1 Inch to Millimeters

1 in = 25.4 mm

Calculation: mm = 1 in × 25.4 = 25.4 mm

Inch to Millimeter Converter

Choose the type of measurement to convert
Select the source unit to convert from
Select the target unit to convert to
Enter a numeric value or fraction to convert
Sig. Figures:

How long is 1 in?

1 in (2.54 cm) is comparable to the width of a thumb or the diameter of a coin.

What does 1 in look like?

Comparable to the width of a thumb or the diameter of a coin
1 in (2.54 cm) is comparable to the width of a thumb or the diameter of a coin.

1 in on the millimeter scale

in00.511.52mm01020304050

1 in = 25.4 mm

How to Convert Inch to Millimeter

1 inch = 25.4 millimeters exact

Millimeter = Inch × 25.4

Example: 1 in × 25.4 = 25.4 mm

Reverse Conversion

To convert millimeters back to inches:

  • Remember, 1 millimeter equals 0.0393701 inches.
  • To convert 25.4 mm to in, multiply 25.4 x 0.0393701, resulting in 1 in.

exact This conversion factor is exact by international definition.

1 in is also equal to:

About these units

Inch: Imperial/US customary unit standardized as exactly 25.4 millimeters since 1959.

Millimeter: Metric unit equal to one thousandth (1/1000) of a meter.

Frequently Asked Questions

How much is 1 inch in millimeters?

1 inch equals 25.4 millimeters. This is calculated by multiplying 1 by the conversion factor 25.4.

What does 1 inch look like in millimeters?

1 inch (25.4 millimeters) is about the width of a few fingers or a small smartphone.

How do you calculate 1 inch to millimeters?

Multiply 1 by the conversion factor 25.4. The calculation is 1 × 25.4 = 25.4 millimeters. This factor is defined by international measurement standards.

Share This Calculation

1 inch = 25.4 millimeters
1 inch = 25.4 millimeters — conversion chart

Nearby Conversions

2 inches50.8 millimeters 3 inches76.2 millimeters 4 inches101.6 millimeters 5 inches127 millimeters 6 inches152.4 millimeters 7 inches177.8 millimeters 8 inches203.2 millimeters 9 inches228.6 millimeters 10 inches254 millimeters 11 inches279.4 millimeters

For general conversions between inches and millimeters, see the inches to millimeters converter.

Also convert Inches to:

Conversion factors verified against NIST, BIPM, ISO 80000-3 1 inch = 2.54 cm by international agreement (1959). Last reviewed: March 2026
Adilson Fernandes By Adilson Fernandes
Tiago Fernandes Reviewed by Tiago Fernandes

All unit conversions on CoolConversion use conversion factors defined or documented by internationally recognised standards bodies (such as ISO and NIST), including both SI and non-SI units.