Amps to Watts Calculator

About the Amps to Watts Calculator

Converting amps to watts is one of the most common electrical calculations. Amps (amperes) measure the flow rate of electrical current, while watts measure the rate of energy consumption or production. The conversion requires knowing the voltage and, for AC circuits, the power factor.

For DC circuits and purely resistive AC loads, the formula is simply: Watts = Amps × Volts. For AC circuits with inductive or capacitive loads, the power factor must be included: Watts = Amps × Volts × Power Factor. Common scenarios include determining how many watts an appliance draws for energy cost calculations or verifying that a circuit can handle a load.

This calculator handles both single-phase AC and DC conversions. Enter the amperage and voltage to get watts, or use it to verify that an appliance's wattage matches its amp draw on a specific circuit.

Integrating this calculation into regular energy reviews ensures that conservation strategies are grounded in measured data rather than assumptions about building performance and usage patterns.

When This Page Helps

Understanding the amps-to-watts relationship is essential for circuit design, energy cost estimation, and ensuring electrical safety. It gives instant, accurate conversion for any voltage and power factor combination.

How to Use the Inputs

1. Enter the current in amps.
2. Enter the voltage (e.g., 120V, 240V, 12V).
3. Enter the power factor (1.0 for DC or resistive AC loads).
4. View the result in watts and kilowatts.
5. Use the wattage for energy cost calculations.
6. Verify against appliance nameplate ratings.

Example Calculation

Tips & Best Practices

• For DC circuits, power factor is always 1.0.
• For AC motors, use PF of 0.80–0.90 for accurate watt calculation.
• A 15A/120V circuit can supply 1,800W maximum.
• Never exceed 80% of circuit capacity for continuous loads (1,440W on 15A).
• Check the nameplate amps, not the startup/inrush amps, for steady-state calculations.
• For three-phase, multiply by √3 (use the three-phase power calculator).

Understanding Amps, Volts, and Watts

Amps (current) = the rate of electron flow. Volts (voltage) = the electrical pressure driving the flow. Watts (power) = the rate of energy use. The relationship is W = A × V. Think of water: amps = flow rate (gallons/min), volts = water pressure (PSI), watts = power delivered.

Common Amperage Values

Small electronics: 0.1–0.5A at 120V. LED bulbs: 0.1A. Coffee maker: 8‒10A. Space heater: 12.5A. Hair dryer: 12–15A. Window AC: 5‒15A. Electric dryer: 24‒30A at 240V. Electric range: 40–50A at 240V.

Circuit Capacity Planning

Knowing the amps-to-watts conversion helps plan electrical circuits. The NEC limits continuous loads to 80% of the breaker rating. A 20A circuit can continuously supply 16A or 1,920W at 120V. Adding up all loads on a circuit ensures you don't exceed this limit.

Frequently Asked Questions

• How many watts is 1 amp at 120V?

  1 amp at 120V equals 120 watts (for resistive loads with PF = 1.0). For inductive loads with PF = 0.85, 1 amp at 120V equals 102 watts of real power.

• How do I convert amps to watts at 240V?

  Multiply amps by 240 and by the power factor. For example: 20A × 240V × 1.0 = 4,800W. For a motor load: 20A × 240V × 0.85 = 4,080W.

• What is power factor?

  Power factor is a number between 0 and 1 that represents how efficiently current is converted to useful power. Resistive loads (heaters, incandescent bulbs) have PF = 1.0. Inductive loads (motors, compressors) typically have PF = 0.70–0.95.

• Why do I need to know watts from amps?

  Watts tell you the actual power consumption, which determines energy cost (kWh), heat generation, and whether a circuit or generator has sufficient capacity. Amps alone don't tell you the power without knowing the voltage.

• How do I calculate amps if I know watts?

  Amps = Watts / (Volts × PF). For a 1,500W heater on 120V: 1,500 / (120 × 1.0) = 12.5 amps. This calculation determines what circuit and wire size you need.

• Are amps the same for 120V and 240V?

  No. The same wattage draws half the amps at 240V compared to 120V. A 4,800W load draws 40A at 120V but only 20A at 240V. This is why high-wattage appliances use 240V — smaller wires and breakers are needed.