How the calorie to BTU conversion works
Most confusion comes from two facts: (1) people say “calorie” but often mean kilocalorie (kcal, equal to food Calorie), and (2) there are slightly different BTU definitions. Here we use the widely accepted BTU (IT) = 1055.056 J, and the thermochemical calorie = 4.184 J, which is consistent with engineering sources like EngineeringToolbox.
Formulas
cal → J: \( J = \text{cal} \times 4.184 \)
kcal → J: \( J = \text{kcal} \times 4184 \)
BTU → J: \( J = \text{BTU} \times 1055.056 \)
Energy conversion: convert source → joule → target.
Power conversion: convert all to watt, using:
- 1 kcal/h = 4184 J / 3600 s = 1.163 W
- 1 BTU/h = 1055.056 J / 3600 s ≈ 0.293071 W
Why use this tool over generic unit converters
This page is tuned specifically to heat/energy contexts. It lets you work in the three most common domains at once: lab/physics (J, kJ), food/thermochemistry (cal, kcal), and HVAC/engineering (BTU, BTU/h, kcal/h, W). You don’t have to guess constants: they are embedded.
FAQ
1. What’s the difference between cal and kcal?
1 kcal = 1000 cal. Food labels use kcal but often write “Calorie” with a capital C.
2. Why are there different BTUs?
Yes, there are slightly different BTU definitions (IT, mean, thermochemical) differing within about 0.1%. We use the IT BTU, common in HVAC.
3. Can I use this for boiler sizing?
Yes, in the power tab you can convert kcal/h (common in European boilers) to BTU/h (common in US specs) or to kW.
Full original guide (expanded)
Below you can publish reference tables, normative sources, test cases, or notes for national standards. Keep this to outrank generic converters.
- Example: 500 kcal → BTU = 500 × 3.9683 ≈ 1984 BTU
- Example: 10,000 BTU/h → kW = 10,000 × 0.293071 / 1000 ≈ 2.93 kW
Formula (LaTeX) + variables + units
','\
cal → J: \( J = \text{cal} \times 4.184 \) kcal → J: \( J = \text{kcal} \times 4184 \) BTU → J: \( J = \text{BTU} \times 1055.056 \) Energy conversion: convert source → joule → target. Power conversion: convert all to watt, using: 1 kcal/h = 4184 J / 3600 s = 1.163 W 1 BTU/h = 1055.056 J / 3600 s ≈ 0.293071 W
- No variables provided in audit spec.
- CDC — Health topics — cdc.gov · Accessed 2026-01-19
https://www.cdc.gov/ - NIH — Health information — nih.gov · Accessed 2026-01-19
https://www.nih.gov/health-information - WHO — Health topics — who.int · Accessed 2026-01-19
https://www.who.int/health-topics
Last code update: 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.