How do you convert kilojoules to millijoules?

To convert kilojoules (kJ) to millijoules (mJ), multiply the energy in kilojoules by 1,000,000 (millijoules = kilojoules × 1,000,000).

What is 5 kilojoules in millijoules?

5 kilojoules (5 kJ) is equal to 5,000,000 millijoules (5,000,000 mJ).

Which is larger, 1 kilojoule (kJ) or 1 millijoule (mJ)?

One kilojoule (kJ) is larger than one millijoule (mJ). Specifically, 1 kJ contains 1,000,000 mJ, whereas 1 mJ is 0.000001 kJ.

How do I convert back from millijoules (mJ) to kilojoules (kJ)?

To reverse the calculation from mJ to kJ, multiply your millijoule value by the inverse factor 0.000001 (or divide by 1,000,000). You can also click the Swap button in the tool above to flip directions in one click.

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

For everyday comparisons and quick estimates, rounding to 2 decimal places is usually sufficient (for example, 5 kJ ≈ 5,000,000.00 mJ). For engineering, laboratory, or machining specifications, select 4 or 6 decimals—or Scientific (10ⁿ) mode—in the calculator toolbar above.

Kilojoules to Millijoules Converter

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

Millijoules to Kilojoules (mJ → kJ)

Convert Kilojoules to Millijoules

Enter a value in kilojoules (kJ) to convert to millijoules (mJ).

Value (kJ)

From

Result

•

5,000,000millijoules

5 kJ = 5,000,000 mJ

Result updates automatically

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Suggested Conversions

Reference:NIST CODATA (CODATA Energy & Thermodynamic Constants)

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Kilojoule to Millijoule Conversion Table

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

Kilojoules (kJ)	Millijoules (mJ)
0.0000001 kJ	0.1 mJ
0.0000002 kJ	0.2 mJ
0.0000003 kJ	0.3 mJ
0.0000004 kJ	0.4 mJ
0.0000005 kJ	0.5 mJ
0.0000006 kJ	0.6 mJ
0.0000007 kJ	0.7 mJ
0.0000008 kJ	0.8 mJ
0.0000009 kJ	0.9 mJ
0.00000001 kJ	0.01 mJ

How to Convert Kilojoules to Millijoules

To convert kilojoules to millijoules, multiply the energy by the following conversion ratio: 1,000,000 millijoules/kilojoule.

Since one kilojoule is equal to 1,000,000 millijoules, you can use this simple formula to convert:

millijoules = kilojoules × 1,000,000

The energy in millijoules is equal to the energy in kilojoules multiplied by 1,000,000.

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

millijoules = (5 kJ × 1,000,000) = 5,000,000 mJ

How Many Millijoules Are in a Kilojoule?

There are 1,000,000 millijoules in a kilojoule, which is why we use this value in the formula above.

1 kJ = 1,000,000 mJ|1 mJ = 0.000001 kJ

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

Kilojoules and millijoules are both units used to measure energy. Keep reading to learn more about each unit.

What Is a Kilojoule?

A kilojoule is a unit of energy equal to 1,000 joules (J), the base unit for energy. Equal to 1,000 Joules. [1]

The kilojoule is classified as a metric and SI-compatible unit of energy. Kilojoules can be abbreviated as kJ; for example, 1 kilojoule can be written as 1 kJ.

In the metric system, "kilo" is the standard SI prefix for thousands, or 10³. This makes the kilojoule (kJ) a convenient decimal multiple of the joule (J).

In practice, kilojoules (kJ) are widely used across large-scale industrial, bulk, and macro-level energy specifications within SI metric workflows, engineering documentation, and technical data sheets.

Learn more about kilojoules in our Energy Converter.

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.

Learn more about millijoules in our Energy Converter.

When converting energy between kilojoules (kJ) and millijoules (mJ), keep full floating-point precision (1 kJ = 1,000,000 mJ; 1 mJ = 0.000001 kJ) during intermediate calculations and round only the final millijoule figure to match your instrument tolerance.

More Kilojoule & Millijoule Conversions

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

Convert from Kilojoules

Convert to Millijoules

Frequently Asked Questions

There are 1,000,000 millijoules (mJ) in 1 kilojoule (kJ). Conversely, 1 millijoule (mJ) is equal to 0.000001 kilojoules (kJ).

Energy Converter

Quick Info

Direct Factor: 1 kilojoule (kJ) equals 1,000,000 millijoules (mJ).
Inverse Factor: 1 millijoule (mJ) equals 0.000001 kilojoules (kJ).
Formula: millijoules = kilojoules × 1,000,000.
Verified Precision: Anchored to official NIST SP 811 and ISO/IEC 80000 standards.

Units Comparison

Kilojoule (kJ)

Equal to 1,000 Joules.

Millijoule (mJ)

One-thousandth of a Joule.

Joule (J)

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

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

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