Millijoule is 0.001 joule units.
Millijoules to Exajoules Converter — mJ to EJ
Convert Millijoule (mJ) to Exajoule (EJ) using the exact conversion factor (1 millijoule = 1e-21 exajoule). See the formula, worked examples, and conversion table.
Millijoules to Exajoules converter
Converter
Engineering Converter
Convert common stress, force, torque, power, and energy units used in engineering.
Context values
Some unit families need one extra value for a physically accurate result.
Exajoule is 1000000000000000000 joule units.
Result = input x 0.001 / 1e+18.
Energy units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Millijoules to Exajoules
Millijoule and Exajoule both measure a quantity used in structural or mechanical engineering — commonly stress, pressure, force, torque, power, or energy — where converting between the unit conventions used in different regions, industries, or equipment specifications is a routine part of design work. Specifically: Millijoule is 0.001 joule units, and exajoule is 1000000000000000000 joule units.
Formula
exajoules = millijoules × 1e-21
This factor comes from each unit's defined relationship to the category's base unit: 1 millijoule equals 0.001 base units, and 1 exajoule equals 1e+18 base units, so dividing one by the other gives the direct millijoule-to-exajoule factor of 1e-21.
Simple example
1 mJ × 1e-21 = 1e-21 EJ
1 millijoule = 1e-21 exajoules.
Real-world example
100 mJ × 1e-21 = 1e-19 EJ
100 millijoules = 1e-19 exajoules.
Conversion table
| Millijoule (mJ) | Exajoule (EJ) |
|---|---|
| 1 mJ | 1e-21 EJ |
| 10 mJ | 1e-20 EJ |
| 50 mJ | 5e-20 EJ |
| 100 mJ | 1e-19 EJ |
| 500 mJ | 5e-19 EJ |
| 1,000 mJ | 1e-18 EJ |
Reverse conversion: Exajoule to Millijoule
1e-21 EJ × 1e+21 = 1 mJ
1e-21 exajoules = 1 millijoules.
millijoules = exajoules × 1e+21
For a page dedicated to this direction, see Exajoule to Millijoule.
Understanding the Millijoule (mJ)
Millijoule is 0.001 joule units.
Understanding the Exajoule (EJ)
Exajoule is 1000000000000000000 joule units.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many exajoules are in 1 millijoule?
1 millijoule equals 1e-21 exajoules, using the exact defined conversion factor rather than an estimate.
How do I convert millijoule to exajoule?
Multiply the millijoule value by 1e-21. The converter above does this instantly to whatever precision you set.
How do I convert exajoule back to millijoule?
Use the reverse factor: 1 exajoule equals 1e+21 millijoules. You can also use the swap control in the converter above to flip the direction instantly.
What is a millijoule?
Millijoule (mJ) is a unit of engineering.
What is a exajoule?
Exajoule (EJ) is a unit of engineering.
Is the millijoule to exajoule conversion exact?
Yes. Both millijoule and exajoule are defined by fixed standards rather than physical artifacts, so the factor of 1e-21 used above is exact to as many digits as you choose to display.
Why do engineering unit conventions vary so much by region and industry?
Pressure, force, and stress can be expressed in metric (pascal, newton), US customary (psi, pound-force), or older and industry-specific units (atmosphere, torr, kip) depending on the country, industry, and even the equipment manufacturer, which is why engineers routinely need to convert between them when working across specs from different sources.