Joules to Watt Hours
An instant joules-to-watt hours converter, with the formula and a reference table below.
| Joules | Watt Hours |
|---|---|
| 1 J | 0.000278 Wh |
| 2 J | 0.000556 Wh |
| 3 J | 0.000833 Wh |
| 5 J | 0.001389 Wh |
| 10 J | 0.002778 Wh |
| 25 J | 0.006944 Wh |
| 50 J | 0.013889 Wh |
| 100 J | 0.027778 Wh |
How to use
- Enter a value in the Joules field.
- The Watt Hours figure appears immediately — no button to press.
- Typing in the Watt Hours field converts back to Joules the same way.
- Use the reference table for the values that come up most often.
Joules to Watt Hours formula
Converting joules to watt hours is a single multiplication by 0.000277777778.
Wh = J × 0.000277777778
Put another way, one joule is exactly 1/3,600 of a watt-hour.
Why this factor: the joule and the watt-hour are both defined against the joule, so dividing one definition by the other gives 0.000277777778 directly. Both definitions are set out in full below.
To go the other way, divide by 0.000277777778 — or use the Watt Hours to Joules converter, which is the same calculation reversed.
Worked example
Take 2000 J and multiply by the factor 0.000277777778: the result is 0.555556 Wh.
2000 J × 0.000277777778 = 0.555556 Wh
The converter above does this for any value you type, in either direction.
What is a joule?
The joule is the SI unit of energy — the work done by one newton acting over one meter.
Definition: Defined as 1 N·m, equivalently one watt-second. Named after James Prescott Joule.
Where it is used: All scientific energy calculations, food energy on European labels, and mechanical work.
What is a watt-hour?
A watt-hour is the energy delivered by one watt of power sustained for one hour.
Definition: Exactly 3,600 joules.
Where it is used: Battery capacity for laptops, e-bikes and power tools, and small-scale energy metering.
Worth knowing: Airline lithium-battery limits are set in watt-hours, which is why laptop and power-bank capacities are labelled in Wh.
Joules vs Watt Hours
The joule is an SI unit while the watt-hour is a specialized unit. That is why the factor between them is not a round number: the two systems were defined independently and only later tied together by exact agreement.
Frequently asked questions
How many watt hours are in a joule?
One joule equals 0.000277777778 watt hours.
What is the formula to convert joules to watt hours?
Multiply the number of joules by 0.000277777778. To reverse it, divide by 0.000277777778 instead.
How do I convert watt hours back to joules?
Divide by 0.000277777778, which is the same as multiplying by 3600.
How many watt hours are in 10 joules?
10 J works out to 0.002778 Wh.
Is there anything to watch out for with watt hours?
Airline lithium-battery limits are set in watt-hours, which is why laptop and power-bank capacities are labelled in Wh.
How is the joule defined?
Defined as 1 N·m, equivalently one watt-second. Named after James Prescott Joule.