How Many Watts Per Amp?

One ampere equals a different number of watts depending on the circuit voltage. At 12 volts, 1 amp = 12 watts. At 120 volts, 1 amp = 120 watts. At 240 volts, 1 amp = 240 watts. The formula is: Watts = Amps × Volts.

To calculate for any specific voltage, use the Amps to Watts Calculator.

Watts Per Amp at Common Voltages

Circuit VoltageWatts per 1 AmpCommon Use
5 V5 WUSB charging
9 V9 WSmall DC devices
12 V12 WAutomotive, RV, solar
24 V24 WLED drivers, some DC systems
48 V48 WTelecom, solar battery
120 V120 WUS household outlets
208 V208 WCommercial 3-phase (Y)
220 V220 WInternational appliances
230 V230 WUK, EU mains
240 V240 WUS split-phase, AU/NZ
277 V277 WCommercial lighting
480 V480 WIndustrial 3-phase

The Formula: Why Watts Depend on Voltage

Watts per amp isn't a fixed number — it scales directly with voltage because of Watt's Law: P = I × V.

Why Isn't There a Fixed "Watts Per Amp" Answer?

Unlike a fixed conversion (like 1 mile = 1.609 km), watts per amp requires voltage as an input. Without voltage, the conversion is incomplete.

DC vs AC Watts Per Amp

For DC circuits, watts per amp = voltage (simple multiplication, no power factor).

For AC circuits with inductive loads, real watts per amp = voltage × power factor.

Example: On a 120V AC circuit with a motor at PF 0.85: Watts per amp = 120 × 0.85 = 102 real watts per amp (not 120W).

Frequently Asked Questions

How many watts is 1 amp?

1 amp equals 120 watts at 120 volts, or 240 watts at 240 volts. In a 12V DC system, 1 amp equals 12 watts.

Is there a fixed number of watts per amp?

No, watts per amp is not fixed. It changes depending on the voltage of the circuit.

What is 1 amp at 120 volts?

1 amp at 120 volts is exactly 120 watts for a resistive load.

How does power factor change watts per amp?

In AC circuits with inductive loads, you must multiply the apparent power (V × A) by the power factor (PF) to get real watts per amp. This means the real watts will be lower than the apparent watts if the PF is less than 1.0.

Apply This Knowledge

Start with the main conversion tool

Use these calculator pages to apply the concept to real current, voltage, watts, and power-factor problems.Amps to Watts Calculator

Methodology, Review Notes, and Sources

How this calculator works

The calculator applies Watt's law for DC and resistive loads, then adds power factor for AC loads and the 1.732 multiplier for balanced three-phase line-to-line calculations.

  • DC and resistive loads: W = A x V
  • Single-phase AC: W = A x V x PF
  • Three-phase AC: W = 1.732 x A x V x PF

Editorial review

Last reviewed: June 26, 2026. Ampstowatt.com is built around the amps to watts conversion — our core specialty. Content is maintained by the Ampstowatt editorial team and checked for formula consistency, unit labels, calculator behavior, and safety wording.

The page is an educational planning reference, not a licensed electrical design or inspection service.

Reference sources

FAQ

Frequently Asked Questions

Fast answers for the amps to watts formula, common conversions, and safe planning limits.

W How do I convert amps to watts?

Multiply amps by volts to get watts. For example, 10 amps at 120 volts equals 1,200 watts (10 × 120 = 1,200). For AC circuits with motors or compressors, also multiply by the power factor from the equipment nameplate.

AC What is the formula for amps to watts?

There are three formulas depending on the circuit type. DC: Watts = Amps × Volts. AC single-phase: Watts = Amps × Volts × Power Factor. AC three-phase (line-to-line): Watts = 1.732 × Amps × Volts × Power Factor. For three-phase line-to-neutral: Watts = 3 × Amps × Volts × Power Factor.

1A How many watts are in 1 amp?

1 amp equals a different number of watts depending on the voltage. At 12V, 1 amp = 12 watts. At 120V, 1 amp = 120 watts. At 240V, 1 amp = 240 watts. This assumes power factor of 1.00. For AC motor loads with lower power factor, the real watts will be lower.

V Do I need voltage to convert amps to watts?

Yes — you cannot convert amps to watts without knowing the voltage. Amps measure current flow, and watts measure power. The relationship is Watts = Amps × Volts. Without voltage, there is no way to determine how much power the current represents. A 10-amp load could be 120 watts (at 12V) or 2,400 watts (at 240V).

PF Why does AC amps to watts need power factor?

Power factor (PF) measures how efficiently a device uses current. Resistive loads like heaters use all the current for real work (PF = 1.0). Motors and compressors draw extra current due to inductance, so their power factor is lower (0.70–0.95). Without accounting for PF, you would overestimate watts by 10–40% for these loads.

VS What is the difference between amps and watts?

Amps (amperes) measure the flow rate of electric current — how much charge passes a point per second. Watts measure electric power — the rate at which electrical energy is used or converted to heat, light, or motion. You need both amps and volts to calculate watts: Watts = Amps × Volts.

3P How do I convert three-phase amps to watts?

For three-phase with line-to-line voltage: Watts = √3 × Amps × Volts × Power Factor (√3 ≈ 1.732). For line-to-neutral voltage: Watts = 3 × Amps × Volts × PF. Example: 10A at 480V with PF 0.90 using line-to-line voltage = 1.732 × 10 × 480 × 0.90 = 7,478 watts.

Wh Is watts the same as watt-hours?

No. Watts (W) measure instantaneous power — how fast energy is being used right now. Watt-hours (Wh) measure total energy consumed over time. A 100-watt light bulb running for 3 hours uses 300 watt-hours (0.3 kWh). Your electricity bill charges per kilowatt-hour, not per watt.

APP Can I use this calculator for appliances?

Yes. Enter the amperage from the appliance nameplate, the outlet voltage (120V or 240V in the US), and power factor if listed. For resistive appliances (heaters, toasters, hair dryers), use PF = 1.0. For motor-driven appliances (refrigerators, AC units, washing machines), use the nameplate PF or estimate 0.85.

SA Can I use this calculator for breaker or wire sizing?

You can use the result for load planning, but not for final breaker or wire sizing. The NEC requires that continuous loads (3+ hours) stay at or below 80% of the breaker rating. Final sizing must account for wire gauge, ambient temperature, conduit fill, voltage drop, and local code. Always consult a licensed electrician for safety-critical work.