Watts to Amps Calculator
Convert watts to amps using voltage, power type, power factor, and a planning buffer. This is useful for basic battery, inverter, power supply, extension cord, and low-voltage project planning.
Enter Your Numbers
Your Results
Estimated current
With buffer
Formula type
Input power
How to Use This Watts to Amps Calculator
Enter the device wattage and voltage, then choose whether the setup is DC, single-phase AC, or three-phase AC. For AC loads, use the power factor if you know it. If you do not know the power factor, use this calculator as a rough planning estimate only.
The buffer field adds extra current capacity to the result. This helps avoid sizing a power supply, inverter, or low-voltage setup too close to the exact calculated number.
Formula Used
Single-phase AC amps = watts ÷ (volts × power factor)
Three-phase AC amps = watts ÷ (1.732 × volts × power factor)
Buffered amps = calculated amps × (1 + buffer %)
Example Calculation
A 500-watt device on 120V single-phase AC with a power factor of 1.0 uses about:
With a 20% planning buffer, the estimated planning current becomes about 5 amps.
Common Mistakes
- Using startup surge instead of running watts, or ignoring startup surge completely.
- Assuming watts and amps are interchangeable without voltage.
- Forgetting inverter losses when converting battery power to AC power.
- Using a power supply or inverter right at its maximum rating.
- Ignoring wire length, voltage drop, heat, connectors, and manufacturer limits.
Important Safety Note
Use this calculator for planning only. Do not use it as permission to overload a wire, outlet, extension cord, inverter, power supply, breaker, battery, or circuit. For mains wiring, permanent circuits, breaker panels, damaged cords, heat, sparks, burning smells, or code-sensitive work, stop and contact a qualified professional.