PowerCalcLab

Power calculator

Watts to Amps Calculator

Current depends on more than watts and volts. Pick your system type so the calculation uses the right relationship — power factor for AC, and √3 for three-phase.

Three-phase uses the line-to-line voltage, for example 400 V or 480 V.

Real power drawn by the load.

Ignored for DC. Roughly 1.0 for heaters, 0.8–0.95 for motors and many electronic loads.

Results update as you type. The calculator runs entirely in your browser — nothing you enter is sent anywhere.

Current83.33 A

Calculation breakdown

SystemDC
Real power1,000 W
Voltage12 V
Current (A) = Power (W) ÷ Voltage (V)
= 1,000 W ÷ 12 V
= 83.33 A

Before you rely on this

Current calculations are one input to circuit design, not a substitute for it. Conductor and protective-device sizing is governed by the wiring rules that apply in your jurisdiction and by the specific installation conditions. Have electrical work designed and verified by a qualified person.

Method

How the number is reached

For a DC circuit, current is simply power divided by voltage. AC is different: the voltage and current waveforms are not necessarily in step, so only part of the apparent power does useful work. Power factor is the ratio between them.

Three-phase adds another step. A balanced three-phase load spreads its power across three lines, and the line-to-line voltage is √3 times the line-to-neutral voltage, so the √3 appears in the denominator.

Applying P = V × I to an AC circuit without a power factor understates the current, which is exactly the direction that matters when you are sizing a cable or a breaker.

DC:            I = P ÷ V
Single phase:  I = P ÷ (V × PF)
Three phase:   I = P ÷ (√3 × V_LL × PF)
Apparent power: S (VA) = P (W) ÷ PF

Symbols

P
Real power in watts
V
Supply voltage in volts
V_LL
Line-to-line voltage of a three-phase supply
PF
Displacement power factor, between 0 and 1
I
Current in amps; line current for three-phase

Worked examples

The same maths, applied

Example

1,000 W inverter load on a 12 V battery

You want the DC current a 1,000 W load pulls from a 12 V battery, ignoring inverter losses.

I = 1,000 W ÷ 12 V
I = 83.33 A

Result: About 83 A before inverter losses. With a 90% efficient inverter the battery actually supplies closer to 93 A, which is why 12 V systems need very heavy cable at this power level.

Example

A 1,000 W motor on a 400 V three-phase supply

A balanced three-phase motor drawing 1,000 W of real power at a power factor of 0.85.

I = 1,000 W ÷ (1.732 × 400 V × 0.85)
I = 1,000 ÷ 588.9
I = 1.7 A

Result: About 1.7 A per line. The same 1,000 W on a 120 V single-phase supply at the same power factor would draw about 9.8 A.

Detail

DC reference table

For battery systems, the current at a given power falls as system voltage rises. This is the main practical argument for building larger systems at 24 V or 48 V.

DC current drawn at common battery-system voltages
Power12 V DC24 V DC48 V DC
100 W8.3 A4.2 A2.1 A
200 W16.7 A8.3 A4.2 A
500 W41.7 A20.8 A10.4 A
1,000 W83.3 A41.7 A20.8 A
2,000 W166.7 A83.3 A41.7 A

Currents are at the nominal voltage. Real DC current rises as battery voltage sags, so size conductors and fuses with margin.

Detail

AC reference table

Current drawn by a 1,000 W load on common AC supplies
SupplyPF 1.00PF 0.90PF 0.80
120 V single phase8.33 A9.26 A10.42 A
230 V single phase4.35 A4.83 A5.43 A
240 V single phase4.17 A4.63 A5.21 A
400 V three phase1.44 A1.6 A1.8 A
480 V three phase1.2 A1.34 A1.5 A

Three-phase rows use the line-to-line voltage and give the current in each line of a balanced load.

Detail

Choosing a power factor

  • Resistive loads — heaters, incandescent lamps, kettles — are close to 1.0.
  • Induction motors typically run between about 0.8 and 0.9 at full load, and much lower when lightly loaded.
  • Many switch-mode power supplies without power factor correction sit around 0.6–0.7.
  • If a nameplate quotes VA rather than W, that is apparent power: divide by voltage directly and leave power factor out of it.

Limits of the model

What it assumes, and where it stops

Assumptions

The power you enter is real power in watts, not apparent power in VA.

Three-phase loads are balanced across all three lines.

Voltage is the nominal supply voltage; three-phase figures are line-to-line.

Not covered

This is a steady-state calculation. Motors and compressors draw far more current while starting.

It does not size conductors, breakers or protective devices — those depend on installation method, ambient temperature, grouping, voltage drop and the wiring rules that apply where you are.

Distortion power factor from non-linear loads is not modelled; only displacement power factor is.

Sources

Where these figures come from

Next steps

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Last meaningful update: 2026-08-19. This date changes only when the model, the sources or the guidance change.