How to Convert Inches to Millimeters

Inches are common in many product and construction measurements, while millimeters are widely used for precise metric dimensions. Converting between them is straightforward.

Inches to MM Formula

Multiply inches by 25.4.

Millimeters = Inches × 25.4

Common Examples

• 1 inch = 25.4 mm
• 2 inches = 50.8 mm
• 5 inches = 127 mm
• 10 inches = 254 mm

Example

A measurement of 3.5 inches equals 88.9 millimeters because 3.5 × 25.4 = 88.9.

Practical Uses

This conversion is useful for hardware, pipe and tool sizes, technical drawings, screen dimensions, and product specifications.

Accuracy Tip

Because one inch equals exactly 25.4 millimeters, use the full factor before rounding the final result.

Converting Product Dimensions Correctly

Inches to millimeters is a common conversion when a product specification uses imperial units but the required drawing or measurement uses metric units. It is especially useful for small dimensions where a small rounding error can matter.

For example, a dimension of 0.5 inch becomes 12.7 mm exactly. Keeping that relationship in mind is useful when checking parts, tools, fasteners, and technical documentation.

Quick Conversion Reference

Inches	Millimeters
0.5	12.7
1	25.4
2	50.8
5	127
10	254

Frequently Asked Questions

What is the exact inches to mm factor?

Multiply inches by exactly 25.4.

Is 1/2 inch equal to 12.7 mm?

Yes, exactly.

Should I round millimeter results?

Only after the conversion. The appropriate rounding depends on the measurement's purpose.

Related Conversion Guides

• MM to Inches: Formula, Examples, and Conversion Guide
• CM to Inches: Formula, Examples, and Quick Conversion Guide

Useful for Tools and Technical Specifications

Inches-to-millimeters conversion is particularly useful when a specification uses fractions of an inch. For example, half an inch converts exactly to 12.7 mm, while a quarter inch converts to 6.35 mm. These familiar relationships can make quick checks easier. For more unusual decimal inch values, use the full 25.4 factor and round only after the calculation. This is preferable to using a rough mental factor when a part needs to fit another component.