Electrical conversions · FREE TOOL

Amp-Hour Calculator

Calculate amp-hours from current and time, convert watt-hours of use to Ah, or find average watts from Ah, voltage and duration.

1

Your inputs

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A
h

Example estimate · editable inputs

Charge capacity

40 Ah

Nominal conversion only. No battery or inverter losses are included.

BEHIND THE RESULT

How the calculation works

Ah = A × h. From power: Ah = W × h ÷ V. Average W = Ah × V ÷ h.

Amp-hours describe charge. You need voltage to relate charge to energy, and duration to relate that energy to power.

A worked example

5 A for 8 hours is 40 Ah. A 60 W DC load over 8 hours at a nominal 12 V also uses 40 Ah. Conversely, 40 Ah at 12 V over 8 hours corresponds to 60 W on average.

What this estimate can’t tell you

These are nominal conversions with no battery, charger or inverter losses. Watts cannot be converted directly to Ah without voltage and time.

Sources & methodology

Formulas are derived from the units shown. Read our methodology or report a correction. Sources reviewed 2026-11-01.