Joules to Watt-hours Converter

How to convert Joules to Watt-hours

To convert Joules to Watt-hours, multiply the value in Joules by 0.00027777778. For example, 5 J = 0.0013888889 Wh.

If you need to convert from Joules to Watt-hours, the key figure to remember is that one Joules equals 0.00027777778 Watt-hours. This page gives you a live calculator, a full reference table, and the underlying formula so you can convert J to Wh with complete confidence.

Energy conversions appear in nutrition, fitness, physics, utility bills, and engineering. The same quantity of energy can be expressed in joules, calories, kilowatt-hours, or BTU depending on the context.

Understanding Joules and Watt-hours

The joule is the SI unit, but everyday contexts use others: food labels use kilocalories (often just called 'calories'), electricity bills use kilowatt-hours, and heating and cooling systems use BTU (British Thermal Units). One food calorie is actually a kilocalorie — 1,000 of the small physics calories — which is a frequent source of confusion.

How accurate is this conversion?

Energy conversions use standard definitions: 1 calorie = 4.184 joules, 1 kilowatt-hour = 3,600,000 joules, 1 BTU = 1,055.06 joules. These are internationally agreed values, making the conversions exact.

All conversion factors on ClearUnits are based on internationally recognised standards (the International System of Units, SI, and official definitions). Factors are reviewed for accuracy and the calculator uses full-precision values, rounding only the displayed result.

Quick reference: common Joules to Watt-hours values

The most frequently searched conversions are 1 Joules = 0.00027777778 Watt-hours, 5 Joules = 0.0013888889 Watt-hours, 10 Joules = 0.0027777778 Watt-hours, and 100 Joules = 0.027777778 Watt-hours. The full table further down covers every common value, and the calculator handles any number you need in between.