A kilocalorie is 1,000 calories.
Kilocalories to Zettajoules Converter — kcal to ZJ
Convert Kilocalorie (kcal) to Zettajoule (ZJ) using the exact conversion factor (1 kilocalorie = 4.184e-18 zettajoule). See the formula, worked examples, and conversion table.
Kilocalories to Zettajoules converter
Converter
Energy Converter
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Context values
Some unit families need one extra value for a physically accurate result.
Zettajoule is 1e+21 joule units.
Result = input x 4184 / 1e+21.
Energy uses the joule as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Kilocalories to Zettajoules
Kilocalorie and Zettajoule both measure energy, and the conversion is especially useful for comparing nutrition labels (kilocalories) against scientific energy figures (joules). Specifically: A kilocalorie is 1,000 calories, and zettajoule is 1e+21 joule units.
Formula
zettajoules = kilocalories × 4.184e-18
This factor comes from each unit's defined relationship to the category's base unit: 1 kilocalorie equals 4184 base units, and 1 zettajoule equals 1e+21 base units, so dividing one by the other gives the direct kilocalorie-to-zettajoule factor of 4.184e-18.
Simple example
1 kcal × 4.184e-18 = 4.184e-18 ZJ
1 kilocalorie = 4.184e-18 zettajoules.
Real-world example
100 kcal × 4.184e-18 = 4.184e-16 ZJ
100 kilocalories = 4.184e-16 zettajoules.
Conversion table
| Kilocalorie (kcal) | Zettajoule (ZJ) |
|---|---|
| 1 kcal | 4.184e-18 ZJ |
| 10 kcal | 4.184e-17 ZJ |
| 100 kcal | 4.184e-16 ZJ |
| 500 kcal | 2.092e-15 ZJ |
| 1,000 kcal | 4.184e-15 ZJ |
| 2,000 kcal | 8.368e-15 ZJ |
Reverse conversion: Zettajoule to Kilocalorie
4.184e-18 ZJ × 2.390057e+17 = 1 kcal
4.184e-18 zettajoules = 1 kilocalorie.
kilocalories = zettajoules × 2.390057e+17
For a page dedicated to this direction, see Zettajoule to Kilocalorie.
Understanding the Kilocalorie (kcal)
A kilocalorie is 1,000 calories.
Understanding the Zettajoule (ZJ)
Zettajoule is 1e+21 joule units.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many zettajoules are in 1 kilocalorie?
1 kilocalorie equals 4.184e-18 zettajoules, using the exact defined conversion factor rather than an estimate.
How do I convert kilocalorie to zettajoule?
Multiply the kilocalorie value by 4.184e-18. The converter above does this instantly to whatever precision you set.
How do I convert zettajoule back to kilocalorie?
Use the reverse factor: 1 zettajoule equals 2.390057e+17 kilocalories. You can also use the swap control in the converter above to flip the direction instantly.
What is a kilocalorie?
Kilocalorie (kcal) is a unit of energy.
What is a zettajoule?
Zettajoule (ZJ) is a unit of energy.
Is the kilocalorie to zettajoule conversion exact?
Yes. Both kilocalorie and zettajoule are defined by fixed standards rather than physical artifacts, so the factor of 4.184e-18 used above is exact to as many digits as you choose to display.