Convert Watt-hours to Kilojoules

About converting Watt-hours to Kilojoules

Watt-hours (Wh) and Kilojoules (kJ) are both units of energy, so converting between them is a single multiplication: multiply your Watt-hours figure by 3.6. Ten Watt-hours comes to 36 Kilojoules, and a hundred works out at 360 Kilojoules.

Rule of thumb: going from Watt-hours to Kilojoules multiplies, so the figure always grows — one Watt-hour is already 3.6 Kilojoules. If your answer came out smaller, you have the conversion the wrong way round.

What is a Watt-hour?

A watt-hour is energy, not power, and that distinction trips people up constantly. A watt is a rate — energy per second — so a watt-hour is what you get by sustaining that rate for an hour: a quantity of energy expressed as "this much power for this long". It is the natural unit for anything that stores energy and releases it gradually, which is why phone and laptop batteries are rated in watt-hours rather than the milliamp-hours stamped on the cell, and why airlines police lithium batteries by their watt-hour rating. Capacity in watt-hours tells you how long a load can run; watts alone never can.

What is a Kilojoule?

A kilojoule is a thousand joules, the size at which the joule becomes practical for everyday quantities. In Australia and New Zealand it is the primary unit on nutrition labels — food energy is quoted in kilojoules first, with calories relegated to a secondary figure or dropped entirely — so shoppers there think about daily intake in thousands of kilojoules rather than thousands of calories. It is also the working unit of chemistry, where reaction and bond energies are tabulated per mole. European labels print both kJ and kcal, which is why the same packet carries two different numbers for the same food.

To put both in perspective: a phone battery holds somewhere around 15 watt-hours, while a slice of bread carries roughly 300 kilojoules.

The converter above updates as you type, and the table lists common values for quick reference. Need the opposite direction? Use the Kilojoules to Watt-hours converter, or browse all Energy converters.