How do you convert watts to amps?

Divide watts by volts. Amps = Watts ÷ Volts. At 120V, a 1,200W appliance draws 10A. At 12V, the same 1,200W draws 100A — which is why high-power DC systems use 48V to keep current (and wire size) manageable.

What is the formula to convert amps back to watts?

Watts = Amps × Volts. For example, a 15A circuit at 120V can supply up to 1,800W. For safety, NEC recommends loading circuits to no more than 80% of breaker rating on continuous loads, so a 15A circuit should carry no more than 12A (1,440W) continuously.

How many amps does a 1,500W space heater draw?

A 1,500W space heater at 120V draws 12.5A (1,500 ÷ 120 = 12.5). This is right at the NEC 80% continuous load limit for a 15A circuit. Running two 1,500W heaters on the same 15A circuit will trip the breaker — each heater should ideally be on its own 15A or 20A circuit.

Quick answer: A 1,200 W appliance on a 120 V circuit draws 10 amps; on 240 V it draws 5 amps. Higher voltage means lower amperage for the same power.

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Watts to Amps Calculator

Convert watts to amps at any voltage — 120V, 240V, 12V, 24V, or 48V. Instant result, no sign-up required.

Watts / Amps Converter

Watts (W)

Voltage

Result

12.50 A

12.50 A × 120 V = 1,500 W

How we calculate watts to amps

Watts, amps, and volts are related by Ohm's Law. Dividing power by voltage gives current — the value needed for sizing breakers, fuses, wire gauge, and charge controllers.

Amps = Watts ÷ Volts

Always add a 20–25% safety margin above the calculated amperage before selecting a breaker or wire size for continuous loads.

Frequently Asked Questions

How do you convert watts to amps?: Divide watts by volts. Amps = Watts ÷ Volts. At 120V, a 1,200W appliance draws 10A. At 12V, the same 1,200W draws 100A — which is why high-power DC systems use 48V to keep current (and wire size) manageable.
What is the formula to convert amps back to watts?: Watts = Amps × Volts. For example, a 15A circuit at 120V can supply up to 1,800W. For safety, NEC recommends loading circuits to no more than 80% of breaker rating on continuous loads, so a 15A circuit should carry no more than 12A (1,440W) continuously.
How many amps does a 1,500W space heater draw?: A 1,500W space heater at 120V draws 12.5A (1,500 ÷ 120 = 12.5). This is right at the NEC 80% continuous load limit for a 15A circuit. Running two 1,500W heaters on the same 15A circuit will trip the breaker — each heater should ideally be on its own 15A or 20A circuit.

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Watts to Amps Calculator

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Reviewed April 2026

Methodology and source note

PowerSizing calculators use shared formulas, documented assumptions, and current planning inputs that are summarized on the methodology page. Use these tools for first-pass planning, comparison, and sanity checks, then confirm local code, pricing, utility tariff, and installer specifics before you buy equipment.