Amps to Watts Calculator
- Last reviewed:
- | Reviewed to ensure accurate amps-to-watts conversions for DC, single-phase, and three-phase circuits.
Table of Contents
Use this amps to watts calculator to convert electrical current into power for DC, single-phase and three-phase circuits. Enter your amps and voltage to see the result with the full formula and working shown — including the kW equivalent of your answer.
Amps to Watts Calculator
Enter your values below to get your result with full working shown
Enter the current in amperes (A)
Leave at 1 for a simple learning example. Motors and inductive loads typically use 0.7–0.95.
Result
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W
Formula Used
Values Substituted
Step-by-Step Working
Also Expressed As
Plain English Explanation
Amps to Watts Formula
The formula used to convert amps to watts depends on the type of electrical supply.
DC circuits: P = I × V
Single-phase AC circuits: P = I × V × PF
Three-phase AC circuits: P = √3 × I × V × PF
Where:
- P = Power in watts (W)
- I = Current in amps (A)
- V = Voltage in volts (V)
- PF = Power factor (0–1)
- √3 = Three-phase constant, approximately 1.732
To convert the result to kilowatts, divide by 1,000.
Worked Example
UK single-phase example: A circuit carries 32 A at 230 V single-phase with a power factor of 1.
P = I × V × PF P = 32 × 230 × 1 = 7,360 W In kilowatts: 7,360 ÷ 1,000 = 7.36 kW
UK three-phase example: A three-phase motor draws 17 A per phase at 400 V with a power factor of 0.85.
P = √3 × I × V × PF P = 1.732 × 17 × 400 × 0.85 = 10,002 W In kilowatts: 10,002 ÷ 1,000 = 10.0 kW
US single-phase example: A circuit carries 32 A at 120 V single-phase with a power factor of 1.
P = 32 × 120 × 1 = 3,840 W In kilowatts: 3,840 ÷ 1,000 = 3.84 kW
Common Mistakes
- Confusing amps to watts with watts to amps. If you already know the watts and want to find amps, use the Watts to Amps Calculator instead.
- Using the wrong voltage. UK single-phase is 230 V. UK three-phase is 400 V line-to-line. US is 120 V or 240 V single-phase.
- Ignoring power factor on AC loads. Resistive loads such as heaters use PF = 1. Motors and inductive loads typically operate at 0.7–0.95, which reduces the real power produced.
- Applying the single-phase formula to a three-phase load. Three-phase circuits use √3 (1.732) as a constant and produce significantly more power for the same current.
- Forgetting to convert watts to kilowatts. Divide your watt result by 1,000 to express it in kW. The calculator does this automatically in the result panel.
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Disclaimer: This calculator is provided for learning and revision purposes only. Results must not be used as the basis for electrical design, inspection, testing, verification or any on-site decision. Always refer to the current edition of BS 7671 and seek advice from a competent qualified electrician or engineer.
Frequently Asked Questions
How do you convert amps to watts?
Multiply the current in amps by the voltage in volts. For AC circuits, also multiply by the power factor. Use the calculator above to see the full step-by-step working.
What is the formula for amps to watts?
For DC: P = I × V. For single-phase AC: P = I × V × PF. For three-phase AC: P = √3 × I × V × PF.
How many watts is 1 amp at 230 volts?
P = 1 × 230 × 1 = 230 W (assuming a power factor of 1).
How many watts is 1 amp at 120 volts?
P = 1 × 120 × 1 = 120 W (assuming a power factor of 1).
How many watts is 13 amps at 230 volts?
P = 13 × 230 × 1 = 2,990 W, or approximately 3 kW. This is the maximum load for a standard 13 A plug socket in the UK.
What is the difference between watts and kilowatts?
A kilowatt (kW) is equal to 1,000 watts. To convert watts to kilowatts, divide by 1,000. To convert kilowatts to watts, multiply by 1,000.
Why does three-phase use √3 in the formula?
In a three-phase system, the line voltage and phase voltage are related by a factor of √3 (approximately 1.732). This constant is included in the power formula to correctly calculate total power across all three phases.
Is this calculator suitable for electrical design?
No. This calculator is for learning and revision only. For electrical design, always refer to BS 7671 and consult a qualified electrician or engineer.
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