Convert inches to mm

Length Converter with Inch (in) to Millimeter (mm) Conversion

Converting inches (in) to millimeters (mm) bridges US customary and metric measurements for engineering drawings, screen sizes, fasteners, and international shipping specs. By international agreement, one inch is exactly 25.4 millimeters, so mm = in × 25.4.

Inches to Millimeters Formula

mm = in × 25.4

Multiply the length in inches by 25.4 to get millimeters. This factor is exact under the 1959 international inch definition adopted for US customary and imperial units.

Common inch to millimeter values

Example: Bolt Length

A hardware spec lists a bolt length of 2.5 inches. What is that in millimeters?

• Identify the length in inches: 2.5 in
• Multiply by the conversion factor: 2.5 × 25.4
• Calculate the result: 63.5

2.5 inches equals exactly 63.5 mm.

About the Units

One Inch (in) equals 25.4 Millimeters (mm)

One Millimeter (mm) equals 0.03937 Inch (in)

Where This Conversion Is Used

• Convert Inch to Millimeter to ensure consistent values across calculations, reports, and measurement systems.
• Helps compare dimensions when switching between metric and imperial measurements, commonly required when reading construction drawings, machining tolerances, and US-based product specifications.
• Frequently used to validate dimensions taken from CAD models, blueprints, survey maps, and engineering documents that mix inch- and meter-based units.

Frequently Asked Questions

References

• NIST: Systems of Units of Measurement