Quick Answer: Calories to Joules
One calorie equals 4.184 joules (1 cal = 4.184 J).
Conversely, 1 J ≈ 0.239 cal.
Formula: J = cal × 4.184
Worked examples
- 1 cal = 4.184 J
- 5 cal = 20.92 J
- 10 cal = 41.84 J
Method and limitations
This page converts the small calorie (cal). The thermochemical calorie is defined as exactly 4.184 J, so J = cal × 4.184. A food-label Calorie (Cal, capital C) is a kilocalorie: 1 kcal = 1,000 cal = 4,184 J = 4.184 kJ. Calculations use full-precision constants; answers in this box are rounded for readability (≈ marks a rounded value) and the calculator shows up to 9 significant figures. cal here is the thermochemical small calorie (exactly 4.184 J). A food-label Calorie (Cal) is a kilocalorie (kcal) = 1,000 cal = 4,184 J.
Each factor is exact by definition, derived from exact definitions, or a documented conventional value — see the methodology and sources.
Conversion Formula
This page converts the small calorie (cal). The thermochemical calorie is defined as exactly 4.184 J, so J = cal × 4.184. A food-label Calorie (Cal, capital C) is a kilocalorie: 1 kcal = 1,000 cal = 4,184 J = 4.184 kJ.
cal, Cal, kcal and J
cal (small calorie) = 4.184 J. Cal or kcal (the food-label Calorie) = 1,000 cal = 4,184 J = 4.184 kJ. This calculator takes small calories; for a food-label value, multiply by 1,000 first or read the answer directly as kilojoules.
The conversion describes the same energy in a different unit. It does not say how the body uses that energy, and this page does not estimate exercise or dietary needs.
To move the result onto an electricity scale, use joules to kWh (1 kWh = 3,600,000 J).
Constants and their sources are listed on the methodology page.
Complete Guide to Calories to Joules Conversion
What is a calorie?
The small calorie (cal) is a non-SI unit of energy, historically the heat that raises one gram of water by one degree Celsius. The thermochemical calorie fixes it at exactly 4.184 J. The kilocalorie (kcal), written Calorie on food labels, is 1,000 of these.
What is a joule?
The joule (J) is the SI unit of energy: one newton acting over one metre, or one watt for one second. Kilojoules (kJ) are used on food labels; megajoules and kWh for fuels and electricity.
How the Conversion Works
Multiply calories by 4.184. Because the thermochemical calorie is defined in joules, the conversion is exact.
Why This Conversion Matters
The same word "calorie" names two units 1,000 times apart. Converting to joules with the unit stated removes that ambiguity.
Scientific Context
Several calorie definitions exist because the heat capacity of water varies with temperature. The SI recommends the joule for all energy quantities; NIST SP 811 lists both the thermochemical (4.184 J) and IT (4.1868 J) calories.
Step-by-Step Conversion Guide
Follow these steps to convert calories to joules manually:
Start with your value in calories
Example: You want to convert 10 cal
Apply the conversion formula
Use the formula: J = cal × 4.184
Calculate the result
10 cal = 41.84 J
Verify your answer
Use our calculator above to double-check your manual calculation.
Quick Mental Math Tip
Multiply by 4 and add about 4.6%: 100 cal → 400 + 18.4 = 418.4 J. For food kcal, the same digits give kilojoules: 250 kcal = 1,046 kJ.
Common Conversions
| Calories (cal) | Joules (J) | Joules → Calories |
|---|---|---|
| 1 cal | 4.184 | 1 J = 0.239006 cal |
| 5 cal | 20.92 | 5 J = 1.19503 cal |
| 10 cal | 41.84 | 10 J = 2.39006 cal |
| 50 cal | 209.2 | 50 J = 11.9503 cal |
| 100 cal | 418.4 | 100 J = 23.9006 cal |
| 500 cal | 2,092 | 500 J = 119.503 cal |
| 1000 cal | 4,184 | 1000 J = 239.006 cal |
| 10000 cal | 41,840 | 10000 J = 2,390.06 cal |
When You'll Need This Conversion
Chemistry and calorimetry
Convert reaction enthalpies and heat-capacity data published in cal or kcal into SI joules.
Reading food labels
Check that a kcal figure and a kJ figure on the same label describe the same energy.
Older technical literature
Bring calorie-based heat-transfer data into joule-based calculations.
Pro Tips for Accurate Conversions
Look at the capital letter
cal = small calorie; Cal or kcal = 1,000 cal. A factor-of-1,000 error is the most common mistake.
kcal → kJ uses the same 4.184
kJ = kcal × 4.184, so there is no need to go through small calories.
Common Mistakes to Avoid
Entering food Calories as calories
A 250 kcal snack entered as 250 cal gives 1,046 J instead of 1,046,000 J.
Multiply kcal by 1,000 first, or read the result as kJ.
Mixing calorie definitions
Thermochemical (4.184 J) and IT (4.1868 J) calories differ by about 0.07%.
Use the definition your source states.
Frequently Asked Questions
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Conversion factors on this page are either exact by definition, derived from exact definitions, or conventional values in documented use. Each is listed with its source in our conversion methodology and sources, which cites the BIPM SI Brochure, NIST Special Publication 811 and the relevant IEC or national standards. Results are rounded for display only; calculations use full precision.