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Guide

Watts to Amps Calculator

Watts to amps calculator: convert electrical power to current at any DC or nominal AC voltage. Size fuses, wire gauge, and battery discharge—free, instant.

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Power and voltage determine current. Whether you are checking a 12 V load, sizing an inverter feed, or verifying a breaker label, this guide explains the watts-to-amps relationship before you run the tool.

Benefits

  • Core DC formula: I (A) = P (W) ÷ V (V)—transparent and audit-friendly for field notes.
  • Works for 12 V, 24 V, 48 V buses and common nominal AC line voltages when power factor is ~1.
  • Pairs with wire-sizing and battery-runtime calculators once you know amp draw.

How it works

  1. Enter load power in watts (nameplate or measured).
  2. Enter system or circuit voltage in volts.
  3. Read current in amps; round up for fuse and conductor sizing per code practice.

FAQ

How do I convert watts to amps?

Divide watts by volts: Amps = Watts ÷ Volts. Example: 120 W on a 12 V circuit is 10 A. For AC with significant reactive load, use measured or power-factor-adjusted watts when available.

Does this work for AC and DC?

The same P ÷ V relationship applies when voltage is the value driving current in the circuit. For split-phase AC sizing, use the line-to-neutral or line-to-line voltage that matches how the load is wired.

Why do I need amps after watts?

Conductors, fuses, breakers, and BMS limits are rated in amps. Converting watts to amps at your bus voltage is the first step before NEC tables, inverter manuals, or battery C-rate checks.

Technical specifications

  • Formula: I (A) = P (W) ÷ V (V); assumes unity power factor unless noted.
  • Inputs: positive watts and volts.
  • Output: current (A) with calculation detail string.
  • Related: amps-to-watts, dc-cable-size, battery-runtime calculators.

Ohm's law and power

Power is voltage times current (P = V × I). Rearranging gives I = P ÷ V. For resistive DC loads this is exact; for motors and electronics, use average or nameplate watts at the voltage that supplies the load.

Sizing margin

Inrush and startup currents can exceed steady-state amps from a watts ÷ volts calculation. Use the result for continuous rating; consult equipment manuals for peak amps before selecting breakers or battery discharge limits.