Appliance Wattage Calculator

Compute an appliance's power draw from its voltage and amperage (P = V x A), then estimate how much energy it uses per day and what that costs per month and per year.

Quick Facts

Formula
Watts = Volts x Amps (P = V x I)
The same formula printed on most appliance nameplates and power supplies.
Circuit capacity
A 15A/120V circuit is rated for 1,800W
The NEC recommends capping continuous loads at 80% of a breaker's rating, or 1,440W on a 15A/120V circuit.

Your Results

Calculated
Power draw
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Watts = Volts x Amps
Daily energy use
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Kilowatt-hours per day
Estimated monthly cost
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Based on 30 days of use
Estimated annual cost
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Based on 365 days of use

Ready

Enter voltage, amperage, hours of use, and your electricity rate, then press Calculate.

Understanding Appliance Wattage

This tool converts an appliance's electrical nameplate ratings into a power draw, a daily energy estimate, and a running cost. Most appliances list a voltage and an amperage (or "current") rating rather than watts directly, so the calculator applies the basic electrical power formula: Watts = Volts x Amps (also written P = V x I). Once wattage is known, it is converted into energy over time and then into a dollar estimate.

The formulas

Four calculations run in sequence, each building on the last:

  • Power draw (watts): Volts x Amps. A 120V appliance drawing 8.3A uses about 996W.
  • Daily energy use (kWh/day): Watts x hours used per day, divided by 1000 (to convert watt-hours to kilowatt-hours).
  • Monthly cost: daily kWh x 30 days x your electricity rate ($/kWh).
  • Annual cost: daily kWh x 365 days x your electricity rate ($/kWh).

The 30- and 365-day figures are simplifying assumptions for a typical month and year; actual billing cycles vary slightly, and your utility's rate may include tiered pricing or fees not reflected in a flat $/kWh figure.

Where to find voltage and amperage

Both values are usually printed on a nameplate or sticker on the appliance itself, often near the power cord. Standard household circuits in the US run at 120V for most outlets and 240V for large appliances like electric dryers, ranges, and water heaters. If the nameplate already states wattage directly, you can skip the voltage/amperage math and enter that wattage's equivalent volts and amps (for example, 1000W at 120V is 8.3A).

Reading the circuit-capacity note

Wattage also matters for circuit safety. A standard 15A/120V household circuit is rated for 1,800W, and a 20A/120V circuit for 2,400W. The National Electrical Code recommends limiting continuous loads (running 3+ hours) to 80% of a circuit's rating — 1,440W and 1,920W respectively — to leave a safety margin. High-draw appliances such as space heaters, microwaves, and window air conditioners are common culprits for tripped breakers when combined with other loads on the same circuit.

Frequently Asked Questions

How do I calculate appliance wattage from the nameplate?
Most appliance nameplates list voltage (V) and amperage (A) rather than watts. Multiply the two using the formula Watts = Volts x Amps. For example, an appliance rated at 120V and 8.3A draws about 996 watts. If the nameplate already lists watts directly, you can use that figure instead of multiplying.
How do I estimate the cost of running an appliance?
Convert wattage to daily energy use in kilowatt-hours: multiply watts by hours used per day, then divide by 1000. Multiply that daily kWh figure by your electricity rate (dollars per kWh) and by the number of days to get a cost estimate, such as 30 days for a monthly figure or 365 for an annual one.
What size circuit does an appliance need?
A standard 15A/120V household circuit is rated for 1800 watts, and the National Electrical Code recommends keeping continuous loads to 80% of that rating, or about 1440 watts. A 20A/120V circuit is rated for 2400 watts (1920 watts continuous). High-wattage appliances such as space heaters, dryers, or ovens often need a dedicated or 240V circuit.
Why does my utility bill differ from this estimate?
This calculator assumes constant wattage for the full number of hours entered, but many appliances (refrigerators, HVAC systems, dishwashers) cycle on and off and draw less than their rated wattage on average. Treat the result as an estimate based on the nameplate rating and your entered usage pattern, not a guaranteed bill amount.

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