Gigajoules to Millijoules Converter
Enter the energy in gigajoules below to convert it to millijoules.
Convert Gigajoules to Millijoules
Enter a value in gigajoules (GJ) to convert to millijoules (mJ).
Gigajoule to Millijoule Conversion Table
Table showing various gigajoule measurements converted to millijoules. Click any preset value or arrow to load it into the converter.
| Gigajoules (GJ) | Millijoules (mJ) |
|---|---|
| 0.0000001 GJ | 100,000 mJ |
| 0.0000002 GJ | 200,000 mJ |
| 0.0000003 GJ | 300,000 mJ |
| 0.0000004 GJ | 400,000 mJ |
| 0.0000005 GJ | 500,000 mJ |
| 0.0000006 GJ | 600,000 mJ |
| 0.0000007 GJ | 700,000 mJ |
| 0.0000008 GJ | 800,000 mJ |
| 0.0000009 GJ | 900,000 mJ |
| 0.00000001 GJ | 10,000 mJ |
How to Convert Gigajoules to Millijoules
To convert gigajoules to millijoules, multiply the energy by the following conversion ratio: 1e+12 millijoules/gigajoule.
Since one gigajoule is equal to 1e+12 millijoules, you can use this simple formula to convert:
The energy in millijoules is equal to the energy in gigajoules multiplied by 1e+12.
For example, here's how to convert 5 gigajoules to millijoules using the formula above.
How Many Millijoules Are in a Gigajoule?
There are 1e+12 millijoules in a gigajoule, which is why we use this value in the formula above.
Our gigajoule to millijoule calculator automatically converts your energy measurements with full decimal and scientific precision across US customary, imperial, and SI metric standards.
Gigajoules and millijoules are both units used to measure energy. Keep reading to learn more about each unit.
What Is a Gigajoule?
A gigajoule is a unit of energy equal to 1,000,000,000 joules (J), the base unit for energy. Equal to 1,000,000,000 Joules, common in natural gas billing. [1]
The gigajoule is classified as an International System of Units (SI) unit of energy. Gigajoules can be abbreviated as GJ; for example, 1 gigajoule can be written as 1 GJ.
In the metric system, "giga" is the standard SI prefix for billions, or 10⁹. This makes the gigajoule (GJ) a convenient decimal multiple of the joule (J).
In practice, gigajoules (GJ) are widely used across large-scale industrial, bulk, and macro-level energy specifications 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 gigajoules (GJ) and millijoules (mJ), keep full floating-point precision (1 GJ = 1e+12 mJ; 1 mJ = 1e-12 GJ) during intermediate calculations and round only the final millijoule figure to match your instrument tolerance.
More Gigajoule & Millijoule Conversions
Need to calculate in the opposite direction? Use our millijoules to gigajoules calculator to switch your starting unit immediately. You can also explore related tools such as converting millijoules to gigajoules, converting joules to calories, or converting calories to joules.
Convert from Gigajoules
Frequently Asked Questions
References
- [1]NIST CODATA StandardNIST CODATA (CODATA Energy & Thermodynamic Constants)·Energy Metrology Standard — Gigajoules (GJ) to Millijoules (mJ)
- [2]NIST SP 811 SpecificationNIST SP 811 (NIST SP 811 App. B.9 (Energy, Work & Heat))·Unit Specifications: Gigajoule (GJ) & Millijoule (mJ)
- [3]BIPM ReferenceBIPM (Derived SI Unit: Joule (J))·Conversion Factors & Mathematical Basis (GJ to mJ)