Convert watts, amps and volts in any direction with P = V × I. Works for DC battery systems and single-phase AC.
Watts ÷ (volts × power factor) for AC. Leave at 1.0 if unsure or for resistive loads.
Uses the ideal relationship P = V × I (× power factor for AC). Real circuits also lose a little to wiring resistance and, on AC, to reactive power; treat the result as a close planning figure, not a metered measurement.
These three are tied together by one of the most useful equations in electricity, the power law:
Watts = Volts × Amps (P = V × I)
Rearrange it and you can find any one value from the other two:
Amps = Watts ÷ Volts — "watts to amps"
Watts = Volts × Amps — "amps to watts"
Volts = Watts ÷ Amps
DC vs AC
On a DC circuit — a battery, a solar panel, a 12 V appliance — the plain power law applies directly. On a single-phase AC circuit you also multiply by the power factor, the fraction of the supplied current that does useful work:
Watts = Volts × Amps × PF
Resistive loads (heaters, kettles, incandescent bulbs, most switch-mode power supplies) have a power factor near 1.0, so they behave like the simple formula. Motors and other inductive loads run lower — often 0.6 to 0.85 — and therefore draw more current than their watt rating alone implies. That extra current still has to pass through your breaker, wiring and inverter.
A worked example
You want to run a 600 W load and need to know the current at different voltages:
At 12 V DC: 600 ÷ 12 = 50 A — needs heavy cable and a 60 A+ fuse
At 24 V DC: 600 ÷ 24 = 25 A
At 120 V AC (resistive): 600 ÷ 120 = 5 A
At 240 V AC (resistive): 600 ÷ 240 = 2.5 A
Same power, wildly different current. This is the core reason large off-grid systems run at 24 V or 48 V rather than 12 V: moving the same energy at higher voltage means lower current, which means thinner wire, smaller fuses and lower resistive losses.
Why high DC current is a problem
Current, not power, is what sizes your wiring and fuses. A 2,000 W inverter pulling from a 12 V bank draws around 185 A on the DC side — that calls for very thick, expensive cable (roughly 1/0 AWG or larger) and a large fuse. The same inverter on 48 V draws closer to 46 A and uses far smaller cable. If your amp figures look alarmingly high, that's usually a sign your system voltage is too low for the load.
Common voltages
Circuit
Nominal voltage
Small DC / battery bank
12 V
Mid off-grid bank
24 V
Large off-grid / home bank
48 V
North American mains
120 V (240 V for large appliances)
UK / EU / most of world mains
230–240 V
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Frequently asked questions
How do you convert watts to amps?
Divide watts by volts: amps = watts ÷ volts. For example, a 600 W load on a 12 V battery draws 600 ÷ 12 = 50 amps. For single-phase AC, divide also by the power factor: amps = watts ÷ (volts × power factor).
How do you convert amps to watts?
Multiply amps by volts: watts = volts × amps. On a 120 V circuit, 5 amps is 120 × 5 = 600 watts. For single-phase AC with an inductive load, multiply by the power factor too: watts = volts × amps × power factor.
What voltage should I use?
Use the voltage of the circuit the load is on. For DC battery systems that's the nominal bank voltage (12 V, 24 V or 48 V). For household AC it's your mains voltage — about 120 V in North America and 230–240 V in much of the rest of the world. The amp figure changes a lot with voltage.
What is power factor and when does it matter?
Power factor is the ratio of real power (watts) to apparent power (volt-amps) on an AC circuit. Resistive loads like heaters and incandescent bulbs sit at 1.0. Motors and other inductive loads run lower — often 0.6 to 0.85 — so they draw more current than their wattage suggests. For DC circuits power factor doesn't apply; leave it at 1.
Why does my 12V system pull such high amps?
Because amps = watts ÷ volts, low voltage means high current for the same power. A 1,000 W load is only about 4.3 A at 230 V, but 83 A at 12 V. High DC current needs thick, expensive cable and large fuses — which is why bigger off-grid systems move to 24 V or 48 V.