Use Ohm’s law: Amps = Volts ÷ Ohms
Use power and voltage: Amps = Watts ÷ Volts
Use power and resistance: Amps = square root of Watts ÷ Ohms
Measure current directly with an ammeter or multimeter set to current mode
For AC circuits, use the same formulas with RMS values
For three-phase power: Amps = Watts ÷ (Volts × 1.732 × Power Factor)
For DC circuits: Amps = Watts ÷ Volts
For batteries: Amps = load power ÷ battery voltage
For motors and inductive loads: include power factor when calculating from watts
Verify units before calculating: volts, watts, and ohms must match the formula used