Convert BTU to Joules
BTU to joules is the conversion you need when a heating, cooling, or appliance rating is given in British thermal units but you want the answer in the metric energy unit. One BTU is exactly 1055.05585262 joules, so the joule number always comes out much larger.
British thermal units to Joules conversion table
| British thermal units (BTU) | Joules (J) |
|---|---|
| 1 | 1,055.055853 |
| 2 | 2,110.111705 |
| 3 | 3,165.167558 |
| 5 | 5,275.279263 |
| 10 | 10,550.558526 |
| 20 | 21,101.117052 |
| 50 | 52,752.792631 |
| 100 | 105,505.585262 |
| 500 | 527,527.92631 |
| 1,000 | 1,055,055.85262 |
The formula
To convert BTU to joules, multiply the number of BTU by 1055.05585262:
joules = BTU × 1055.05585262
A worked example
Say you have 1000 BTU and want it in joules:
1000 × 1055.05585262 = 1,055,055.85 J
So 1000 BTU is about 1,055,056 joules — a little over a megajoule.
Why the number is exact
The International Table BTU is defined as exactly 1055.05585262 joules, so the factor isn't measured or rounded — it's fixed by definition. One thing to keep in mind: the "BTU" (British thermal unit) here is the International Table BTU. Other BTU definitions (thermochemical, 39°F, 60°F) differ slightly — by roughly 0.1% — so a value pulled from another source may be a touch different from what this page gives.
When you'll use it
Reading the energy rating on a heater, furnace, or air conditioner and putting it into joules, comparing appliance specs across metric and imperial sources, or working through a physics or engineering problem that mixes the two unit systems.
Frequently asked questions
How many joules are in a BTU?
Exactly 1055.05585262 joules. This uses the International Table BTU, the definition most engineering references and appliance specs are built on.
Why do I sometimes see a slightly different number of joules per BTU?
Because there is more than one BTU. This page uses the International Table BTU (1055.05585262 J). Other definitions — thermochemical, 39°F, 60°F — differ by roughly 0.1%, so a value from another source may be a touch different.
Is the BTU to joules conversion exact?
Yes, for the International Table BTU. It is defined as exactly 1055.05585262 joules, with nothing rounded away — though a different BTU definition would give a slightly different figure.