Watts to amps 120V: why voltage matters
Watts describe real electrical power, whereas amperes describe current. A current cannot be calculated from watts without knowing the voltage and the kind of circuit. Enter the power in watts and the voltage that actually applies to the load. In a direct-current circuit the relation is P = V × I, so current is watts divided by volts. For example, a 1200 W DC load supplied at 120 V draws 10 A in this simplified steady-state calculation. A device rated at the same 1200 W but supplied at a different voltage draws a different current. The tool does not infer voltage from your country or from an appliance name.
Single-phase AC and power factor
For a single-phase alternating-current load, use real power P = V × I × power factor. If a 1200 W load operates at 120 V with a power factor of 0.8, its current is 1200 ÷ (120 × 0.8) = 12.5 A, not 10 A. Power factor is a ratio between zero and one and must reflect the equipment and operating condition. A purely resistive idealized load may be close to one, while motors and electronic supplies can differ. Do not confuse real power in watts with apparent power in volt-amperes; substituting a VA label into the watts field changes the meaning of the formula. A missing power factor should not be silently guessed for a real installation.
Balanced three-phase calculation
For a balanced three-phase AC load, the calculator uses P = √3 × V × I × power factor. The voltage field must contain line-to-line RMS voltage, not the phase-to-neutral value. A 6000 W balanced load on a 400 V line-to-line system with power factor 0.8 gives about 10.83 A of line current. This formula assumes the three phases share the load equally. It is not suitable for a single phase carrying most of the current, a strongly unbalanced system or an installation with unknown voltage conventions. Check the equipment plate and wiring diagram before choosing the three-phase option. The square-root-of-three factor is not used for DC or single-phase circuits.
Reading the result responsibly
The displayed amperes estimate operating current from the values you entered. It does not calculate inrush current when a motor starts, protective-device settings, conductor size, voltage drop or safe capacity of a socket. Actual power and power factor can change as equipment cycles or its load varies. Use measured values when comparing a device to a specification, and consult a qualified professional and applicable electrical rules for installation decisions. If the result looks implausible, first check whether the source lists W, kW or VA, whether the voltage is line-to-line for three-phase, and whether the power factor was entered as 0.8 rather than 80. This browser calculation sends no entered values to a server.