-to-line (the number on a transformer nameplate, like 208 V, 400 V, or 480 V), multiply by √3 (about 1.7321). If your voltage reading is line-to-neutral (the phase voltage measured from one hot leg to the grounded neutral), multiply by 3 instead. On a 480Y/277 V wye system these two paths agree: 90 A at 480 V L-L with PF 0.86 gives √3 × 480 × 90 × 0.86 / 1000 ≈ 64.35 kW, and the same load measured as 90 A at 277 V L-N gives 3 × 277 × 90 × 0.86 / 1000 ≈ 64.32 kW. The tiny gap is just rounding on 277 V (480 ÷ √3 = 277.13 V exactly). Pick one voltage reference and stick with its matching multiplier; never mix a line-to-line number with the ×3 formula or a line-to-neutral number with √3.
Delta systems don't give you a line-to-neutral option
Wye (star) services have a true neutral point, so both formulas are available and 480Y/277 V, 208Y/120 V, and 600Y/347 V are all standard label pairs you'll see on gear. Delta systems are three-wire with no center point, so there is no standard line-to-neutral voltage to plug into the ×3 formula, only the line-to-line voltage with √3. The exception that causes real damage is the high-leg (wild-leg) delta, a 240 V delta with one transformer winding center-tapped to create 120 V service for lighting. That center tap reads 120 V to two of the three legs but about 208 V to the third, the "wild leg." Using that 208 V reading in a standard L-N calculation, or worse, connecting 120 V loads to that leg, produces wrong power numbers and damaged equipment. If a panel schedule says "high leg" or "orange wire," treat the whole feeder with the line-to-line √3 formula only.
The current in the formula is per-line, and it assumes balance
Both formulas use the current from a single line conductor, not a sum of all three and not a per-phase average unless the load is genuinely balanced. On a balanced motor or heater bank, clamping any one of the three lines gives a representative reading. On lighting panels, VFDs feeding single-phase auxiliary loads, or a mix of 3-phase and 1-phase branch circuits sharing a feeder, the three line currents can differ by 10 to 30 percent. In that case, clamp all three lines individually, compute kW per phase using the appropriate single-phase relationship for the unbalanced portion, and sum the three results rather than multiplying one reading by three.
Common applications
Electricians clamp each line conductor at a panel, confirm the phases are within about 10% of each other, then use the line-to-line reading with √3 to report the connected kW for a load study or service upgrade.
Utility revenue meters sum V × A × PF across all three phases internally. Recomputing that total by hand from the CT ratio and line current is a standard way to sanity-check a suspiciously high or low bill.
Technicians dial resistive load banks to a target kW on a genset's line-to-line terminals. Knowing whether the unit is wye or delta determines whether individual phase legs can be tested against a neutral or only against each other.
Comparing per-line amps on a suspect motor circuit, rather than assuming balance, catches a failing winding or a loose lug before it trips the overloads or burns a conductor.
Common mistakes
480 V is a line-to-line number; running it through the ×3 (line-to-neutral) formula instead of √3 inflates the answer by about 73%.
Only wye systems have a true line-to-neutral voltage for the ×3 formula. Delta feeders, including 240 V and 480 V delta, only support the line-to-line √3 calculation.
The wild leg on a center-tapped 240 V delta reads about 208 V to neutral, not 120 V, and using it in standard single-phase or L-N math produces incorrect results and unsafe connections.
That approach assumes the other two legs carry identical current. On unbalanced panels, measure and calculate each phase separately, then sum, instead of tripling a single reading.
Frequently asked questions
Does a clamp meter read different amps for line-to-line vs. line-to-neutral math?+
No, the current on a conductor is the same number either way. Only the voltage you pair it with, and its matching multiplier (√3 for line-to-line, 3 for line-to-neutral), changes.
Can I use the line-to-neutral (×3) formula on a delta system?+
No, standard delta services have no usable line-to-neutral voltage. Use the line-to-line formula with √3 for delta feeders, including 240 V and 480 V delta.
What is the line-to-neutral voltage on a 480 V wye system?+
About 277 V. Divide the line-to-line voltage by √3: 480 ÷ 1.7321 ≈ 277.1 V, which is why 480Y/277 V is the standard label for that service.
How many amps does a 60 kW three-phase load draw at 480 V?+
About 82.0 A per line at PF 0.88, from A = (60,000) / (√3 × 480 × 0.88).
What happens if I use a line-to-line voltage with the ×3 formula by mistake?+
You overstate kW by roughly 73 percent, since 3 is √3 times larger than √3 itself. A 480 V, 90 A, PF 0.86 load that is really 64.35 kW would incorrectly compute to about 111.4 kW.
Is the wild leg of a 240 V high-leg delta usable for a standard L-N calculation?+
No, the wild leg reads about 208 V to neutral, not a standard phase voltage, and it should never be used for 120 V loads or plugged into the ×3 formula.
How do I convert three-phase amps to kW on an unbalanced load?+
Clamp each of the three lines separately, calculate the power contribution of each leg against its true voltage reference, and add the three results instead of scaling one reading by three.
How many amps is 100 kW at 400 V three-phase?+
About 160.4 A per line at PF 0.9, from A = (100,000) / (√3 × 400 × 0.9).
Do I divide the per-line amps by 3 before converting to kW?+
No, the √3 or 3 multiplier in the formula already accounts for all three lines. Dividing amps by 3 first and then applying the formula understates the result by a factor of 3.
Why does the same current deliver less power at 208 V than at 480 V?+
Because voltage is a direct multiplier in the formula. At identical current and PF, a 480 V line-to-line system delivers about 2.3 times the kW of a 208 V system (480 ÷ 208 ≈ 2.31).