How do you convert millijoules to joules?

To convert millijoules (mJ) to joules (J), multiply the energy in millijoules by 0.001 (joules = millijoules × 0.001).

What is 5 millijoules in joules?

5 millijoules (5 mJ) is equal to 0.005 joules (0.005 J).

Which is larger, 1 millijoule (mJ) or 1 joule (J)?

One joule (J) is larger than one millijoule (mJ). Specifically, 1 J equals 1,000 mJ, while 1 mJ is 0.001 J.

How do I convert back from joules (J) to millijoules (mJ)?

To reverse the calculation from J to mJ, multiply your joule value by the inverse factor 1,000 (or divide by 0.001). You can also click the Swap button in the tool above to flip directions in one click.

How many decimal places should I round mJ to J results to?

For everyday comparisons and quick estimates, rounding to 2 decimal places is usually sufficient (for example, 5 mJ ≈ 0.01 J). For engineering, laboratory, or machining specifications, select 4 or 6 decimals—or Scientific (10ⁿ) mode—in the calculator toolbar above.

Millijoules to Joules Converter

Enter the energy in millijoules below to convert it to joules.

Joules to Millijoules (J → mJ)

Convert Millijoules to Joules

Enter a value in millijoules (mJ) to convert to joules (J).

Value (mJ)

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0.005joules

5 mJ = 0.005 J

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Suggested Conversions

Reference:NIST CODATA (CODATA Energy & Thermodynamic Constants)

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Millijoule to Joule Conversion Table

Table showing various millijoule measurements converted to joules. Click any preset value or arrow to load it into the converter.

Millijoules (mJ)	Joules (J)
1 mJ	0.001 J
2 mJ	0.002 J
2.5 mJ	0.0025 J
5 mJ	0.005 J
10 mJ	0.01 J
15 mJ	0.015 J
20 mJ	0.02 J
25 mJ	0.025 J
30 mJ	0.03 J
50 mJ	0.05 J

How to Convert Millijoules to Joules

To convert millijoules to joules, multiply the energy by the following conversion ratio: 0.001 joules/millijoule.

Since one millijoule is equal to 0.001 joules, you can use this simple formula to convert:

joules = millijoules × 0.001

The energy in joules is equal to the energy in millijoules multiplied by 0.001.

For example, here's how to convert 5 millijoules to joules using the formula above.

joules = (5 mJ × 0.001) = 0.005 J

How Many Joules Are in a Millijoule?

There are 0.001 joules in a millijoule, which is why we use this value in the formula above.

1 mJ = 0.001 J|1 J = 1,000 mJ

Our millijoule to joule calculator automatically converts your energy measurements with full decimal and scientific precision across US customary, imperial, and SI metric standards.

Millijoules and joules 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.

Learn more about millijoules in our Energy Converter.

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. [2]

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.

Learn more about joules in our Energy Converter.

When converting energy between millijoules (mJ) and joules (J), keep full floating-point precision (1 mJ = 0.001 J; 1 J = 1,000 mJ) during intermediate calculations and round only the final joule figure to match your instrument tolerance.

More Millijoule & Joule Conversions

Need to calculate in the opposite direction? Use our joules to millijoules calculator to switch your starting unit immediately. You can also explore related tools such as converting joules to millijoules, converting calories to joules, or converting kilojoules to joules.

Convert from Millijoules

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Frequently Asked Questions

There are 0.001 joules (J) in 1 millijoule (mJ). Conversely, 1 joule (J) is equal to 1,000 millijoules (mJ).

Energy Converter

Quick Info

Direct Factor: 1 millijoule (mJ) equals 0.001 joules (J).
Inverse Factor: 1 joule (J) equals 1,000 millijoules (mJ).
Formula: joules = millijoules ÷ 1000.
Verified Precision: Anchored to official NIST SP 811 and ISO/IEC 80000 standards.

Units Comparison

Millijoule (mJ)

One-thousandth of a Joule.

Joule (J)

Coherent SI unit of energy and work (1 W·s = 1 N·m).

Kilojoule (kJ)

Equal to 1,000 Joules.

References

[1]NIST CODATA · CODATA Energy & Thermodynamic Constants
Source
[2]NIST SP 811 · NIST SP 811 App. B.9 (Energy, Work & Heat)
Source
[3]BIPM · Derived SI Unit: Joule (J)
Source

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References

NIST · BIPM · ISO

[1]
NIST CODATA (CODATA Energy & Thermodynamic Constants)·Energy Metrology Standard — Millijoules (mJ) to Joules (J)
NIST CODATA Standard
[2]
NIST SP 811 (NIST SP 811 App. B.9 (Energy, Work & Heat))·Unit Specifications: Millijoule (mJ) & Joule (J)
NIST SP 811 Specification
[3]
BIPM (Derived SI Unit: Joule (J))·Conversion Factors & Mathematical Basis (mJ to J)
BIPM Reference

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