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Enter calories or BTU into the calculator to convert to the other value.
Assumptions Assumptions
- Conversions are energy-to-energy only using fixed definitions; no fuel-specific heating values or system losses are included.
- “Calorie” with a capital C (food Calorie) is treated as a kilocalorie (kcal) = 4184 J; the small “calorie” (cal) is 1/1000 of a kcal.
- Unit standards used: cal_th = 4.184 J; cal_IT = 4.1868 J; kcal = 4184 J; BTU (IT) = 1055.05585262 J; BTU (th) = 1054.35026444 J.
- Results are rounded to a sensible number of decimals for readability.
When to Use This Calculator
- Converting nutrition energy (Calories/kcal) to BTU for HVAC or engineering contexts.
- Standardizing between lab/engineering energy units (calorie variants) and BTU.
- Quick cross-checks when comparing heater specs, fuel charts, or energy budgets.
Input Definitions
- Calories — choose kilocalorie (kcal/Cal = 4184 J), thermochemical calorie (cal_th = 4.184 J), or International Table calorie (cal_IT = 4.1868 J).
- BTU — choose International Table (BTU_IT = 1055.05585262 J) or thermochemical (BTU_th = 1054.35026444 J).
- Conversions — General: Btu = cal × (J/cal) ÷ (J/Btu). Examples: 1 kcal ≈ 3.965667 BTU_IT; 1 BTU_IT ≈ 0.252164 kcal.
Cal to Btu Formula
The following formulas convert kilocalories (kcal/Cal) to BTU (International Table) and back; Joules are used as the bridge unit.
\mathrm{Btu_{IT}} = \mathrm{kcal} \times \frac{4184}{1055.05585262}\mathrm{kcal} = \frac{\mathrm{Btu_{IT}} \times 1055.05585262}{4184}- 1 kilocalorie (kcal, Cal) = 4184 J
- 1 thermochemical calorie (cal_th) = 4.184 J
- 1 international table calorie (cal_IT) = 4.1868 J
- 1 BTU (International Table) = 1055.05585262 J
- 1 BTU (thermochemical) = 1054.35026444 J
How do you convert calories to BTU? Pick the calorie type, convert to joules (multiply by J/cal), then divide by J/BTU; for kcal to BTU (IT), multiply kcal by 4184/1055.05585262 ≈ 3.965667.
How do you convert BTU to calories? Multiply BTU by its joule value, then divide by J/cal; for BTU (IT) to kcal, multiply by 1055.05585262/4184 ≈ 0.252164.
Cal to Btu Conversion Table
| Calories (kcal) | BTU (IT) |
|---|---|
| 0.25 | 0.991 |
| 0.50 | 1.983 |
| 1 | 3.966 |
| 1.5 | 5.949 |
| 2 | 7.931 |
| 2.5 | 9.914 |
| 3 | 11.897 |
| 4 | 15.863 |
| 5 | 19.828 |
| 7.5 | 29.743 |
| 10 | 39.657 |
| 12 | 47.588 |
| 15 | 59.485 |
| 20 | 79.313 |
| 25 | 99.142 |
| 30 | 118.970 |
| 40 | 158.627 |
| 50 | 198.283 |
| 75 | 297.425 |
| 100 | 396.567 |
| * With IT constants: 1 kcal ≈ 3.965667 BTU. | |
Example Problem
Convert 2.5 kcal (Cal) to BTU (IT).
Use the kcal formula: Btu_IT = kcal × 4184/1055.05585262.
Btu_IT = 2.5 × 4184/1055.05585262 ≈ 9.914 BTU
