Zeptojoule is 1e-21 joule units.
Zeptojoules to Millijoules Converter — zJ to mJ
Convert Zeptojoule (zJ) to Millijoule (mJ) using the exact conversion factor (1 zeptojoule = 1e-18 millijoule). See the formula, worked examples, and conversion table.
Zeptojoules to Millijoules converter
Converter
Energy Converter
Convert joules, calories, kilowatt-hours, BTU, electronvolts, therms, and mechanical work units.
Context values
Some unit families need one extra value for a physically accurate result.
Millijoule is 0.001 joule units.
Result = input x 1e-21 / 0.001.
Energy uses the joule as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Zeptojoules to Millijoules
Zeptojoule and Millijoule both measure energy, and the conversion is especially useful for comparing nutrition labels (kilocalories) against scientific energy figures (joules). Specifically: Zeptojoule is 1e-21 joule units, and millijoule is 0.001 joule units.
Formula
millijoules = zeptojoules × 1e-18
This factor comes from each unit's defined relationship to the category's base unit: 1 zeptojoule equals 1e-21 base units, and 1 millijoule equals 0.001 base units, so dividing one by the other gives the direct zeptojoule-to-millijoule factor of 1e-18.
Simple example
1 zJ × 1e-18 = 1e-18 mJ
1 zeptojoule = 1e-18 millijoules.
Real-world example
100 zJ × 1e-18 = 1e-16 mJ
100 zeptojoules = 1e-16 millijoules.
Conversion table
| Zeptojoule (zJ) | Millijoule (mJ) |
|---|---|
| 1 zJ | 1e-18 mJ |
| 10 zJ | 1e-17 mJ |
| 100 zJ | 1e-16 mJ |
| 500 zJ | 5e-16 mJ |
| 1,000 zJ | 1e-15 mJ |
| 2,000 zJ | 2e-15 mJ |
Reverse conversion: Millijoule to Zeptojoule
1e-18 mJ × 1e+18 = 1 zJ
1e-18 millijoules = 1 zeptojoules.
zeptojoules = millijoules × 1e+18
For a page dedicated to this direction, see Millijoule to Zeptojoule.
Understanding the Zeptojoule (zJ)
Zeptojoule is 1e-21 joule units.
Understanding the Millijoule (mJ)
Millijoule is 0.001 joule units.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many millijoules are in 1 zeptojoule?
1 zeptojoule equals 1e-18 millijoules, using the exact defined conversion factor rather than an estimate.
How do I convert zeptojoule to millijoule?
Multiply the zeptojoule value by 1e-18. The converter above does this instantly to whatever precision you set.
How do I convert millijoule back to zeptojoule?
Use the reverse factor: 1 millijoule equals 1e+18 zeptojoules. You can also use the swap control in the converter above to flip the direction instantly.
What is a zeptojoule?
Zeptojoule (zJ) is a unit of energy.
What is a millijoule?
Millijoule (mJ) is a unit of energy.
Is the zeptojoule to millijoule conversion exact?
Yes. Both zeptojoule and millijoule are defined by fixed standards rather than physical artifacts, so the factor of 1e-18 used above is exact to as many digits as you choose to display.