Watts to Amps Calculator
- Last reviewed:
- | Reviewed to ensure accurate watts-to-amps conversions for DC, single-phase, and three-phase circuits.
Table of Contents
Use this watts to amps calculator to instantly convert electrical power into current for DC, single-phase and three-phase circuits. Enter your watts and voltage to see the result with the full formula and working shown.
Watts to Amps Calculator
Enter your values below to get your result with full working shown
Enter value in watts. For kilowatts, multiply by 1,000 first (e.g. 7.4 kW = 7,400 W)
For a simple learning example, leave this at 1. Motors and inductive loads typically use 0.7–0.95.
Result
—
A
Formula Used
Values Substituted
Step-by-Step Working
Plain English Explanation
Watts to Amps Formula
The formula used depends on the type of electrical supply.
DC circuits: I = P ÷ V
Single-phase AC circuits: I = P ÷ (V × PF)
Three-phase AC circuits: I = P ÷ (√3 × V × PF)
Where:
- I = Current in amps (A)
- P = Power in watts (W)
- V = Voltage in volts (V)
- PF = Power factor (0–1)
- √3 = Three-phase constant, approximately 1.732
Worked Example
UK single-phase example: A 7,400 W electric shower is connected to a 230 V single-phase supply with a power factor of 1.
I = P ÷ (V × PF) I = 7,400 ÷ (230 × 1) I = 32.17 A
US single-phase example: The same 7,400 W load on a 120 V supply:
I = 7,400 ÷ (120 × 1) I = 61.67 A
This shows why US circuits at 120 V carry significantly more current than UK circuits at 230 V for the same wattage.
Common Mistakes
- Entering kilowatts instead of watts. If your value is in kW, multiply by 1,000 first. For example, 7.4 kW = 7,400 W.
- Using the wrong voltage. UK single-phase is 230 V. UK three-phase is 400 V. US is 120 V or 240 V.
- Applying the single-phase formula to a three-phase load. The three-phase formula includes √3 (1.732) as a constant.
- Ignoring power factor on AC loads. Motors and inductive equipment typically operate at 0.7–0.95, not 1.
- Treating this result as a complete cable design. Current is only one factor. Always refer to BS 7671 for full design.
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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 seek advice from a competent qualified electrician or engineer.
Frequently Asked Questions
How do you convert watts to amps?
Divide the power in watts by the voltage in volts. For AC circuits, also divide by the power factor. Use the calculator above to see the full working.
What is the formula for watts to amps?
For DC: I = P ÷ V. For single-phase AC: I = P ÷ (V × PF). For three-phase AC: I = P ÷ (√3 × V × PF).
How many amps is 1,000 watts at 230 volts?
1,000 ÷ 230 = 4.35 amps (assuming a power factor of 1).
How many amps is 1,000 watts at 120 volts?
1,000 ÷ 120 = 8.33 amps (assuming a power factor of 1).
What is the difference between single-phase and three-phase amps?
Three-phase supplies divide the load across three conductors, which means each conductor carries less current than a single-phase supply of the same wattage. The three-phase formula uses √3 (1.732) as a constant to account for this.
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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