Convert British Thermal Unit to Calorie (BTU → cal)
The British thermal unit is the standard for American HVAC systems, gas appliances, and air-conditioner ratings.
British Thermal Unit to Calorie Conversion Table
10 common values| British Thermal Unit | Calorie |
|---|---|
| 1 BTU | 252.1644 cal |
| 10 BTU | 2,521.644 cal |
| 100 BTU | 25,216.44 cal |
| 500 BTU | 126,082.2 cal |
| 1,000 BTU | 252,164.4 cal |
| 5,000 BTU | 1,260,822 cal |
| 10,000 BTU | 2,521,644 cal |
| 50,000 BTU | 12,608,220 cal |
| 100,000 BTU | 25,216,440 cal |
| 500,000 BTU | 126,082,200 cal |
How to Convert British Thermal Unit to Calorie Manually
Step by StepConverting BTU to calories is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.
- 1Take your value in BTUStart with the number of BTU (BTU) you want to convert.
- 2Multiply by 252.1644The conversion factor from BTU to cal is 252.1644. Multiply your value by this number.
- 3Read the result in caloriesThe result is your value in calories (cal).
Formula
Multiply the value in BTU by 252.1644. For the reverse direction, multiply by 0.003966.
cal = BTU × 252.1644BTU = cal × 0.003966Tips
Use these in everyday conversions- 1 BTU = 1055.06 J = 0.293 Wh.
- BTU/h (power) and BTU (energy) are different — don't confuse.
- Tons of refrigeration: 12,000 BTU/h = 1 ton AC.
Common Mistakes
Avoid these- Confusing BTU and BTU/h — energy vs power.
- Using kcal when BTU is requested in HVAC specs.
- Treating all BTUs as exact — definitions vary (IT, thermochemical, etc.).
About British Thermal Unit and Calorie
What is the British Thermal Unit?
The British thermal unit (BTU) equals approximately 1,055.06 joules and is the standard unit in American HVAC, gas appliances, and air-conditioner ratings. Originally defined as the heat needed to raise 1 pound of water by 1°F, the BTU is the imperial counterpart to the calorie. American gas utilities measure delivered heat in BTUs or therms (1 therm = 100,000 BTU), and air conditioners are rated by their cooling capacity in BTU per hour (a typical window AC is 5,000–12,000 BTU/h, central AC for a medium home is 24,000–60,000 BTU/h). Furnaces are similarly rated. The BTU relates to the joule (1 BTU ≈ 1,055 J), the calorie (1 BTU ≈ 252 cal), the watt-hour (1 BTU ≈ 0.293 Wh), and the therm (100,000 BTU = 1 therm). Outside the United States, the BTU is rare; metric countries use kilojoules or kilowatt-hours for the same applications.
- US air-conditioner sizing
- US heating-system capacity
- Natural gas billing in some US regions
Window AC: 5000–12,000 BTU/h. Central AC: 24,000–60,000 BTU/h. Home furnace: 60,000–100,000 BTU/h.
What is the Calorie?
The calorie equals exactly 4.184 joules (the 'thermochemical calorie') and is the historical unit for heat in chemistry and physics. It was originally defined as the heat needed to raise 1 gram of water by 1°C (a definition that varied slightly with starting temperature, hence multiple 'calories' — 4.184 J was set as the exact thermochemical convention). The calorie is widely used in older physics and chemistry literature for reaction energies, specific heat capacities, and thermodynamic calculations. Note: this 'small calorie' (lowercase c) is 1/1000 of the food Calorie (capital C) used in nutrition. The chemistry calorie relates to the joule (4.184 J = 1 cal), the kilocalorie (1,000 cal = 1 kcal = 1 food Calorie), and the BTU (1 BTU ≈ 252 cal). Modern SI usage in scientific publications has largely replaced the calorie with the joule, but it persists in medical and chemistry contexts.
- Thermodynamics and older physics texts
- Chemistry energy calculations
- Some engineering heat-transfer contexts
Raising 1 g of water 1 °C: 1 cal. A 100 kcal snack = 100,000 small calories.