British Thermal Units to Calories
Convert British thermal units to calories instantly — one British thermal unit is 252.164 calories.
| British Thermal Units | Calories |
|---|---|
| 1 BTU | 252.164401 cal |
| 2 BTU | 504.328801 cal |
| 3 BTU | 756.493202 cal |
| 5 BTU | 1260.822004 cal |
| 10 BTU | 2521.644007 cal |
| 25 BTU | 6304.110018 cal |
| 50 BTU | 12608.220036 cal |
| 100 BTU | 25216.440072 cal |
How to use
- Enter a value in the British Thermal Units field.
- The Calories figure appears immediately — no button to press.
- Typing in the Calories field converts back to British Thermal Units the same way.
- Use the reference table for the values that come up most often.
British Thermal Units to Calories formula
To convert British thermal units to calories, multiply by 252.164401.
cal = BTU × 252.164401
Why this factor: the British thermal unit and the calorie are both defined against the joule, so dividing one definition by the other gives 252.164401 directly. Both definitions are set out in full below.
To go the other way, divide by 252.164401 — or use the Calories to British Thermal Units converter, which is the same calculation reversed.
Worked example
Given 500 BTU, multiplying by 252.164401 yields 126082.200361 cal.
500 BTU × 252.164401 = 126082.200361 cal
The converter above does this for any value you type, in either direction.
What is a British thermal unit?
A BTU is the energy needed to raise one pound of water by one degree Fahrenheit.
Definition: The international-table BTU is about 1,055.056 joules.
Where it is used: US heating and air-conditioning capacity ratings, natural gas pricing, and boiler output.
Worth knowing: Air-conditioner ratings quoted as 'BTU' are really BTU per hour — a rate of cooling, not a quantity of energy.
What is a calorie?
A calorie is the energy needed to warm one gram of water by one degree Celsius.
Definition: The thermochemical calorie is defined as exactly 4.184 joules.
Where it is used: Chemistry and physics literature, and older engineering references.
Worth knowing: The 'calories' on a nutrition label are actually kilocalories — 1,000 of these. A 500-Calorie meal is 500 kcal, or about 2.1 million joules.
British Thermal Units vs Calories
The British thermal unit is a US customary unit while the calorie 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 calories are in a British thermal unit?
One British thermal unit equals 252.164401 calories.
What is the formula to convert British thermal units to calories?
Multiply the number of British thermal units by 252.164401. To reverse it, divide by 252.164401 instead.
How do I convert calories back to British thermal units?
Divide by 252.164401, which is the same as multiplying by 0.00396566683.
How many calories are in 10 British thermal units?
10 BTU works out to 2521.644007 cal.
Is there anything to watch out for with British thermal units?
Air-conditioner ratings quoted as 'BTU' are really BTU per hour — a rate of cooling, not a quantity of energy.
How is the British thermal unit defined?
The international-table BTU is about 1,055.056 joules.