Watts, amps & volts: conversions explained

Watts, amps and volts lock together through one relationship: watts = volts × amps. Know any two and you can work out the third. The sections below cover the formulas the calculator runs, a 230 V reference table, and the 12 V cases where sizing matters most.

How to convert watts to amps

Divide watts by volts. For anything that plugs into a wall socket in Australia, that means dividing by 230:

• 1,000 W ÷ 230 V = 4.3 A
• 2,400 W ÷ 230 V = 10.4 A, a full 10 A circuit (this is why kettles top out around 2,400 W)

Power factor only matters on AC, and only for some loads. Resistive appliances (kettles, heaters, ovens and most lighting) sit at or near 1, so you can leave it out. Motors, pumps and air conditioners typically sit between 0.8 and 0.95, which pushes the current up for the same wattage: a 2,400 W pump at 0.8 draws 13 A, not 10.4 A.

Three-phase supplies (400 V between phases in Australia) split the load across three conductors, so each phase carries far less current for the same wattage. A 10,000 W three-phase machine at 0.9 power factor draws about 16 A per phase: 10,000 ÷ (1.732 × 400 × 0.9).

How to convert amps to watts

Multiply amps by volts. A 10 A load on a 230 V circuit is drawing up to 2,300 W. For AC gear with a power factor below 1, multiply by that too: 10 A × 230 V × 0.9 = 2,070 W. On three-phase, multiply by 1.732 as well: 20 A at 400 V and 0.9 power factor is 20 × 1.732 × 400 × 0.9, about 12,470 W.

This is the direction you use when sizing what a circuit can carry: the amp rating is fixed by the breaker and the wiring, and the watts tell you what you can run on it.

Watts to amps at 230 V: reference table

Current draw for common appliance wattages on a standard 230 V single-phase supply, assuming a power factor of 1. Figures are rounded.

Watts to amps at 12 V

Low-voltage DC gear runs the same division at 12 V, and the currents are roughly 19 times higher for the same wattage. A 60 W LED strip draws 0.26 A at 230 V but 5 A at 12 V; a 120 W car fridge pulls 10 A from a 12 V battery. That current, not the wattage, is what sizes the cable, the fuse and the power supply, so do this conversion before you buy an LED driver or wire up a caravan.

The same maths covers 24 V and 48 V systems: halve or quarter the 12 V figure.

Volts to watts and amps to volts

The same relationship rearranges to answer the other two questions:

In practice you rarely calculate the voltage; you look it up (230 V mains, 12 V or 24 V low-voltage, 400 V three-phase) and solve for current or power instead.