Calories to British Thermal Units Converter
1 calorie ≈ 0.00396566683 British thermal units
This is the small calorie. The "Calorie" on food labels is a kilocalorie, which is 1,000 of these.
Several BTU definitions exist. This converter uses the International Table BTU, the one used by HVAC equipment ratings.
1 calorie equals 0.00396567 British thermal units
How to convert calories to British thermal units
Calories here are thermochemical (4.184 J), while BTU uses the International Table definition. A kilowatt-hour is energy (3.6 MJ), not power; a food Calorie is a kilocalorie.
BTU = cal × 0.003965666831One calorie is 0.003965666831 British thermal units, so a single multiplication converts any value.
0.0396567 BTU ≈ 10 × 0.003965666831This is the small calorie. The "Calorie" on food labels is a kilocalorie, which is 1,000 of these.
Several BTU definitions exist. This converter uses the International Table BTU, the one used by HVAC equipment ratings.
Calories to British thermal units conversion table
Common values in calories, converted to British thermal units.
| Calories (cal) | British thermal units (BTU) |
|---|---|
| 1 | 0.0039656668 |
| 2 | 0.0079313337 |
| 3 | 0.011897 |
| 4 | 0.015862667 |
| 5 | 0.019828334 |
| 10 | 0.039656668 |
| 20 | 0.079313337 |
| 25 | 0.099141671 |
| 50 | 0.19828334 |
| 100 | 0.39656668 |
| 250 | 0.99141671 |
| 500 | 1.9828334 |
| 1,000 | 3.9656668 |
About these units
caloriecal
The thermochemical calorie: exactly 4.184 joules.
Reference: NIST Special Publication 811.
British thermal unitBTU
The International Table BTU: 1,055.05585262 joules. The US heating and cooling unit.
Reference: NIST Special Publication 811.
Sources and precision
Table results are rounded to 8 significant digits; formula constants may be rounded to 10. Worked example answers use 6 significant digits. The converter starts at 6 significant digits and lets you change display precision. Calculations use the stored factors without intermediate rounding. Exact unit definitions do not make an input measurement more precise; conventional and measured factors follow the assumptions stated here.