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Watts to Amps Converter

Calculate current draw in amps from a device's power rating and voltage.

Result

Current
12.5 A

Based on the power formula P = V × I, rearranged to I = P ÷ V. This assumes a resistive AC load or DC circuit; for AC circuits with a power factor below 1 (like motors), actual current draw will be higher.

About the Watts to Amps

This calculator estimates how many amps of current a device draws, based on its power rating in watts and its operating voltage, using the basic relationship between power, voltage, and current. It is commonly used when sizing a circuit breaker, extension cord, or power strip for a known-wattage appliance.

How It Works

Enter a device's power draw in watts and the circuit voltage. The calculator divides watts by voltage to produce the current in amps, and if voltage is entered as zero it substitutes a value of 1 so the division still returns a number instead of an error.

Current (A) = Power (W) / Voltage (V), a rearrangement of the power formula P = V x I.

Formula & Methodology

This is a direct algebraic rearrangement of the power formula. For a 1,500-watt appliance on a 120-volt household circuit, dividing 1,500 by 120 gives 12.5 amps of current draw, close to the 15-amp limit of a typical residential breaker.

Examples

Sizing a Space Heater Circuit

The calculator's default inputs of 1,500 watts at 120 volts return 12.5 amps, just under the 15-amp rating of a standard US household outlet circuit.

A 3,000-Watt European Appliance

Entering 3,000 watts at 230 volts, a typical EU household voltage, returns about 13.04 amps, showing why the same wattage device draws noticeably less current on a higher-voltage system.

Advantages

  • Converts a wattage rating printed on almost every appliance into the amperage figure needed for breaker and wiring size decisions
  • Makes it easy to compare current draw across different regional voltage standards, such as 120V versus 230V
  • Uses a single, transparent formula that is easy to sanity-check against a device's own nameplate rating

Common Mistakes

  • Applying this resistive-load formula to a motor, compressor, or other inductive load and assuming the result is the full actual current draw, when the real figure can be meaningfully higher
  • Confusing running, steady-state wattage with a device's peak or surge wattage, which can be several times higher for a brief moment at startup
  • Sizing a breaker or cord to exactly the calculated amperage instead of leaving headroom, when standard electrical practice calls for a safety margin below a circuit's rated capacity

Edge Cases to Watch For

  • The formula assumes a power factor of 1, meaning all delivered power does useful work with no phase difference between voltage and current; motors, compressors, and other inductive AC loads have a power factor below 1 and will draw more real current than this result shows.
  • A voltage of exactly zero is replaced with 1 in the calculation rather than producing an infinite or undefined result, which will silently return an unrealistic amperage if voltage is left blank or mistyped as zero.
  • The result is a steady-state average draw, not the brief, higher inrush current many motors and compressors pull for a moment at startup.

Common Use Cases

  • Homeowners checking whether several appliances plugged into one circuit will exceed its breaker rating
  • People selecting an extension cord or power strip with an adequate amp rating for a given device
  • Anyone comparing how the same wattage appliance behaves differently on 120V versus 230V/240V electrical systems
Written & fact-checked by the Calculateus TeamLast updated August 5, 2026How we verify our formulas

Frequently asked questions

Why might my actual amp draw be higher than this calculation?

This formula assumes a power factor of 1 (all power does useful work), but motors, compressors and some electronics have a power factor below 1, meaning they draw more current than the watts-to-volts formula alone would suggest - check the device's nameplate amperage rating when precision matters, like sizing a breaker.

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Conclusion

Current draw is what actually determines wiring and breaker requirements, even though appliances are almost always labeled in watts. This calculator bridges that gap with the standard power formula, while flagging that inductive loads and startup surges can push real-world current above the calculated figure.

References