kcal to kJ Converter

Convert between kilocalories (kcal) and kilojoules (kJ) for food nutrition, diet planning, and fitness tracking.

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kcal to kJ Conversion:

1 Kilocalorie (kcal) = 4.184 Kilojoules (kJ)

kJ = kcal × 4.184 | kcal = kJ ÷ 4.184 (e.g., 100 kcal = 418.4 kJ)

kcal

Accepts decimals (e.g., 150.5 kcal = 629.692 kJ)

kJ

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Quick conversions (common food energy) - click to auto-fill:

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About kcal and kJ

Key differences between kilocalories (kcal) and kilojoules (kJ) — and their real-world uses

kcal vs kJ Comparison

Unit Definition 1 Unit = Common Uses
Kilocalorie (kcal) Energy to heat 1kg water by 1°C (food "calorie") 4.184 kJ
1000 small calories (cal)
US food labels, diet apps, fitness trackers
Kilojoule (kJ) Energy to move 1kg 1m with 1 newton force (SI unit) 0.239 kcal
1000 joules (J)
Global food labels (EU/Asia/AU), science, engineering

Kilocalorie (kcal)

  • Commonly called "calorie" on food labels (1 kcal = 1 food calorie)
  • Intuitive for daily use (e.g., average adult needs ~2000 kcal/day)
  • Primary unit in US, Canada, and most English-speaking countries
  • Used in MyFitnessPal, Weight Watchers, and fitness equipment

Kilojoule (kJ)

  • International System of Units (SI) for energy — global scientific standard
  • Required on food labels in 90% of countries (EU, Japan, Brazil, China)
  • 1 megajoule (MJ) = 1000 kJ (used for large energy values)
  • Directly convertible to other energy units (e.g., 1 kJ ≈ 0.278 watt-hours)

Common Food Energy (kcal & kJ)

Food Item (1 serving) Kilocalories (kcal) Kilojoules (kJ) Notes
Medium apple (~150g) 100 kcal 418.4 kJ Fresh, unpeeled
Cooked rice (~150g) 239 kcal 1000 kJ Long-grain, white
Hard-boiled egg (~50g) 78 kcal 326.35 kJ Medium-sized
Cheeseburger (fast-food) 500 kcal 2092 kJ With beef patty & cheese
Coca-Cola (330ml can) 139 kcal 581.6 kJ Regular (not diet)

kcal to kJ Conversion Table

Common energy conversions for food, diet, and fitness tracking

kcal → kJ

Kilocalories (kcal) = Kilojoules (kJ)
50 kcal = 209.2 kJ
100 kcal = 418.4 kJ
200 kcal = 836.8 kJ
500 kcal = 2092 kJ
1000 kcal = 4184 kJ

kJ → kcal

Kilojoules (kJ) = Kilocalories (kcal)
200 kJ = 47.8 kcal
500 kJ = 119.5 kcal
1000 kJ = 239.0 kcal
2000 kJ = 478.0 kcal
5000 kJ = 1195.0 kcal

Frequently Asked Questions

Common questions about kcal to kJ conversions

Why is the conversion factor exactly 4.184?

The 4.184 factor comes from the scientific definition of a kilocalorie:

  • 1 kcal is defined as the energy needed to heat 1 kilogram of water from 14.5°C to 15.5°C at standard atmospheric pressure.
  • Scientists measured this energy in joules (the SI unit of energy) and found it equals 4184 joules (J).
  • Since 1 kilojoule = 1000 joules, 4184 J = 4.184 kJ — hence 1 kcal = 4.184 kJ.
Is "Calorie" on food labels the same as kcal?

Yes! The "Calorie" (capital C) you see on food labels is actually a kilocalorie (kcal):

  • 1 food Calorie = 1 kcal = 1000 "small calories" (the scientific "cal" unit).
  • This naming shortcut started in the early 1900s to avoid confusing consumers with large numbers (e.g., "100 kcal" is easier than "100,000 cal").
  • To confirm: If a label says "Cal" or "Calories," it always refers to kcal.
How accurate do I need to be for diet tracking?

For most people, rounding to 1-2 decimal places is sufficient:

  • Everyday use: Round to 1 decimal place (e.g., 100 kcal ≈ 418.4 kJ → 418 kJ) — the difference won’t impact daily intake goals.
  • Precise tracking: Use 2 decimal places (e.g., 100 kcal = 418.40 kJ) — helpful for strict diets or bodybuilding.
  • Food labels: Manufacturers often round values to whole numbers (e.g., 418 kJ → 100 kcal) — you don’t need more precision than the label.
Why do some countries use kcal and others use kJ?

It depends on regional standards and historical adoption:

  • kcal users: US, Canada, UK (informally), and most English-speaking countries — legacy of early food labeling systems.
  • kJ users: EU, Australia, New Zealand, Japan, China, and most of Europe/Asia — adopted the SI unit (kJ) for global consistency.
  • Dual labeling: Many global brands now show both units to sell products in multiple markets (e.g., "100 kcal / 418 kJ").
Can I use this converter for exercise energy burn?

Yes — the conversion works for any energy measurement, including exercise burn:

  • Example 1: 30 minutes of jogging burns ~300 kcal → 300 × 4.184 = 1255.2 kJ.
  • Example 2: A treadmill shows 800 kJ burned → 800 ÷ 4.184 ≈ 191.2 kcal.
  • Note: Exercise energy estimates are approximate (vary by weight, intensity), but the conversion factor remains accurate.

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