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Energy
Calories to BTU
Convert calories (cal) to BTU (BTU). Type a value below to see the result update instantly. Reference table and formula included.
Calculator
1 cal = 0.003966 BTU
Calories to BTU Conversion Table
Common values, ready to copy:
| calories | BTU |
|---|---|
| 1 cal | 0.003966 BTU |
| 2 cal | 0.007931 BTU |
| 5 cal | 0.019828 BTU |
| 10 cal | 0.039657 BTU |
| 25 cal | 0.099141 BTU |
| 50 cal | 0.198283 BTU |
| 100 cal | 0.396565 BTU |
| 1,000 cal | 3.9657 BTU |
Formula
BTU = calories × 3.96565124e-3
Energy uses the SI joule. Food calories (kcal) are 1,000 small calories: 1 kcal = 4,184 J. 1 kWh = 3.6 MJ = 3,600,000 J. 1 BTU = 1,055.06 J.
About Calories and BTU
Calories (cal): Originally defined as the energy to raise one gram of water by one degree Celsius; exactly 4.184 J in the modern definition (the thermochemical calorie). Common uses: Scientific work in chemistry, where the small calorie is the natural unit for heat-of-reaction measurements.
BTU (BTU): British Thermal Unit; the energy to raise one pound of water by one degree Fahrenheit; defined as exactly 1,055.06 J. Common uses: US heating and air conditioning (a 24,000 BTU air conditioner cools roughly a 1,500 sq ft room), and US natural gas billing.
How the conversion works
Energy uses the SI joule. Food calories (kcal) are 1,000 small calories: 1 kcal = 4,184 J. 1 kWh = 3.6 MJ = 3,600,000 J. 1 BTU = 1,055.06 J.
The exact relationship is BTU = calories × 3.96565124e-3, which the calculator at the top of this page applies in both directions. Type into either field and the other updates immediately.
When this conversion matters
Converting between calories and BTU comes up wherever energy measurements move between systems — from one country's conventions to another's, from a scientific reference to a practical specification, or from one industry's working unit to another's. The calculator and reference table above cover the everyday range; for unusual values you can type any number into either field.