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Millimeter Calculator

Convert millimeters to centimeters, meters, inches, feet, or mils and back.

Formula shown0 inputs definedUpdated Dec 2025By CalcuTotal TeamFree, no sign-up

Quick Summary

Use this when you need:

Convert technical drawings from mm into inches
Translate drill and fastener sizes between mm and inch specs
Switch between mm and cm for quick reporting

You’ll get:Length

How this is calculated

Formula:

in = mm / 25.4; cm = mm / 10

In plain language:

Millimeters convert to meters by dividing by 1000. Inches are defined by 1 in = 25.4 mm, so inches equal millimeters divided by 25.4.

The formula is always visible so you can verify the math and explain your numbers to anyone who asks.

What these terms mean

Length

Length used in the calculation.

When to use this calculator

Convert technical drawings from mm into inches
Translate drill and fastener sizes between mm and inch specs
Switch between mm and cm for quick reporting

Last updated: December 26, 2025

Millimeter calculator explained

Millimeters are common in machining, 3D printing, and technical drawings. Inches are common in US hardware and tool sizes. This calculator converts mm to inches and also shows nearby metric and inch-based reference units.

How the conversion works

The key exact definition is:

1\\,\\text{in} = 25.4\\,\\text{mm}

So:

\\text{in} = \\frac{\\text{mm}}{25.4}

And the reverse is:

\\text{mm} = 25.4 \\times \\text{in}

Units and conversions

Unit	Symbol	Relation
Millimeter	mm	$10^{-3}\\,\\text{m}$
Centimeter	cm	$10\\,\\text{mm} = 1\\,\\text{cm}$
Inch	in	$1\\,\\text{in} = 25.4\\,\\text{mm}$
Mil	mil	$1\\,\\text{mil} = 0.001\\,\\text{in}$

Worked examples

Converting 100 mm to inches
$\\text{in} = \\frac{100}{25.4} = 3.937008\\,\\text{in}$
Result: 3.937008 in.
Converting 1 inch to mm
$\\text{mm} = 25.4 \\times 1 = 25.4\\,\\text{mm}$
Result: 25.4 mm.

Tips and pitfalls

If you need fractions, convert mm to decimal inches first, then round to a fraction separately.
For tolerance stacks, keep more digits in inches during the math; round only when you publish the final dimension.
Mils are useful for thin materials; mm are useful for most mechanical parts.

References and further reading

Frequently Asked Questions

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Calculator info

Version:: v1.0.0
Last reviewed:: Dec 26, 2025
Sensitivity:: low
References:: 1

Last updated: December 26, 2025

Millimeter calculator explained

How the conversion works

The key exact definition is:

1\\,\\text{in} = 25.4\\,\\text{mm}

So:

\\text{in} = \\frac{\\text{mm}}{25.4}

And the reverse is:

\\text{mm} = 25.4 \\times \\text{in}

Units and conversions

Unit	Symbol	Relation
Millimeter	mm	$10^{-3}\\,\\text{m}$
Centimeter	cm	$10\\,\\text{mm} = 1\\,\\text{cm}$
Inch	in	$1\\,\\text{in} = 25.4\\,\\text{mm}$
Mil	mil	$1\\,\\text{mil} = 0.001\\,\\text{in}$

Worked examples

Converting 100 mm to inches
$\\text{in} = \\frac{100}{25.4} = 3.937008\\,\\text{in}$
Result: 3.937008 in.
Converting 1 inch to mm
$\\text{mm} = 25.4 \\times 1 = 25.4\\,\\text{mm}$
Result: 25.4 mm.

Tips and pitfalls

If you need fractions, convert mm to decimal inches first, then round to a fraction separately.
For tolerance stacks, keep more digits in inches during the math; round only when you publish the final dimension.
Mils are useful for thin materials; mm are useful for most mechanical parts.

Quick Summary

Calculator Tool

How this is calculated

What these terms mean

Length

When to use this calculator

Millimeter calculator explained

How the conversion works

Units and conversions

Worked examples

Tips and pitfalls

References and further reading

Frequently Asked Questions

Related Calculators

Metric Converter

Metric to Imperial Converter

Metric to Inches Calculator

Metric to SAE Calculator

Metric to Standard Converter

Mile Conversion Calculator

Was this calculator helpful?

Found an error?

Calculator info

Millimeter calculator explained

How the conversion works

Units and conversions

Worked examples

Tips and pitfalls

References and further reading

Frequently Asked Questions

Related Calculators

Metric Converter

Metric to Imperial Converter

Metric to Inches Calculator

Metric to SAE Calculator

Metric to Standard Converter

Mile Conversion Calculator

Was this calculator helpful?

Found an error?

Calculator info