Watt and Ampere Calculator
Battery System Tool

Battery Watts to Amps Calculator

Find the amp draw from a battery for any watt load. Enter load watts and battery voltage to get discharge current. Essential for sizing batteries, fuses, and wiring in off-grid, RV, marine, and UPS systems.

Conversion direction
Electrical system
Quick voltage presets
Calculated result1000 W · 120 V · DC
8.333 A
Formula usedI = P / V

Custom voltage is always supported.

Formulas Used

DCI = P / V

No power factor needed for DC circuits.

AC 1φI = P / (V × PF)

Single-phase AC — multiply voltage by power factor.

AC 3φI = P / (√3 × V × PF)

Three-phase AC — divide by √3 ≈ 1.732.

Frequently Asked Questions

How long will a 100Ah battery last running a 500W load at 12V?

500W / 12V = 41.67A draw. 100Ah / 41.67A = approximately 2.4 hours. Account for depth of discharge: a 50% DoD limit gives about 1.2 hours safely.

What size wire for 1000W at 12V?

1000W / 12V = 83.3A. For cable runs under 1 metre, use 25mm² (4 AWG) minimum. Always use appropriate fusing at the battery terminal.