Yoctojoule is 1e-24 joule units.
Yoctojoules to Millijoules Converter — yJ to mJ
Convert Yoctojoule (yJ) to Millijoule (mJ) using the exact conversion factor (1 yoctojoule = 1e-21 millijoule). See the formula, worked examples, and conversion table.
Yoctojoules to Millijoules 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.
Millijoule is 0.001 joule units.
Result = input x 1e-24 / 0.001.
Energy units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Yoctojoules to Millijoules
Yoctojoule and Millijoule 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: Yoctojoule is 1e-24 joule units, and millijoule is 0.001 joule units.
Formula
millijoules = yoctojoules × 1e-21
This factor comes from each unit's defined relationship to the category's base unit: 1 yoctojoule equals 1e-24 base units, and 1 millijoule equals 0.001 base units, so dividing one by the other gives the direct yoctojoule-to-millijoule factor of 1e-21.
Simple example
1 yJ × 1e-21 = 1e-21 mJ
1 yoctojoule = 1e-21 millijoules.
Real-world example
100 yJ × 1e-21 = 1e-19 mJ
100 yoctojoules = 1e-19 millijoules.
Conversion table
| Yoctojoule (yJ) | Millijoule (mJ) |
|---|---|
| 1 yJ | 1e-21 mJ |
| 10 yJ | 1e-20 mJ |
| 50 yJ | 5e-20 mJ |
| 100 yJ | 1e-19 mJ |
| 500 yJ | 5e-19 mJ |
| 1,000 yJ | 1e-18 mJ |
Reverse conversion: Millijoule to Yoctojoule
1e-21 mJ × 1e+21 = 1 yJ
1e-21 millijoules = 1 yoctojoule.
yoctojoules = millijoules × 1e+21
For a page dedicated to this direction, see Millijoule to Yoctojoule.
Understanding the Yoctojoule (yJ)
Yoctojoule is 1e-24 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 yoctojoule?
1 yoctojoule equals 1e-21 millijoules, using the exact defined conversion factor rather than an estimate.
How do I convert yoctojoule to millijoule?
Multiply the yoctojoule value by 1e-21. The converter above does this instantly to whatever precision you set.
How do I convert millijoule back to yoctojoule?
Use the reverse factor: 1 millijoule equals 1e+21 yoctojoules. You can also use the swap control in the converter above to flip the direction instantly.
What is a yoctojoule?
Yoctojoule (yJ) is a unit of engineering.
What is a millijoule?
Millijoule (mJ) is a unit of engineering.
Is the yoctojoule to millijoule conversion exact?
Yes. Both yoctojoule and millijoule 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.