A gigajoule (GJ) is a metric-prefixed unit of energy equal to 109 joules, using the SI giga prefix.
Gigajoules to Millijoules
Convert Gigajoule (GJ) to Millijoule (mJ) instantly with an exact formula, conversion table, and FAQ.
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Convert gigajoules (GJ) to millijoules (mJ) instantly with formula, conversion table, and FAQ.
Context values
Some unit families need one extra value for a physically accurate result.
A millijoule (mJ) is a metric-prefixed unit of energy equal to 10-3 joules, a fraction of a single joule, using the SI milli prefix.
mJ = GJ × 1000000000000
Results update instantly for Gigajoules to Millijoules conversions.
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Formula
mJ = GJ × 1000000000000
GJ = mJ × 1.000000000e-12
Conversion table
| 1 GJ | 1.000000e+12 mJ |
| 5 GJ | 5.000000e+12 mJ |
| 10 GJ | 1.000000e+13 mJ |
| 20 GJ | 2.000000e+13 mJ |
| 50 GJ | 5.000000e+13 mJ |
| 100 GJ | 1.000000e+14 mJ |
| 500 GJ | 5.000000e+14 mJ |
| 1000 GJ | 1.000000e+15 mJ |
Related conversions
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How the formula works
Both gigajoule and millijoule measure the same physical quantity, so converting between them is a single multiplication. Multiply a value in gigajoules by 1000000000000 to get millijoules. To reverse the conversion, multiply a millijoule value by 1.000000000e-12 to get back to gigajoules.
Frequently asked questions
What is Gigajoule (GJ)?
A gigajoule (GJ) is a metric-prefixed unit of energy equal to 109 joules, using the SI giga prefix.
What is Millijoule (mJ)?
A millijoule (mJ) is a metric-prefixed unit of energy equal to 10-3 joules, a fraction of a single joule, using the SI milli prefix.
How do I convert gigajoules to millijoules?
Multiply the gigajoule value by 1000000000000 to get the equivalent in millijoules. For example, 5 GJ × 1000000000000 = 5.000000e+12 mJ.
Is this conversion exact?
Yes. Both units are defined against the SI base unit for this dimension, so the factor 1000000000000 is an exact, non-rounded value.
Can I convert millijoules back to gigajoules?
Yes. Divide the millijoule value by 1000000000000, or multiply it by 1.000000000e-12, to get gigajoules.
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About converting gigajoules to millijoules
A gigajoule (GJ) is a metric-prefixed unit of energy equal to 109 joules, using the SI giga prefix. A millijoule (mJ) is a metric-prefixed unit of energy equal to 10-3 joules, a fraction of a single joule, using the SI milli prefix.
Use this calculator to move between gigajoules and millijoules accurately for homework, engineering, billing, or everyday energy calculations. The Universal Converter uses exact unit factors, so results stay consistent across the site.