Watts to Amps Calculator
Convert real power in watts to current in amps for DC/resistive loads, single-phase AC, or balanced three-phase AC. AC modes account for power factor, and the three-phase mode explicitly uses line-to-line voltage.
I=P/V · 1φ: I=P/(V×PF) · balanced 3φ: I=P/(√3×VLL×PF)How watts are converted to amps
DC / resistive AC
For DC, or an ideal resistive AC load at unity power factor, I = P ÷ V.
Single-phase AC
For real power P, RMS voltage V and power factor PF, I = P ÷ (V × PF).
Balanced three-phase AC
Using RMS line-to-line voltage VLL and line current, I = P ÷ (√3 × VLL × PF). This shortcut assumes a balanced three-phase load.
Apparent power
For the simplified AC model used here, apparent power is S = P ÷ PF in volt-amperes (VA). At PF=1, watts and VA have the same numeric value.
Watts to Amps Calculator Examples
The examples demonstrate the formulas only; they do not specify breaker or conductor sizes.
Resistive load
Single-phase AC
Balanced three-phase AC
Where a simple watts-to-amps conversion can fail
Power factor must match the load
The uploaded page suggested 0.8–0.9 as a general fallback. That can create false precision. For non-resistive AC loads, use reliable nameplate, datasheet, or measured information when the result matters.
Three-phase must be interpreted correctly
The √3 formula here uses line-to-line voltage and assumes a balanced three-phase system. Unbalanced systems require phase-specific analysis rather than this shortcut.
Motors need more than watts and PF
Motor nameplate current, efficiency, starting/inrush behavior, duty, and applicable motor-circuit rules can matter. A mechanical-output rating is not automatically the electrical input watts used by this formula.
Nominal current is not circuit sizing
A calculated load current does not by itself determine a safe breaker or wire size. The adopted electrical code and equipment instructions control the final design.
Inputs matter as much as the equation
The equations are straightforward, but the answer is only meaningful when the inputs describe the same electrical condition. For AC, watts should represent real input power, voltage should be the appropriate RMS voltage, and power factor should describe the load at the relevant operating point. For balanced three-phase mode, enter line-to-line voltage.
The calculator intentionally does not estimate power factor from appliance type and does not automatically apply a 125% “safety margin.” Code treatment depends on the load and installation. For example, NFPA materials define continuous-load concepts and include 125% provisions in applicable requirements, but that is not a universal instruction to multiply every calculator result by 1.25.