How many amps does my appliance draw? Convert between amps, watts, volts, and ohms. Get wire size and breaker recommendations per NEC code.
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Last updated March 2026 by our expert review team
| Appliance | Watts | Volts | Amps |
|---|---|---|---|
| Microwave | 1,000-1,500 | 120V | 8.3-12.5A |
| Hair Dryer | 1,500 | 120V | 12.5A |
| Space Heater | 1,500 | 120V | 12.5A |
| Window AC | 500-1,500 | 120V | 4.2-12.5A |
| Electric Dryer | 5,000 | 240V | 20.8A |
| Electric Range | 8,000-12,000 | 240V | 33.3-50.0A |
| EV Charger (L2) | 7,200 | 240V | 30.0A |
| Hot Tub | 6,000 | 240V | 25.0A |
Based on single-phase resistive loads (power factor 1.0). Motor loads draw more amps due to lower power factor.
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How we verify our calculatorsNEC requires circuits to be sized at 125% of continuous loads. A 12-amp appliance needs a 15-amp circuit minimum.
120V circuits use 14 AWG wire (15A) or 12 AWG (20A). 240V circuits use 10 AWG (30A) or 8 AWG (40A).
After determining wire gauge, use our conduit fill calculator to size conduit for the run.
Three-phase power delivers 1.73x more power than single-phase at the same voltage. Common in commercial and industrial settings.
Never exceed 80% of a breaker's rated capacity for continuous loads. A 20-amp breaker should carry no more than 16 amps continuously.
Use our recessed lighting calculator to determine lighting circuit loads before sizing wire.
Select a calculation mode (Watts & Volts, Volts & Ohms, or Watts & Ohms) and enter the two known values.
Choose single-phase (residential) or three-phase (commercial). For three-phase, set the power factor.
Get the amperage, all derived values, and NEC-compliant wire size and breaker recommendations.
Ohm's Law and Power Formulas
Amps = Watts / Volts (single phase)
Amps = Watts / (Volts x sqrt(3) x PF) (three phase)
Amps = Volts / Ohms
Amps = sqrt(Watts / Ohms)
Wire sizing: Amps x 1.25 (NEC 125% continuous load rule)
How many amps does 1500 watts draw at 120 volts?
12.5 amps. Use a 20-amp circuit with 12 AWG wire.
What is the formula for amps?
Amps = Watts / Volts for resistive loads. For AC with power factor: Amps = Watts / (Volts x PF).
What wire size for 30 amps?
10 AWG copper wire for runs up to 50 feet. Use 8 AWG for longer runs to reduce voltage drop.
How do I know what size breaker I need?
Calculate the amperage, multiply by 1.25 for continuous loads, and select the next standard breaker size (15, 20, 30, 40, 50, 60).
What is the difference between watts and amps?
Watts measure power consumed. Amps measure current flow. Watts = Amps x Volts.
Single phase vs three phase?
Single phase uses one live wire (residential). Three phase uses three live wires delivering 1.73x more power (commercial/industrial).
What is power factor?
The ratio of real power to apparent power in AC circuits. Resistive loads (heaters) have PF of 1.0. Motors have PF of 0.8 to 0.95.
How many amps can 12 AWG wire handle?
20 amps maximum per NEC. At 80% continuous rating, that is 16 amps of continuous load.
A standard kitchen microwave drawing 10 amps. Fits on a dedicated 15-amp circuit with room to spare under the 80% rule.
A 240-volt dryer circuit. The 125% NEC rule bumps the requirement from 20.8A to 26A, so a 30-amp breaker with 10 AWG wire is the correct choice.
A dedicated 240-volt EV charging circuit. At 30 amps continuous, NEC requires 37.5A capacity, so a 40-amp breaker with 8 AWG wire is needed.
A three-phase motor with 0.85 power factor. The lower power factor means the motor draws more current than a purely resistive load of the same wattage.
Using watts and amps interchangeably
Watts measure power consumed while amps measure current flow. They are related by voltage: Watts = Amps x Volts. A 1,500-watt heater draws 12.5 amps at 120V but only 6.25 amps at 240V.
Forgetting the 125% rule for continuous loads
NEC requires breakers to be sized at 125% of the continuous load. A 16-amp load needs a 20-amp breaker, not a 15-amp. Undersized breakers trip repeatedly under normal use.
Using 120V calculations for 240V appliances
Doubling the voltage halves the amperage. A 4,800-watt dryer draws 40 amps at 120V but only 20 amps at 240V. Always verify the appliance voltage on the nameplate.
Ignoring power factor for motors
Motors, compressors, and other inductive loads have a power factor below 1.0, which means they draw more amps than Watts / Volts suggests. A motor with PF of 0.85 draws about 18% more current.
Running too many appliances on one circuit
Add the individual amperages of every device on the circuit. Two 12-amp appliances on a 20-amp circuit will trip the breaker. Spread high-draw devices across dedicated circuits.
Important Disclaimer
These estimates are for planning purposes only. Actual costs vary by location, material availability, and project complexity. Always get at least 3 local quotes. This calculator does not replace professional advice.