Electrical conversions · FREE TOOL

Watt-Hours Calculator

Calculate energy from watts and time, with minutes, hours and days, or find a battery’s nominal energy from Ah and voltage.

1

Your inputs

Edit the example
W
h

Example estimate · editable inputs

Energy used

800 Wh

In kilowatt-hours
0.8 kWh

Power is a rate in watts; energy is the accumulated amount in watt-hours.

BEHIND THE RESULT

How the calculation works

Wh = W × hours. Minutes ÷ 60 = hours. Days × 24 = hours. Nominal battery Wh = Ah × V.

Watts are the rate of using energy. Watt-hours are the total amount used. This tool calculates energy, not how long a battery will last.

A worked example

100 W for 8 hours is 800 Wh, or 0.8 kWh. The same energy results from 100 W for 480 minutes.

What this estimate can’t tell you

Assumes a known average power and duration. Nominal battery energy does not include usable capacity or conversion losses.

Sources & methodology

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