Yes. By definition 1 inch equals exactly 25.4 mm.

How do I convert fractional inches?

Convert the fraction to decimal inches first (e.g., 3/8 = 0.375), then multiply by 25.4. You can use a separate fraction-to-decimal chart if needed.

Should I round to whole millimeters?

It depends on your tolerance. For fine machining, keep two or more decimals; for carpentry, whole millimeters are often sufficient.

unit calculator

Inches to Millimeters Converter

Convert US customary lengths to mm for manufacturing and woodworking.

Results

Millimeters: 63.50 mm

How to use this calculator

Enter the length in inches.
We multiply by 25.4 to convert to millimeters.
Copy the mm value for CAD drawings, CAM setups, or printer slicers.

Inputs explained

Inches: Length in inches. Decimals are supported for fine measurements; convert fractions (e.g., 3/8" = 0.375") before entering.

How it works

Multiply inches by exactly 25.4 to get millimeters.

Formula

mm = inches × 25.4

When to use it

Converting woodworking plans to metric tool settings.
Preparing 3D print models or CNC jobs that require millimeter units.
Ordering hardware from international suppliers who list sizes in millimeters.
Translating legacy imperial machine drawings into metric dimensions.
Checking clearances when metric-spec parts must fit in imperial-sized spaces.

Tips & cautions

Carry extra decimals if your machining tolerance is tight; round only at the final step.
For fractions (e.g., 3/8"), convert to decimal inches first (0.375) before entering.
Double-check small parts like screws where rounding can shift fit.
If your calipers only show inches, read the value and convert here instead of switching modes.
Standard plywood/board thicknesses (e.g., 3/4") can be converted once and reused across a project.
Keep a cheat sheet of common conversions (1/4", 1/2", 3/4") in mm near your tools.
Outputs decimal millimeters only—no fractional formatting.
Assumes positive lengths.
Rounding may differ from your machine’s precision settings.
Does not snap to standard metric sizes (e.g., M-thread diameters or nominal board sizes).
Does not account for kerf, tolerances, or fits—adjust your design for those separately.

Worked examples

2.5 inches

2.5 × 25.4 = 63.5 mm

0.75 inches

0.75 × 25.4 = 19.05 mm

1/4 inch (0.25 in)

0.25 × 25.4 = 6.35 mm

6 inches

6 × 25.4 = 152.4 mm

Deep dive

Convert inches to millimeters with the exact 25.4 factor for manufacturing, 3D printing, and woodworking.

Handles decimals and fractional conversions so you can move designs between imperial and metric workflows seamlessly.

Use this inches-to-mm converter when sourcing metric hardware for imperial projects.

Ideal for CNC, laser cutting, and 3D printing where millimeter units are standard.

FAQs

Is 25.4 exact?: Yes. By definition 1 inch equals exactly 25.4 mm.
How do I convert fractional inches?: Convert the fraction to decimal inches first (e.g., 3/8 = 0.375), then multiply by 25.4. You can use a separate fraction-to-decimal chart if needed.
Should I round to whole millimeters?: It depends on your tolerance. For fine machining, keep two or more decimals; for carpentry, whole millimeters are often sufficient.

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Round outputs to match your machining or carpentry tolerance. This converter does not account for kerf, fits, or material expansion; verify critical dimensions against your machine and drawing standards.