Amps to Watts Calculator

Convert amps to watts at any voltage and power factor.

This conversion is for load estimation only. Circuit and equipment sizing must follow the NEC and be verified by a licensed electrician.

How this calculator works

watts = volts × amps × power factor

For three-phase, multiply by 1.732 as well. Power factor is the gap between real power in watts and apparent power in volt-amps — generators and UPS units are rated in VA for exactly this reason.

Switch the site to metric — the control is in the footer — and your inputs, your results and the tables below follow. The formula, the constants, the guidance text and the sources stay in US units on purpose: that is how the standards they come from are written, and restating them would detach each figure from the document you are meant to be able to check it against.

Where these numbers come from

NFPA 70 (National Electrical Code) 2023, Article 220 — how volt-amperes and watts are counted in a load calculation
NIST Special Publication 811 2008 — the √3 factor relating line and phase quantities in a balanced three-phase system

The edition matters as much as the number. Jurisdictions adopt code revisions on their own schedule, so verify which one applies where you are building.

Worked example

With current 15 , voltage 120 , power factor 1 , this calculator returns 1800 .

Watts drawn by common circuits and appliances

Open any row to load it into the calculator above — the link carries the numbers with it, so it can go straight to a supplier or a crew.

Job	Size	Real power
Bedroom receptacle circuit	15 × 120 × 1	1,800
Kitchen small-appliance circuit	20 × 120 × 1	2,400
Electric range	40 × 240 × 1	9,600
Well pump motor Motors run below unity power factor	10 × 240 × 0.85	2,040
Shop dust collector	15 × 240 × 0.8	2,880

Resistive loads — heaters, ovens, incandescent lamps — sit at a power factor of 1. Motors and electronics do not.

Frequently asked questions

How many watts is 15 amps?

At 120 V with a resistive load, 1,800 watts. At 240 V the same 15 amps delivers 3,600 watts, which is why heavy appliances run on the higher voltage.

What is power factor?

The ratio of real power to apparent power. Resistive loads like heaters and incandescent lamps have a power factor of 1. Motors and transformers run 0.8 to 0.9 because current lags voltage.

What is the difference between watts and VA?

Watts is the power actually doing work; VA is the product of voltage and current regardless of phase. They are equal only at unity power factor. Generators and UPS units are rated in VA because that is what the wiring carries.

How do I convert for three-phase?

Multiply by 1.732, the square root of three. Three-phase watts equals volts times amps times power factor times 1.732, using line-to-line voltage.

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