Convert Calories to BTU
1 calorie (cal) equals 0.003965666831 British thermal units (BTU).
1 cal = 0.003965666831 BTU
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk calorie to BTU converter to paste a column from Excel.
How to Convert Calorie to BTU
- 1 cal = 0.003965666831 BTU
- 1 BTU = 252.1644007 cal
- Example: convert 15 cal to BTU: 15 cal = 15 × 0.003965666831 BTU = 0.05948500247 BTU
Reference conditions. cal: Thermochemical calorie, 4.184 J exactly. The International Table calorie is 4.1868 J. BTU: International Table BTU (BTU_IT), 1055.05585262 J exactly.
Formula
BTU = cal × 0.003965666831391
or BTU = cal ÷ 252.1644007218
Derivation from SI units:
- 1 cal (thermochemical) = 4.184 J (exact)
- 1 BTU_IT = 1055.05585262 J (exact)
- 1 cal = 4.184 J ÷ 1055.05585262 J per BTU = 0.003965666831391 BTU
Both units are defined exactly, so the factor is exact. Calorie definition: calorie; BTU definition: British thermal unit.
Worked examples
- A reading of 100 cal converts to 0.3965666831 BTU.
100 cal × 0.003965666831 = 0.3965666831 BTU - A value of 1000 cal is 3.965666831 BTU.
1000 cal × 0.003965666831 = 3.965666831 BTU
Calorie to BTU conversion table
| Calories (cal) | BTU |
|---|---|
| 1 cal | 0.003965666831 BTU |
| 10 cal | 0.03965666831 BTU |
| 100 cal | 0.3965666831 BTU |
| 250 cal | 0.9914167078 BTU |
| 500 cal | 1.982833416 BTU |
| 1000 cal | 3.965666831 BTU |
| 4184 cal | 16.59235002 BTU |
| 10000 cal | 39.65666831 BTU |
Where it's used
Calories are used for chemistry and calorimetry, while British thermal units appear in furnace, boiler and fuel ratings in the US. Both measure energy, work and heat, so the conversion is a fixed factor.
Calorie to other energy units
| Conversion | 1 cal equals |
|---|---|
| calorie to joule | 4.184 J |
| calorie to kilojoule | 0.004184 kJ |
| calorie to megajoule | 0.000004184 MJ |
| calorie to kilocalorie | 0.001 kcal |
| calorie to watt-hour | 0.001162222222 Wh |
| calorie to kilowatt-hour | 0.000001162222222 kWh |
| calorie to BTU | 0.003965666831 BTU |
| calorie to therm | 3.966613703 × 10⁻⁸ thm |
| calorie to electronvolt | 2.611447397 × 10¹⁹ eV |
| calorie to foot-pound | 3.085960033 ft·lbf |
| calorie to erg | 41840000 erg |
Frequently asked questions
How many British thermal units are in 1 calorie?
1 cal = 0.003965666831 BTU.
How do I convert calories to British thermal units?
Multiply the value in cal by 0.003965666831, or divide it by 252.1644007. For example, 15 cal × 0.003965666831 = 0.05948500247 BTU.
Is the cal to BTU conversion exact?
Yes. Both units are defined exactly, so the ratio is exact; its decimal form does not terminate and is shown here to 10 significant figures (more with the precision selector).
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "calorie (thermochemical) (cal_th)".
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "British thermal unit_IT (Btu_IT)".
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Convert Calories to BTU. Retrieved October 17, 2026, from https://scientificconverters.com/energy/calories-to-btu/
IEEE
Scientific Converters, "Convert Calories to BTU," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/energy/calories-to-btu/