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Convert Kilojoules to Kilocalories – Energy Converter

Quickly convert energy values from kilojoules (kJ) to kilocalories (kcal). This calculator is intended for everyday tasks—food labels, recipes, and basic lab bookkeeping—and uses SI-consistent definitions to avoid ambiguity.

In nutrition contexts the kilocalorie (kcal) is commonly shown as “Calorie” (capital C). In physics and engineering contexts the kilojoule (kJ) is the SI energy unit commonly used. This tool translates between them using the standard thermochemical definition.

Results are suitable for planning and record-keeping. For metrology-grade measurements (e.g., calorimetry research or regulated reporting) follow instrument calibration and uncertainty procedures described by national measurement authorities.

Updated Nov 28, 2025

Interactive Converter

Convert between kilojoule and kilocalorie with precision rounding.

Quick reference table

KilojouleKilocalorie
1 kJ4.18 kcal
5 kJ20.92 kcal
10 kJ41.84 kcal
25 kJ104.6 kcal
50 kJ209.2 kcal
100 kJ418.4 kcal

Methodology

The conversion is based on the internationally adopted thermochemical definition: 1 kilocalorie (1 kcal) = 4184 joules (J) = 4.184 kilojoules (kJ). This is the value used by national metrology bodies.

To convert kJ to kcal we apply the fixed mathematical relationship (divide kJ by 4.184). The calculator performs that operation and presents results with reasonable default rounding while preserving accuracy.

When using converted values for regulated reporting, lab records, or publication cite the originating measurement and report measurement uncertainty and calibration status according to guidance from national standards bodies.

Worked examples

100 kJ = 23.900 kcal (100 ÷ 4.184 = 23.900).

500 kJ = 119.501 kcal (500 ÷ 4.184 ≈ 119.501).

1000 kJ = 239.006 kcal (1000 ÷ 4.184 ≈ 239.006).

Further resources

Expert Q&A

What is the exact relationship between kJ and kcal?

By convention 1 kilocalorie (kcal) = 4184 joules (J) = 4.184 kilojoules (kJ). Use the factor 4.184 when converting between kJ and kcal.

Why do nutrition labels say “Calories” instead of kcal?

Food energy on nutrition labels commonly uses the term Calorie (capital C) to mean kilocalorie. Numerically, 1 Calorie (nutrition) = 1 kcal = 4.184 kJ. When converting labels, treat food Calories as kilocalories.

When should I worry about rounding or significant figures?

For recipes and daily tracking 1–2 decimal places are usually fine. For laboratory and metrology work, round to reflect instrument precision and include measurement uncertainty; avoid giving false precision beyond the instrument's calibrated uncertainty.

Can I use this calculator for calorimeter data or regulatory reporting?

This converter provides the mathematical conversion only. For calorimetry or regulated reporting pair converted values with instrument calibration certificates and uncertainty analysis following guidance from national measurement institutes before submission.

Are there different definitions of the calorie?

Historically several calorie definitions existed (thermochemical, international steam-table, etc.). The thermochemical definition (1 cal_th = 4.184 J) is the convention most commonly used for kcal ↔ kJ conversions today; consult national standards for context-specific definitions.

How do I account for measurement error when converting?

Convert the nominal value then propagate the measurement uncertainty. If your energy measurement has ±Δ kJ, convert both nominal and uncertainty by dividing by 4.184 to get kcal and ±Δ kcal. For formal uncertainty analysis follow guidance from metrology organizations.

Sources & citations