Millijoules to Watt-hours Converter
Enter the energy in millijoules below to convert it to watt-hours.
Convert Millijoules to Watt-hours
Enter a value in millijoules (mJ) to convert to watt-hours (Wh).
Millijoule to Watt-hour Conversion Table
Table showing various millijoule measurements converted to watt-hours. Click any preset value or arrow to load it into the converter.
| Millijoules (mJ) | Watt-hours (Wh) |
|---|---|
| 1 mJ | 0.000000278 Wh |
| 10 mJ | 0.000002778 Wh |
| 100 mJ | 0.000027778 Wh |
| 1,000 mJ | 0.000277778 Wh |
| 10,000 mJ | 0.0027778 Wh |
| 100,000 mJ | 0.0277778 Wh |
| 1,000,000 mJ | 0.2777778 Wh |
| 5,000,000 mJ | 1.3888889 Wh |
| 10,000,000 mJ | 2.7777778 Wh |
| 25,400,000 mJ | 7.0555556 Wh |
How to Convert Millijoules to Watt-hours
To convert millijoules to watt-hours, multiply the energy by the following conversion ratio: 0.000000278 watt-hours/millijoule.
Since one millijoule is equal to 0.000000278 watt-hours, you can use this simple formula to convert:
The energy in watt-hours is equal to the energy in millijoules multiplied by 0.000000278.
For example, here's how to convert 5 millijoules to watt-hours using the formula above.
How Many Watt-hours Are in a Millijoule?
There are 0.000000278 watt-hours in a millijoule, which is why we use this value in the formula above.
Our millijoule to watt-hour calculator automatically converts your energy measurements with full decimal and scientific precision across US customary, imperial, and SI metric standards.
Millijoules and watt-hours are both units used to measure energy. Keep reading to learn more about each unit.
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. [1]
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.
What Is a Watt-hour?
A watt-hour is a unit of energy equal to 3,600 joules (J), the base unit for energy. Equal to 3,600 Joules. [2]
The watt-hour is classified as a metric and SI-compatible unit of energy. Watt-hours can be abbreviated as Wh; for example, 1 watt-hour can be written as 1 Wh.
When working with watt-hours (Wh) in formulas or technical specifications, always verify whether your target system uses SI metric, US customary, or British imperial standards.
In practice, watt-hours (Wh) are widely used across large-scale industrial, bulk, and macro-level energy specifications within SI metric workflows, engineering documentation, and technical data sheets.
When converting energy between millijoules (mJ) and watt-hours (Wh), keep full floating-point precision (1 mJ = 0.000000278 Wh; 1 Wh = 3,600,000 mJ) during intermediate calculations and round only the final watt-hour figure to match your instrument tolerance.
More Millijoule & Watt-hour Conversions
Need to calculate in the opposite direction? Use our watt-hours to millijoules calculator to switch your starting unit immediately. You can also explore related tools such as converting watt-hours to millijoules, converting ampere-hours to watt-hours, or converting milliampere-hours to watt-hours.
Convert from Millijoules
Frequently Asked Questions
References
- [1]NIST CODATA StandardNIST CODATA (CODATA Energy & Thermodynamic Constants)·Energy Metrology Standard — Millijoules (mJ) to Watt-hours (Wh)
- [2]NIST SP 811 SpecificationNIST SP 811 (NIST SP 811 App. B.9 (Energy, Work & Heat))·Unit Specifications: Millijoule (mJ) & Watt-hour (Wh)
- [3]BIPM ReferenceBIPM (Derived SI Unit: Joule (J))·Conversion Factors & Mathematical Basis (mJ to Wh)