Watts to Amps Calculator
Enter power in watts and voltage in volts to get current in amps and resistance in ohms — the values you need to size fuses, cables, and circuit breakers correctly.
DC and resistive AC loads
The formula I = P ÷ V is exact for DC circuits and for AC loads with a unity power factor — resistive heaters, incandescent bulbs, and most heating elements.
AC motors and electronics draw more
Inductive loads such as motors, compressors, and switching power supplies have a power factor below 1, so the actual current they draw is higher than this calculator shows. See the limitations section for details.
What is Watt's law?
The relationship between power, voltage, and current
Watt's law states that electrical power equals voltage multiplied by current: P = V × I. Rearranging gives the current for a known power and voltage: I = P ÷ V. This is the fundamental equation used to work out how many amps an appliance draws from the mains, how to choose the right fuse rating, and how thick a cable needs to be for a given load. The same relationship also yields resistance via Ohm's law: R = V² ÷ P.
Enter the power in watts and the voltage in volts to get the current in amps and the resistance in ohms instantly.
Divide the power by the voltage to get the current, then square the voltage and divide by the power to get the resistance.
I = P ÷ V R = V² ÷ PAt 230 V (European mains), a 100 W bulb draws 100 ÷ 230 ≈ 0.43 A. A 2,300 W electric heater on the same supply draws 2,300 ÷ 230 = 10 A exactly — enough to trip a 10 A breaker at full load. On the North American 120 V grid the same 100 W device draws 100 ÷ 120 ≈ 0.83 A, and a 1,500 W appliance draws 1,500 ÷ 120 = 12.5 A.
The current figure tells you how much electrical charge flows through the circuit every second. For household appliances, most standard wall sockets in Europe are rated at 16 A, while North American outlets are typically 15 A or 20 A. A result well below those limits means the load is safe for a standard circuit; a result above them means a dedicated circuit with appropriate wiring and a correctly rated breaker is required. As a rule of thumb, keep the continuous load on a circuit below 80 % of its rated amperage — so a 16 A circuit should carry no more than about 13 A continuously. The resistance figure reflects the effective impedance of the load at the stated power and voltage; it is most useful when checking that a heating element or resistive load is operating within its design specification.
This calculator gives the resistive-load estimate only.
AC loads with a power factor below 1 draw more current
Motors, compressors, fluorescent lighting, and most switching power supplies are inductive or capacitive loads with a power factor less than 1. Their true current draw is: I = P ÷ (V × power factor). For example, a 1,000 W motor with a power factor of 0.8 at 230 V draws 1,000 ÷ (230 × 0.8) ≈ 5.43 A — not the 4.35 A this calculator would show. Always check the device's nameplate or data sheet for the rated current before sizing protective devices.