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Millimeters to Inches Converter — CNC Machining Tolerances & 3D Printer Nozzles

Converting millimeters (mm) to decimal and fractional inches (in) is essential for CNC machinist toolmakers, aerospace fabricators, and 3D printing hobbyists translating metric hardware into US customary standards. In precision manufacturing, 1 inch equals exactly 25.4 millimeters (where 0.0254 mm equals one thousandth of an inch, or 1 "thou"). When setting a 0.4 mm 3D printer brass nozzle (0.0157 in) or inspecting an M8 bolt thread (0.315 in), dividing millimeters by 25.4 delivers pinpoint precision.

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Precision Millimeter Input Scale

mm
⇌
in
Everyday Micro Millimeter Objects:
Scale Visualizer
0 mm0.0 in
10 mm0.4 in
20 mm0.8 in
30 mm1.2 in
40 mm1.6 in
50 mm2.0 in
60 mm2.4 in
70 mm2.8 in
80 mm3.1 in
90 mm3.5 in
100 mm3.9 in
25.4 mm / 1 in
25.4 mm = 1 in
Roughly equivalent to the length/size of: 24.26 mm (US Quarter).

Measurement Breakdown

1 Inch = 25.4 Millimeters1 Millimeter = 0.03937008 Inches

Based on the international standard inch (exactly 25.4 mm).

Millimeters to Inches Precision Reference Table

Quick lookup chart for converting micro millimeters to decimal & fractional inches.

Millimeters (mm)Inches (in)Precision Hardware Benchmark
1 mm0.0394 in
5 mm0.1969 in
10 mm0.3937 in
25.4 mm1.0000 in
50 mm1.9685 in
100 mm3.9370 in

Converting in the reverse direction? Use our dedicated Inches to Millimeters Converter.

Overview & Capabilities

Converting millimeters (mm) to decimal and fractional inches (in) is essential for CNC machinist toolmakers, aerospace fabricators, and 3D printing hobbyists translating metric hardware into US customary standards. In precision manufacturing, 1 inch equals exactly 25.4 millimeters (where 0.0254 mm equals one thousandth of an inch, or 1 "thou"). When setting a 0.4 mm 3D printer brass nozzle (0.0157 in) or inspecting an M8 bolt thread (0.315 in), dividing millimeters by 25.4 delivers pinpoint precision.

Tutorial

How to Use

01
Enter the precision engineering dimension in Millimeters (mm).
02
The engine divides by 25.4 to compute decimal Inches (in) and closest 1/64" fraction.
03
Review machining presets (0.4 mm = 0.016 in, 3 mm = 0.118 in, 6.35 mm = 1/4 in, 12.7 mm = 1/2 in, 25.4 mm = 1.0 in).
04
Apply the decimal inch tolerances to your CNC lathe or G-code slicer program.
Capabilities

Key Features

CNC machining & 3D printer nozzle division engine (25.4 mm = 1 inch)
Machinist Presets: 0.40 mm (0.0157 in 3D nozzle), 3.0 mm (0.1181 in Bit), 6.35 mm (0.250 in 1/4" drill), 12.70 mm (0.500 in 1/2" shaft), 25.40 mm (1.000 in)
Closest fractional inch (1/16", 1/32", 1/64") conversion assistant
Instant responsive output
Applications

Common Use Cases

3D Slicer Configuration: Convert a 0.4 mm brass extruder nozzle diameter into 0.0157 inches for layer height extrusion.
CNC Milling Tolerance: Translate a 0.05 mm aerospace milling tolerance into 0.00197 inches (approx 2 thou).
Metric Hardware Replacement: Convert an M10 metric bolt thread diameter (10 mm) into 0.3937 inches.
Guidance

Tips & Best Practices

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Divide millimeters by 25.4 to get inches (e.g. 10 mm ÷ 25.4 = 0.3937 in).
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25.4 mm equals exactly 1.0 inch; 12.7 mm equals exactly 1/2 inch.
Ecosystem

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Answers

Frequently Asked Questions

Q How many inches is 25.4 mm?

25.4 millimeters equals exactly 1.0 inch.

Q What is a 0.4 mm 3D printer nozzle in inches?

0.4 mm equals approximately 0.01575 inches.

Q What is 10 mm in inches?

10 mm equals approximately 0.3937 inches (approx 25/64 inch).

Q What is 6 mm in inches?

6 mm equals approximately 0.2362 inches (approx 15/64 inch).