Joules to Millijoules Converter
Enter the energy in joules below to convert it to millijoules.
Convert Joules to Millijoules
Enter a value in joules (J) to convert to millijoules (mJ).
Joule to Millijoule Conversion Table
Table showing various joule measurements converted to millijoules. Click any preset value or arrow to load it into the converter.
How to Convert Joules to Millijoules
To convert joules to millijoules, multiply the energy by the following conversion ratio: 1,000 millijoules/joule.
Since one joule is equal to 1,000 millijoules, you can use this simple formula to convert:
The energy in millijoules is equal to the energy in joules multiplied by 1,000.
For example, here's how to convert 5 joules to millijoules using the formula above.
How Many Millijoules Are in a Joule?
There are 1,000 millijoules in a joule, which is why we use this value in the formula above.
Our joule to millijoule calculator automatically converts your energy measurements with full decimal and scientific precision across US customary, imperial, and SI metric standards.
Joules and millijoules are both units used to measure energy. Keep reading to learn more about each unit.
What Is a Joule?
Coherent SI unit of energy and work (1 W·s = 1 N·m). It serves as a primary reference unit for measuring energy across scientific and practical applications. [1]
The joule is classified as an International System of Units (SI) unit of energy. Joules can be abbreviated as J; for example, 1 joule can be written as 1 J.
As the primary coherent reference unit for energy in this category, all other energy units are mathematically anchored to the joule (J).
In practice, joules (J) are widely used across standard energy applications within International System of Units (SI) workflows, engineering documentation, and technical data sheets.
What Is a Millijoule?
A millijoule is a unit of energy equal to 1/1,000 of a joule (0.001 J). One-thousandth of a Joule. [2]
The millijoule is classified as a metric and SI-compatible unit of energy. Millijoules can be abbreviated as mJ; for example, 1 millijoule can be written as 1 mJ.
In the metric system, "milli" is the standard SI prefix for thousandths, or 10⁻³. This makes the millijoule (mJ) a convenient decimal multiple of the joule (J).
In practice, millijoules (mJ) are widely used across fine-tolerance laboratory, analytical, and micro-scale energy measurements within SI metric workflows, engineering documentation, and technical data sheets.
When converting energy between joules (J) and millijoules (mJ), keep full floating-point precision (1 J = 1,000 mJ; 1 mJ = 0.001 J) during intermediate calculations and round only the final millijoule figure to match your instrument tolerance.
More Joule & Millijoule Conversions
Need to calculate in the opposite direction? Use our millijoules to joules calculator to switch your starting unit immediately. You can also explore related tools such as converting millijoules to joules, converting joules to calories, or converting joules to kilojoules.
Convert from Joules
Frequently Asked Questions
References
- [1]NIST CODATA StandardNIST CODATA (CODATA Energy & Thermodynamic Constants)·Energy Metrology Standard — Joules (J) to Millijoules (mJ)
- [2]NIST SP 811 SpecificationNIST SP 811 (NIST SP 811 App. B.9 (Energy, Work & Heat))·Unit Specifications: Joule (J) & Millijoule (mJ)
- [3]BIPM ReferenceBIPM (Derived SI Unit: Joule (J))·Conversion Factors & Mathematical Basis (J to mJ)