Amps and watts are not directly interchangeable
Amps measure current while watts measure power. Voltage is required to convert between them using the basic DC power relationship.
Convert amps to watts for DC
For example, 8 amps at 12 volts corresponds to 96 watts in a simple DC circuit.
Convert watts to amps for DC
A 240-watt load at 24 volts draws 10 amps under the idealized DC relationship.
Single-phase AC
For AC loads, real power can depend on power factor. When power factor is relevant, it must be included rather than assuming volts multiplied by amps equals real power.
Three-phase systems
Three-phase power calculations use different relationships from basic single-phase or DC calculations. The correct formula depends on the system configuration and the voltage being referenced.
Common mistakes
- Trying to convert watts to amps without knowing voltage.
- Ignoring power factor when it is relevant.
- Using a DC formula for a three-phase system.
- Using nominal voltage when the actual calculation requires a different system voltage.
These formulas are useful for basic estimation. Equipment ratings, circuit design and protective devices should be selected using the applicable technical requirements.