Watts to amps calculator
Convert watts to amps instantly, for 230 V UK mains, 12 V DC and 400 V three-phase, with power factor handled for you. Free, no sign-up, no faff.
- Supply–
Guidance only. This gives you load current. Sizing a device or cable also needs diversity, installation method and voltage drop, run those through the cable size calculator.
How to convert watts to amps
To convert watts to amps, divide the watts by the voltage: amps = watts ÷ volts. On a UK 230 V supply, a 3,000 W load is 3000 ÷ 230 = 13 A, which is exactly why 3 kW is the ceiling for anything on a plug. For motors and other inductive loads, divide by voltage × power factor instead.
Watts tell you how much power a load uses. Amps tell you how much current it pulls to deliver that power. The voltage sits between the two as the exchange rate, which is why the same 1,000 W load is a polite 4.35 A on UK mains but a chunky 83 A at 12 V. Same power, wildly different current, and wildly different cable.
The three formulas
Pick the one that matches your supply:
DC: I = W ÷ V
Single-phase AC: I = W ÷ (V × pf)
Three-phase AC: I = W ÷ (1.732 × V × pf)
For three-phase, V is the 400 V line voltage and 1.732 is the square root of 3. The pf is power factor: use 1 for resistive loads like heaters and lighting, and the nameplate figure for motors, usually somewhere between 0.8 and 0.9.
Step by step, straight off the rating plate
- Find the wattage on the appliance rating plate, usually on the back or underside near the serial number.
- Pick your voltage: 230 V for UK mains, 12 V or 24 V for battery kit, 400 V for three-phase.
- Set the power factor: 1 for anything that just makes heat or light, the nameplate figure (usually 0.8 to 0.9) for motors. DC ignores it entirely.
- Divide the watts by voltage × power factor, adding the 1.732 for three-phase, and you have your amps.
- Sanity-check the answer against whatever's carrying it: the 13 A plug, the flex, the breaker. That last step is the one that keeps things from melting.
The 230 V shortcut worth memorising
For UK mains at power factor 1, just divide the watts by 230. A 2 kW fan heater is 2000 ÷ 230 = 8.7 A. If your brain prefers multiplying, watts times 0.00435 gets you the same answer. Either way, "divide by 230" is the one conversion every electrician should be able to do standing in a loft.
Worked examples
A 900 W microwave on UK mains: 900 ÷ 230 = 3.9 A, happy on any socket circuit. A 120 W run of 12 V LED strip: 120 ÷ 12 = 10 A, which is why that "tiny" lighting job still wants proper cable and a proper fuse. And a 7.5 kW three-phase motor at 0.85 power factor: 7500 ÷ (1.732 × 400 × 0.85) = 12.7 A per phase. Notice the motor pulls more current than the watts alone suggest, that's the power factor doing its thing.
Watts to amps conversion table
| Watts | Amps at 230 V AC | Amps at 12 V DC |
|---|---|---|
| 100 W | 0.43 A | 8.3 A |
| 200 W | 0.87 A | 16.7 A |
| 300 W | 1.30 A | 25 A |
| 500 W | 2.17 A | 41.7 A |
| 700 W | 3.04 A | 58.3 A |
| 1000 W | 4.35 A | 83.3 A |
| 1500 W | 6.52 A | 125 A |
| 2000 W | 8.70 A | 166.7 A |
| 2200 W | 9.57 A | 183.3 A |
| 2500 W | 10.87 A | 208.3 A |
| 3000 W | 13.04 A | 250 A |
Why 3 kW is the magic number
Look at the bottom row. A UK 13 A plug tops out around 2,990 W at 230 V, so 3,000 W lands bang on the ceiling. That's why plug-in appliances cluster at 3 kW and never meaningfully above it, and why anything hungrier, showers, cookers, EV chargers, gets its own circuit.
The plug fuse follows the same maths. UK plug fuses (BS 1362) come in a range of ratings, but the two standard sizes you'll actually meet are 3 A and 13 A, and the usual guidance is a 3 A fuse for appliances up to about 700 W and a 13 A fuse above that. Do the watts to amps sum and the right fuse falls out on its own, though the manufacturer's stated size always wins.
Now look at the 12 V column, because it gets silly fast. Pushing 3 kW through a 12 V system means 250 A, which is welder territory. That's exactly why car, leisure and solar kit uses cables that look comically thick for the wattage involved. The wattage isn't the problem, the current is.
- Watts are power, amps are current, and the voltage decides the exchange rate between them. Change the voltage and the current changes with it.
- Low-voltage DC currents are huge per watt. Size leisure-battery and solar cable for the amps, not the watts, then sanity-check the run in the cable size calculator.
- For motors, use the nameplate power factor rather than assuming 1, otherwise you'll understate the current the circuit actually carries.
If your load is stamped in kilowatts, the kW to amps calculator does the same job without the mental zeros. Generators and transformers rated in kVA go through the kVA to amps calculator instead, and if you're juggling volts, amps and resistance in one problem, the Ohm's law calculator ties the whole lot together.
Watts to amps FAQs
How many amps is 3000 watts at 230 V?
13.04 A, or 13 A for everyday purposes. That number is no accident: it sits right on the practical limit of a UK 13 A plug, which is why 3 kW is the biggest load you'll find on a plug top. Anything meatier needs its own dedicated circuit, not an extension lead and a prayer.
How many amps is 1000 watts at 230 V?
4.35 A at power factor 1. That makes a tidy mental shortcut: every kW on UK mains is about 4.35 A, so 2 kW is 8.7 A and 3 kW is 13 A. Learn that one number and you can size up most plug-in kit in your head.
How many watts can a 13 amp plug handle?
About 2,990 W at 230 V, because 13 A times 230 V is 2,990 W. That's the reason kettles, fan heaters and plug-in ovens all cluster at 3 kW and never go meaningfully above it. Manufacturers design to the plug, not the other way round.
What size plug fuse do I need?
UK plug fuses (BS 1362) effectively come in two standard sizes, 3 A and 13 A. The usual guidance is 3 A for appliances up to about 700 W and 13 A above that, with the manufacturer's stated size always taking priority. Remember the fuse is there to protect the flex, not the appliance, so bigger is not better.
How do I convert watts to amps at 12 V?
Divide the watts by 12. A 240 W load at 12 V DC draws 20 A. Because the voltage is so low, the current per watt is enormous compared with mains, roughly 19 times higher, so battery, leisure and solar cabling has to be sized for the amps even when the wattage sounds trivial.
How do I convert watts to amps on three-phase?
Divide the watts by 1.732 × 400 × power factor. At unity power factor that works out at watts ÷ 693 or so, meaning a 10,000 W three-phase load draws about 14.4 A per phase. And it is per phase: the load is shared across three lines, not stacked on one.
Do I need to worry about power factor?
For resistive loads, no. Heaters, kettles and lighting run at power factor 1, so watts divided by volts gives you the current straight off. For motors, compressors and anything with a winding in it, yes: use the nameplate figure, typically 0.8 to 0.9. Ignore it and the real current will be higher than your sums, which is not the kind of surprise you want on a marginal circuit.
What is the difference between watts and VA?
Watts are real power, the work actually being done. VA (volt-amps) is apparent power, simply volts multiplied by amps. Power factor is the ratio between the two: at pf 1 they're identical, at pf 0.8 a 1,000 VA load only delivers 800 W of useful work. Generators and UPS kit are rated in VA, which is exactly why the kVA to amps calculator exists.
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