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Calculate watts, volts and amps for direct current

Enter two known values and calculate the third. The calculator links power in watts, voltage in volts and current in amps for direct current.

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The voltage across the load.

V

The current through the circuit.

A

Applies to direct current (DC). The result is not an approval of cable, fuse or installation.

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Worked example
  • Calculate: Power (watts)
  • Voltage: 12 V
  • Current: 5 A

Result

Power

60 W

Working

  1. P = U × I
    12 V × 5 A = 60 W

What do watts, volts and amps describe?

Watts give the power, volts give the voltage and amps give the current. The quantities describe different aspects of the same circuit. If you know two of them, the calculator can find the third.

First choose which quantity is missing. To find the power, you need to know the voltage and the current. To find the current or the voltage, you need to know the power and the other quantity. The calculation applies to direct current, also called DC.

The formula for power with direct current

Power is calculated with P = U × I. U is the voltage and I is the current. To find the voltage, U = P / I is used. To find the current, I = P / U is used.

This relationship can be used for a DC circuit. The result is not an approval of cable, fuse or installation. For alternating current, use the AC power calculator, which also includes the power factor.

Example with 12 V and 5 A

The voltage is 12 V and the current is 5 A. The power is 12 V × 5 A = 60 W. If you want to check the current from the result, the reverse calculation gives 60 W / 12 V = 5 A.