Inches to Millimeters Converter

Inches (in)

⇄

Millimeters (mm)

Quick Conversions:

Conversion Formula

The conversion between inches and millimeters is based on the internationally accepted standard:

1 inch = 25.4 millimeters

To convert inches to millimeters, multiply the inch value by 25.4:

Millimeters = Inches × 25.4

To convert millimeters to inches, divide the millimeter value by 25.4:

Inches = Millimeters ÷ 25.4

Conversion Examples

Example 1: Convert 5 inches to millimeters

Start with the value: 5 inches
Apply the formula: 5 × 25.4 = 127
Result: 5 inches = 127 mm

Example 2: Convert 0.5 inches to millimeters

Start with the value: 0.5 inches
Apply the formula: 0.5 × 25.4 = 12.7
Result: 0.5 inches = 12.7 mm

Example 3: Convert 100 millimeters to inches

Start with the value: 100 millimeters
Apply the formula: 100 ÷ 25.4 = 3.937
Result: 100 mm = 3.937 inches

Inches to Millimeters Conversion Chart

Inches (in)	Millimeters (mm)
0.01	0.254
1/64 (0.0156)	0.397
1/32 (0.0313)	0.794
1/16 (0.0625)	1.588
1/8 (0.125)	3.175
1/4 (0.25)	6.35
1/2 (0.5)	12.7
1	25.4
2	50.8
3	76.2
4	101.6
5	127
6	152.4
7	177.8
8	203.2
9	228.6
10	254
12	304.8
15	381
20	508
24	609.6
30	762
36	914.4
48	1,219.2
50	1,270
60	1,524
72	1,828.8
100	2,540

Frequently Asked Questions

How many millimeters are in one inch?

One inch equals exactly 25.4 millimeters. This conversion factor was officially established in 1959 as part of the international yard and pound agreement, standardizing measurements across countries.

Why is the conversion factor 25.4?

The conversion factor of 25.4 was chosen to align the imperial inch with the metric system. Previously, various definitions of the inch existed, but in 1959, English-speaking nations agreed to define the inch as exactly 25.4 millimeters to create a unified standard.

How do I convert fractional inches to millimeters?

First, convert the fraction to a decimal. For example, 3/8 inch = 0.375 inch. Then multiply by 25.4: 0.375 × 25.4 = 9.525 mm. Common fractions like 1/2, 1/4, and 1/8 are frequently used in construction and manufacturing.

Which countries use inches versus millimeters?

The United States, Canada (alongside metric), and the United Kingdom primarily use inches for certain applications. Most other countries worldwide use the metric system with millimeters as the standard unit for small length measurements.

What is the precision needed for inch to mm conversions?

For most practical applications, rounding to one or two decimal places is sufficient. However, precision engineering, aerospace, and scientific applications may require three or more decimal places to maintain accuracy in measurements and manufacturing tolerances.

Can I use this converter for screen sizes?

Yes, but note that screen sizes measured in inches typically refer to the diagonal measurement of the display. To convert screen dimensions from inches to millimeters, apply the same conversion factor (multiply by 25.4) to each measurement.

How accurate are inch to millimeter conversions?

The conversion is mathematically exact using the factor 25.4. Any variations in accuracy come from rounding the result. Our converter maintains high precision and displays results with appropriate decimal places for your specific needs.

Popular Conversions

Fractional Inches	Decimal Inches	Millimeters
1/64″	0.0156″	0.397 mm
1/32″	0.0313″	0.794 mm
1/16″	0.0625″	1.588 mm
3/32″	0.0938″	2.381 mm
1/8″	0.125″	3.175 mm
5/32″	0.1563″	3.969 mm
3/16″	0.1875″	4.763 mm
1/4″	0.25″	6.35 mm
5/16″	0.3125″	7.938 mm
3/8″	0.375″	9.525 mm
7/16″	0.4375″	11.113 mm
1/2″	0.5″	12.7 mm
5/8″	0.625″	15.875 mm
3/4″	0.75″	19.05 mm
7/8″	0.875″	22.225 mm
1″	1″	25.4 mm

Related Length Conversions

About Inches and Millimeters

The Inch

The inch (symbol: in or ″) is a unit of length in the imperial and United States customary systems of measurement. Historically derived from the Latin “uncia” meaning one-twelfth, the inch has been defined in various ways throughout history. The modern inch was officially defined as exactly 25.4 millimeters in 1959 through an international agreement. The inch remains widely used in the United States for everyday measurements, construction, manufacturing, and screen sizes. There are 12 inches in a foot and 36 inches in a yard.

The Millimeter

The millimeter (symbol: mm) is a unit of length in the International System of Units (SI), representing one-thousandth of a meter. As part of the metric system, the millimeter offers easy scalability with other metric units through powers of ten. Millimeters are the standard for precision measurements in most countries worldwide, particularly in engineering, manufacturing, construction, and scientific applications. The metric system’s decimal-based structure makes conversions between units straightforward and reduces calculation errors.

Applications

Both units serve important roles in different contexts. Inches are commonly used for screen sizes, lumber dimensions, plumbing fixtures, and mechanical parts in countries using imperial measurements. Millimeters dominate in international manufacturing, precision engineering, automotive industries, and scientific research. Many industries now work with both systems, making accurate conversion between inches and millimeters essential for global commerce, product compatibility, and technical documentation.