Wattage to Amperage Calculator

Enter a power value and circuit voltage to find the current in amps using I = P ÷ V, with adjustments for AC power factor and three-phase √3 scaling.

Quick Facts

DC circuits
I = P ÷ V
Current equals power divided by voltage; power factor does not apply to DC.
AC single-phase
I = P ÷ (V × PF)
Power factor (PF) accounts for the phase difference between voltage and current in inductive or capacitive loads.
AC three-phase
I = P ÷ (√3 × V × PF)
√3 ≈ 1.732 accounts for the 120° phase offset between the three line conductors.
Typical power factors
0.95-1.0 resistive, 0.7-0.9 motors
Use PF = 1 only for purely resistive loads such as heaters or incandescent bulbs.

Your Results

Calculated
Current
-
I = P ÷ V, adjusted for AC and power factor
Apparent Power
-
S = P ÷ PF; equals real power when PF = 1
Power Factor Used
-
1.00 for DC circuits
Recommended Wire/Breaker Rating
-
125% of current, per NEC continuous-load guidance

Ready

Enter power, voltage, circuit type, and power factor, then press Calculate.

Formula and Method for Converting Watts to Amps

Electrical power (P, in watts) equals voltage (V, in volts) times current (I, in amps). Rearranging that relationship gives the current: I = P ÷ V for direct current (DC). Alternating current (AC) circuits add a power factor (PF) that accounts for the phase difference between voltage and current, and three-phase circuits add a √3 (≈ 1.732) factor because the three line conductors are offset by 120°. This calculator applies the correct version of the formula based on the circuit type you select.

Choosing the right formula

DC circuits use I = P ÷ V because voltage and current are always in phase. AC single-phase circuits use I = P ÷ (V × PF), since only the portion of power in phase with the voltage does real work. AC three-phase circuits use I = P ÷ (√3 × V × PF), where V is the line-to-line voltage and I is the current in each line conductor. Purely resistive loads — baseboard heaters, incandescent bulbs, toasters — have PF ≈ 1; motors, transformers, and switching power supplies typically run PF between 0.7 and 0.95.

Real power vs. apparent power

Watts (W) measure real power, the power that actually does work. Volt-amps (VA) measure apparent power, the total power the source must supply, including the portion that oscillates between source and load without doing work. Apparent power is always at least as large as real power: S = P ÷ PF. When PF = 1, watts and volt-amps are numerically equal; as PF drops, the current — and therefore the required wire and breaker size — climbs even though the wattage stays the same.

Sizing wire and breakers safely

Once you have the calculated current, do not size a breaker or conductor to exactly that number. The U.S. National Electrical Code (NEC 210.19/210.20) requires branch circuits serving continuous loads (running 3 hours or more) to be rated at 125% of the continuous current. This calculator shows that 125% figure as a starting reference — always confirm final wire gauge and breaker sizing against your local electrical code and, for anything beyond a simple plug-in appliance, a licensed electrician.

Frequently Asked Questions

What is the formula to convert watts to amps?
For DC circuits, amps = watts ÷ volts (I = P ÷ V). For AC single-phase circuits, amps = watts ÷ (volts × power factor). For AC three-phase circuits, amps = watts ÷ (√3 × volts × power factor), where √3 ≈ 1.732 and voltage is the line-to-line voltage.
Why do I need a power factor for AC but not DC?
In a DC circuit, voltage and current are always perfectly in phase, so all delivered power does useful work. In an AC circuit, inductive or capacitive loads such as motors and transformers shift current out of phase with voltage, so only a fraction of the apparent power does real work. A purely resistive AC load has a power factor near 1, matching the DC case.
What power factor should I use if I do not know the exact value?
For purely resistive loads such as incandescent bulbs, heaters, and toasters, use a power factor of 1. For general household appliances and small motors, 0.85 to 0.95 is a common estimate. For industrial motors and HVAC equipment, check the equipment nameplate — power factor often ranges from 0.7 to 0.9 and is usually printed on the label.
Why is my three-phase current lower than watts divided by volts?
Three-phase power delivers P = √3 × V × I × PF, not P = V × I. Dividing by the extra √3 (about 1.732) factor, on top of the power factor, is why the per-line current for a given wattage is lower than a simple watts-divided-by-volts calculation would suggest.

Related calculators