Quick answer
Watts = volts × amps. A 2,000 W kettle on 230 V draws 8.7 A; on 120 V it draws 16.7 A. For AC motors, multiply by the power factor as well.
How to use the Electrical Power Calculator
- Choose the circuit type: DC (batteries, solar, electronics), AC single-phase (normal household sockets) or AC three-phase.
- Enter any two known values, for example power and voltage.
- For AC, enter the power factor. Use 1 for resistive loads like kettles and heaters.
- Press Calculate to get the other values.
Example
How much current does a 2,000 W kettle draw on a 230 V socket?
I = P ÷ (V × PF) = 2000 ÷ (230 × 1) = 8.7 A
On a 120 V outlet the same kettle would draw 2000 ÷ 120 = 16.7 A, which is why high-power appliances in North America are often limited to about 1,500 W.
Three-phase example: an 11 kW motor on 400 V with a power factor of 0.85 draws 11000 ÷ (√3 × 400 × 0.85) ≈ 18.7 A.
How it works
| Circuit | Real power | Current |
|---|---|---|
| DC | P = V × I | I = P ÷ V |
| AC single-phase | P = V × I × PF | I = P ÷ (V × PF) |
| AC three-phase | P = √3 × VL × I × PF | I = P ÷ (√3 × VL × PF) |
In DC mode you can also use resistance: P = I² × R and P = V² ÷ R.
For AC loads, the calculator also shows apparent power S in volt-amperes (VA), which sizes generators, UPS units and transformers, and reactive power Q in var. With a power factor of 1, apparent and real power are equal.
For three-phase systems, enter the line-to-line voltage, such as 400 V in Europe or 208/480 V in North America.
Quick reference: typical appliance power
- Kettle: 1,800-3,000 W (Europe), 1,200-1,500 W (North America).
- Microwave: 800-1,200 W of cooking power, but it draws roughly 1,200-1,700 W from the socket.
- Laptop charger: 45-100 W. Gaming PC under load: 300-600 W.
- Refrigerator: about 100-200 W while the compressor runs, but much less on average because it cycles on and off.
- Rule of thumb for sockets: on 230 V, every 1,000 W draws about 4.3 A. On 120 V, every 1,000 W draws about 8.3 A.
Frequently asked questions
How do I convert watts to amps?
Divide watts by volts (and by the power factor for AC): amps = watts ÷ volts. A 1,200 W microwave on 120 V draws about 10 A; on 230 V it draws about 5.2 A.
What is power factor?
The ratio of real power (watts) to apparent power (volt-amperes). Resistive loads have a power factor of 1. Motors and some power supplies have lower values, so they draw more current for the same real power.
What's the difference between kW and kVA?
kW is real power that does useful work. kVA is apparent power, which includes the reactive part. kW = kVA × power factor. Generators and UPS units are often rated in kVA.
What voltage should I use for three-phase?
Use the line-to-line voltage: 400 V in most of Europe, 415 V in Australia, 208 V or 480 V in North America.
How many watts can a 13 A or 16 A socket supply?
Roughly 230 V × 13 A ≈ 3 kW (UK) and 230 V × 16 A ≈ 3.7 kW (much of Europe). For continuous loads, stay below these limits.