Watt Calculator - Calculate Watts, Amps & Volts
Calculate watts, amps, or volts from any two values using W = V × I. Free online electrical power calculator.
How is Power (Watts) Calculated?
Electrical power in watts is calculated by multiplying voltage by current. Leave any one of the three fields (watts, amps, or volts) blank and fill in the other two to calculate the missing value. This uses the fundamental electrical formulas W = V × I, V = W / I, and I = W / V.
Example
A device draws 2 amps at 120 volts. Power = 120 × 2 = 240 watts. The resistance is 120 / 2 = 60 Ω. Running this device for one hour consumes 240 watt-hours (Wh) of energy.
Common Use Cases
- Figuring out the wattage of an appliance when you only know its voltage and current draw.
- Determining how much current a device needs given its power rating and supply voltage.
- Calculating energy cost — multiply watt-hours by your electricity rate to estimate running cost.
FAQs
What is the difference between watts and watt-hours?
Watts (W) measure instantaneous power — how fast energy is being used. Watt-hours (Wh) measure energy consumed over time. A 100W bulb running for 3 hours uses 300 Wh of energy.
Can I use this for DC and AC circuits?
The basic formulas W = V × I work for DC circuits and for AC circuits with a pure resistive load (power factor of 1). For AC circuits with reactive loads, you would need to account for the power factor, which this calculator does not include.
What is resistance and why is it shown?
Resistance (measured in ohms, Ω) is the opposition to current flow. It is calculated using Ohm's law R = V / I and is useful for understanding the electrical characteristics of the circuit.