Watts to Amps Calculator

By Hassan Nawaz, B.Sc. Electrical Engineering. Updated November 6, 2026.

Enter watts and voltage, choose the circuit type, and get the current in amps. Add a power factor for motors and other inductive AC loads.

1.0 for heaters and incandescent; about 0.8 to 0.9 for motors.
12.50 A
Current
63%
Load on a 20 A circuit

Watts to amps formulas

DC: I = P ÷ V
AC single phase: I = P ÷ (V × PF)
AC three phase: I = P ÷ (1.732 × V × PF)

P is real power in watts, V is voltage, and PF is power factor. A 1,500 W space heater on 120 V draws 1,500 ÷ 120 = 12.5 A.

Common appliances at 120 V

ApplianceWattsAmps
Space heater1,50012.5
Microwave1,1009.2
Hair dryer1,80015.0
Window AC (8,000 BTU)7005.8
Laptop charger650.5
The 80% rule. A continuous load should not exceed 80% of the breaker rating: 12 A on a 15 A circuit, 16 A on a 20 A circuit. Need the reverse? Use the amps to watts calculator.

How many amps is 1500 watts?

12.5 amps on 120 V, so a 1,500 W heater draws 12.5 A. That is 83% of a 15 A circuit and 63% of a 20 A circuit, so a 1,500 W heater should be the only large load on a 15 A circuit.

Frequently asked questions

How many amps is 1,500 watts?

12.5 amps at 120 V, or 6.25 amps at 240 V.

How many watts can a 15 amp circuit handle?

1,800 W at 120 V in total, or 1,440 W for a continuous load under the 80% rule.

What power factor should I use?

Use 1.0 for resistive loads such as heaters. Motors and compressors typically run at 0.8 to 0.9; check the nameplate when you can.

Sources

Reference charts

Embed this calculator on your website

Free for blogs, suppliers, clubs and schools. Paste this code to show the Watts to Amps Calculator on your page. It updates itself, and the credit line to WhatSizeWire under it must stay in place.

More electrical calculators

Voltage Drop Calculator

Volts lost, percent drop and load voltage for DC or AC runs.

Wire Size Calculator

Smallest AWG for your amps and distance, AC or DC.

Conduit Fill Calculator

Fill percent and max wires for EMT and PVC.

Amps to Watts Calculator

Convert current to power, with kVA.

Ground Wire Size Calculator

Ground wire size by breaker rating, per NEC 250.122.

VA to Watts Calculator

VA to watts and back, using power factor.

Last updated November 6, 2026. Results are estimates for planning. See how we build and check our tools in our editorial policy. Found an error? Tell us.