Amps to Watts Calculator - DC, Single-Phase and Three-Phase

Agarapu Ramesh — Editor and content reviewer
Editorially reviewed Reviewed by Agarapu Ramesh, science educator (chemistry). LinkedIn
Last reviewed: May 2026 | Standard electrical engineering formulas

Watts are not hidden inside amps. You need voltage, and for AC loads you need power factor. DC watts = volts x amps. Single-phase watts = volts x amps x PF. Three-phase watts = 1.732 x line volts x amps x PF.

Formula at a glance

  • DC: W = V x A
  • single-phase: W = V x A x PF
  • three-phase: W = 1.732 x V x A x PF

Field note: A breaker rating is a limit, not a load measurement. A 20 A circuit is not automatically using 2,400 W.

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Calculator Tool

Convert current (A) to power (W)

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How to Convert Amps to Watts

To convert current (Amps) to power (Watts), you use the formula: Watts = Amps × Volts.

Example Calculation

Scenario: A 120V appliance draws 15 Amps.

Calculation: P = 15A × 120V = 1800 Watts.

For AC circuits, especially those with motors, you must also multiply by the Power Factor (PF).

Quick Reference

Amps @ 120V @ 240V
5A 600W 1200W
10A 1200W 2400W
15A 1800W 3600W
20A 2400W 4800W
30A 3600W 7200W

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Watts to Amps Amps to kW Ohm's Law

How to use the Amps to Watts Calculator

Use this as a fast electrical check, then compare the result with the nameplate, measured voltage and power factor. The formula is clean. Real panels, motors and UPS loads usually have one extra wrinkle.

Worked example

Example: 15 A at 120 V with PF 0.9 is 1,620 W. If the same 15 A is a heater at PF 1, it is 1,800 W.

Practical checks before you trust the number

  • Power factor changes watts, not the amp reading on your clamp meter.
  • Motors, compressors and fluorescent ballasts need realistic PF values.
  • Use VA for UPS sizing and W for energy or heat calculations.

Common mistake

A breaker rating is a limit, not a load measurement. A 20 A circuit is not automatically using 2,400 W.

Sources and references

Related calculators

Frequently Asked Questions

Watts = volts × amps for DC. For single-phase AC, Watts = V × A × PF. For three-phase, Watts = √3 × V × A × PF. The formula you pick depends on whether it's DC, single-phase, or three-phase. Example: 230 V, 5 A, PF = 0.9 single-phase: W = 230 × 5 × 0.9 = 1035 W. Always include PF for any motor, fluorescent ballast, or compressor — leaving it out gives a wrong real-power figure.

DC power: P = V × I. Easy and clean — no PF, no √3. Example: a 12 V solar panel pushing 8 A delivers 96 W. For battery sizing or inverter input calculations this is the formula you use. The same battery delivering 30 A means 360 W of load is connected. Keep this rule front of mind for solar and EV charging work where DC is everywhere now.

Single-phase AC: W = V × A × PF. The PF is critical because most household loads are not purely resistive anymore. Example: a refrigerator draws 3 A on 230 V at PF 0.7 → real power = 230 × 3 × 0.7 = 483 W. The apparent power (VA) is higher at 690 VA. Inverter and UPS sizing should use VA, but billing is on W. Knowing both keeps your sizing and cost calculations honest.

Three-phase: W = √3 × V_line × A_line × PF. Example: 415 V, 12 A, PF 0.85 → W = 1.732 × 415 × 12 × 0.85 = 7,328 W or about 7.3 kW. Use line-to-line voltage and line current — that's the convention. If you accidentally plug phase voltage (240 V) instead of line voltage (415 V) into the formula, your answer is off by a √3 factor and your motor sizing falls apart.

Power factor scales the apparent power down to real power. W = V × A × PF. Without PF you'd get the apparent power (VA), which is what the cables and breaker carry, but not what the meter records. Example: 230 V, 10 A: VA = 2300, but at PF 0.7 real W = 1610. The 690 VAR difference is reactive power, mostly carried as magnetizing current. Improve PF with capacitors and you reduce both your bill and your cable losses.

On 120 V at PF 1 (heater, lamp): W = 10 × 120 = 1200 W. At PF 0.8 (small motor): W = 10 × 120 × 0.8 = 960 W. The current looks the same on the meter, but the energy delivered is different. This is why two devices with identical amp readings can have very different power and energy consumption. Junior techs often mix this up when comparing appliances.

Yes. Read amps from the device nameplate or a clamp meter, multiply by voltage and PF, and you get the real power draw. Example: 230 V, 6 A clamp reading on a fan, PF 0.95 → W = 230 × 6 × 0.95 = 1311 W. Add up these per-device values for total connected load on a feeder. For approximate home audits this works fine, but for billing-grade accuracy use a proper power meter.