Convert Calories to British Thermal Units
Convert Calories (cal) to British Thermal Units (BTU) instantly and accurately.
Conversion Formula
BTU = cal × 0.003965666831
About Calories
A calorie (cal) - the thermochemical calorie - is exactly 4.184 J, defined as the heat to raise 1 g of water by 1°C. Standard since 1954. The calorie is the fundamental unit of heat measurement in thermochemistry: glucose combustion releases 669.9 kcal/mol; water vaporisation requires 539.7 cal/g. Bond dissociation energies in quantum chemistry are often quoted in kcal/mol. Note: the dietary Calorie (capital C) on food labels is 1 kcal = 4,184 J - a factor-of-1,000 difference that causes persistent confusion. 1 cal = 4.184 J = 1.163 × 10⁻³ Wh.
About British Thermal Units
A British Thermal Unit (BTU) - the heat to raise 1 lb of water by 1°F - equals exactly 1,055.05585262 J. It dominates US HVAC: room air conditioners are rated in BTU/h (5,000-24,000 BTU/h = 1.5-7.0 kW); one ton of refrigeration is exactly 12,000 BTU/h. Natural gas is billed in therms (100,000 BTU) in the US. Higher heating values: natural gas ~1,020-1,050 BTU/ft³; No. 2 fuel oil ~138,700 BTU/US gal; propane ~91,500 BTU/US gal. 1 BTU = 1,055.06 J = 252.164 cal = 0.29307 Wh.
Quick Reference Table
| Calories (cal) | British Thermal Units (BTU) |
|---|---|
| 1 cal | 0.00396567 BTU |
| 2 cal | 0.00793133 BTU |
| 5 cal | 0.0198283 BTU |
| 10 cal | 0.0396567 BTU |
| 25 cal | 0.0991417 BTU |
| 50 cal | 0.198283 BTU |
| 100 cal | 0.396567 BTU |