Free tool
Amps to kW Calculator
Amps times volts times power factor, divided by a thousand — and times 1.732 on three-phase. What a plain converter never asks is whether the amps are a load or a breaker rating, and those two answer different questions.
kW = amps × volts × power factor ÷ 1,000
kW = amps × volts × power factor ÷ 1,000 on single-phase, and × 1.732 as well on three-phase using the line-to-line voltage. 30 A at 240 V is 7.2 kW; 100 A at 480 V three-phase and 0.9 power factor is 74.8 kW.
From a breaker rating, that figure is a ceiling: a continuous load may use only 80 percent of it, so a 40 A, 240 V circuit carries 7.68 kW continuously, not 9.6. From a motor's current, the result is its input; its shaft output is lower by the efficiency.
The current
The supply voltage.
1.00 for a resistive heater; about 0.85 for a loaded motor. A nameplate figure beats any preset.
The answer
Real power
7.20 kW
30.0 A × 240 V × 1.00 PF ÷ 1,000
Apparent power: 7.20 kVA, equal to the kW at a power factor of 1.
What this does not tell you
Energy or cost. kW is a rate. Energy is kW × hours of running, and what a bill charges for is kWh.
Whether a circuit is adequate. That depends on conductor ampacity, terminal ratings and the equipment's installation instructions, which state its required circuit and govern.
Informational use only, please verify before you rely on it
This reproduces standard conversion arithmetic from current to real power in kW for DC, single-phase and three-phase systems, with power factor applied, the 80 percent continuous-load figure for a breaker rating (NEC 210.19(A)(1) and 210.20(A)), and, for motors, shaft output from efficiency. It is a preparation aid, not a determination and not a design. It does not size conductors or overcurrent protection, does not replace the NEC 430.248 and 430.250 full-load current tables for motor circuits, and does not calculate a dwelling service or feeder load. Confirm against the equipment nameplate and installation instructions and with the authority having jurisdiction.
This tool is provided for general informational and educational purposes only. Its output is an illustrative estimate generated from the values you enter and from general assumptions that will not match every deal, market, lender, or homeowner. It is not tax, legal, accounting, financial, or professional advice, and it is not a quote, an offer, a credit decision, or a guarantee of pricing, approval, timing, savings, or eligibility.
You are solely responsible for independently confirming all information presented here including any figures, rates, fees, margins, timelines, tax treatment, and federal, state, local, or utility incentives, with the applicable lender, authority having jurisdiction, and your own qualified tax, legal, and financial advisors before acting on it, relying on it, or presenting it to a homeowner or any third party. Incentive programs, lender terms, and permitting requirements change frequently and vary by jurisdiction.
Seamless Home is not a tax advisor, law firm, lender, or licensed installing contractor, and makes no representation or warranty as to the accuracy, completeness, or currency of the information produced by this tool. To the fullest extent permitted by law, Seamless Home accepts no liability for any decision made or action taken in reliance on it.
Two different questions behind “amps to kW”
The first is “how much power is this using?” — a clamp-meter reading or a nameplate current, converted straight across. The second is “how much can this circuit carry?” — a breaker rating, where the answer is a ceiling and the usable figure for anything that runs for hours is 80 percent of it. The amps to watts calculator takes that second question further, to the NEC 210.23(A) limits on a single plug-in appliance.
On solar and storage work, the conversion runs both ways: a panel's busbar and main breaker set what can be backfed, which the solar backfeed capacity calculator checks, and a battery's kW rating has to cover the circuits it backs up, which is what the critical load panel planner works through. When the rating starts in kW, the kW to amps calculator goes the other way; the difference between kW and kVA is covered in what power factor is.
Frequently Asked Questions
How do you convert amps to kW?+
Multiply amps by volts, and by the power factor on AC, then divide by 1,000. On three-phase, multiply by the square root of three as well, using the line-to-line voltage. 30 A at 240 V and a power factor of 1 is 7.2 kW. 100 A at 480 V three-phase and a power factor of 0.9 is 74.8 kW. On DC there is no power factor: 100 A from a 48 V battery bank is 4.8 kW.
How many kW can a 40 amp circuit handle?+
At 240 V, 40 A is 9.6 kW at the full rating — but a continuous load, one that runs three hours or more, may draw only 80 percent of the rating, 32 A, which is 7.68 kW. That is because NEC 210.19(A)(1) and 210.20(A) size the circuit at 125 percent of the continuous load. EV charging and water heating are continuous; the equipment's installation instructions state the circuit it needs.
How many kW is 200 amps?+
At 240 V single-phase and a power factor of 1, 200 A is 48 kW; the continuous figure at 80 percent is 38.4 kW. On a 208 V three-phase service it is about 72 kW, and at 480 V three-phase about 166 kW. A 200 A service rating is a ceiling on what the service can supply, not a measure of what a house uses — actual demand is far lower most of the time.
Why do amps give a larger kW than the motor's nameplate?+
Because the current a motor draws is its electrical input, and its nameplate kW or horsepower is its mechanical output at the shaft. The difference is the motor's losses. A three-phase motor drawing 12.3 A at 460 V with a power factor of 0.85 takes about 8.33 kW; at 90 percent efficiency it delivers about 7.5 kW, or 10 hp, at the shaft.
What is the difference between kW and kVA?+
kW is real power, the part doing work; kVA is apparent power, volts times amps, which is what the wiring and transformers carry. kW = kVA × power factor. 30 A at 240 V is 7.2 kVA; at a power factor of 0.85 that is 6.12 kW. On a resistive load such as a heater they are the same.
Which voltage do I use on three-phase?+
The line-to-line voltage: 208, 240 or 480. On a 208Y/120 or 480Y/277 system the second number is line-to-neutral, and using it in the three-phase formula understates the power by about 1.73 times. The tool flags 120 V and 277 V entries on three-phase and shows the corrected figure.
Is this a determination?+
No. It reproduces the standard conversion arithmetic as a preparation aid. It does not size conductors or overcurrent protection, does not replace the NEC Article 430 tables for motor circuits, and does not calculate a service or feeder load. Confirm against the equipment nameplate and installation instructions and with the authority having jurisdiction.
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Seamless Home runs the design, engineering and permit layer for the partners it works with, which is where currents and ratings are carried through to circuits on a plan set rather than converted on a job site. Coverage is confirmed per service area rather than promised as blanket availability.
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