A 1,150 W load on 230 V single-phase
- Input
- Power = 1150 W, Voltage = 230 V, Single-phase, PF = 1
- Working
- I = P ÷ (V × PF) = 1150 ÷ 230 = 5 A exactly.
- Result
- Current = 5 A
Watts to Amps Converter
Convert watts to amps or amps to watts for single-phase, DC and three-phase circuits, with voltage and power factor — plus a table at 120, 230 and 400 volts. Runs entirely in your browser — your numbers never leave this device.
Convert
Phase
Current
5 A
Single-phase
- Power factor
- 1
- Phase
- Single
| Voltage (V) | Current (A) |
|---|---|
| 120 | 9.58 |
| 230 | 5 |
| 400 | 2.88 |
How it works
Single-phase / DC: I = P ÷ (V × PF), P = V × I × PF | Three-phase: I = P ÷ (√3 × V × PF), P = √3 × V × I × PF, V = line-to-line voltage
| Circuit | Amps from watts | Watts from amps |
|---|---|---|
| DC / resistive | I = P ÷ V | P = V × I |
| Single-phase AC | I = P ÷ (V × PF) | P = V × I × PF |
| Three-phase AC | I = P ÷ (√3 × V × PF) | P = √3 × V × I × PF |
Power, voltage and current are linked by P = V × I, so current is power divided by voltage — once the two complications are handled. The first is power factor: on AC, inductive and capacitive loads draw current that does no work, and only the fraction PF of V × I is real power, so the formula divides by PF as well. Resistive loads and DC have a power factor of 1; motors typically sit between 0.8 and 0.9, and the nameplate PF is the figure to use when there is one. The second complication is three-phase power, where the total is √3 × line-to-line voltage × current × PF — the √3 appears because the three phases are 120° apart, and the voltage to enter is the line-to-line figure (400 V on a typical 400/230 V system), not the phase voltage.
The converter runs in both directions — watts to amps for sizing a breaker or cable against a known load, amps to watts for reading what a measured or nameplate current actually delivers — and prints the entered wattage at 120, 230 and 400 V alongside, the three voltages most nameplates and supplies use. Keep the chain in mind: amps from here feed the Voltage Drop Calculator for the cable run, and the wattage feeds the Electricity Cost Calculator for the running cost.
Worked examples
A 10 kW three-phase load on 400 V
- Input
- Power = 10,000 W, Voltage = 400 V (line-to-line), Three-phase, PF = 0.85
- Working
- I = 10,000 ÷ (√3 × 400 × 0.85) = 10,000 ÷ 588.90 = 16.98 A per phase.
- Result
- Current = 16.98 A
Watts from a 16 A three-phase current
- Input
- Current = 16 A, Voltage = 400 V, Three-phase, PF = 0.9
- Working
- P = √3 × V × I × PF = 1.732 × 400 × 16 × 0.9 = 9,976.61 W — just under 10 kW delivered.
- Result
- Power = 9,976.61 W
Frequently asked questions
What power factor should I enter?
1 for DC and for purely resistive AC loads — heaters, kettles, incandescent lamps. For motors, pumps and compressors use the nameplate power factor, commonly 0.8–0.9; for a mixed or unknown load, 0.9 is a common planning assumption. A lower power factor means more current for the same watts, which is why the field matters for cable and breaker sizing.
Which voltage do I enter for three-phase?
The line-to-line voltage — 400 V on a 400/230 V system, 480 V on a 480/277 V system. The √3 in the formula already converts between line and phase quantities; entering the 230 V phase voltage into the three-phase formula would understate the power by a factor of √3.
Why does a 2,000 W heater draw different amps in different countries?
Because current is watts divided by voltage: the same 2,000 W is 16.67 A at 120 V, 8.70 A at 230 V and 5 A at 400 V single-phase. That is exactly why the reference table prints the entered wattage at 120, 230 and 400 V — the appliance's power is fixed, but the current its cable and breaker must carry is not.
Can I convert amps to watts with this too?
Yes — use the direction switch. Amps to watts runs the same formulas in reverse: P = V × I × PF single-phase, and P = √3 × V × I × PF three-phase, as the third worked example shows (16 A at 400 V and PF 0.9 delivers 9,976.61 W).
Is the amps figure the breaker size I need?
Not directly. This converter gives the load's actual current; breaker and cable sizing then apply your code's rules — continuous-load factors, ambient temperature, grouping and protective-device ratings — on top of it. Use this figure as the starting point and the Voltage Drop Calculator for the run, then size protection per your local code.
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