Millimeters to Inches Calculator – MM to Inches Converter Online

  • Adam
  • November 22, 2025

Free millimeters to inches calculator. Convert mm to inches with decimal and fraction results. Includes inches to mm conversion, formulas, and conversion charts.

Millimeters to Inches Calculator

Convert MM to Inches & Inches to MM Instantly

MM ↔ Inches Converter

Understanding Millimeters to Inches Conversion

Millimeters and inches are both units of length, with millimeters being part of the metric system and inches part of the imperial system. The conversion between them is based on the international standard where 1 inch equals exactly 25.4 millimeters.

Conversion Formulas

MM to Inches:

Inches = mm / 25.4

or

Inches = mm × 0.0393701

Inches to MM:

mm = Inches × 25.4

Key Conversion Facts

  • 1 inch = 25.4 millimeters (exact international standard)
  • 1 millimeter = 0.0393701 inches (rounded to 7 decimals)
  • 10 mm ≈ 0.394 inches (approximately 25/64")
  • 25 mm ≈ 0.984 inches (approximately 63/64")
  • 100 mm = 3.937 inches (almost 4 inches)

Quick Reference Conversion Tables

MM to Inches

MM Inches (Decimal) Fraction
1 mm0.0394"~1/32"
5 mm0.1969"~13/64"
10 mm0.3937"~25/64"
15 mm0.5906"~19/32"
20 mm0.7874"~25/32"
25 mm0.9843"~63/64"
50 mm1.9685"~1 31/32"
100 mm3.9370"~3 15/16"

Inches to MM

Inches Millimeters
1/16"1.59 mm
1/8"3.18 mm
1/4"6.35 mm
1/2"12.70 mm
3/4"19.05 mm
1"25.40 mm
2"50.80 mm
5"127.00 mm

Frequently Asked Questions

How do you convert millimeters to inches?

To convert millimeters to inches, divide the millimeter value by 25.4. Formula: Inches = Millimeters / 25.4. Example: 100 mm = 100 / 25.4 = 3.937 inches. This is because 1 inch equals exactly 25.4 millimeters by international standard. You can also multiply millimeters by 0.0393701 to get the same result.

How many millimeters are in 1 inch?

1 inch equals exactly 25.4 millimeters. This is the international standard conversion factor established in 1959. Formula: mm = inches × 25.4. Example: 5 inches = 5 × 25.4 = 127 millimeters. This conversion is used worldwide for precise measurements in engineering, manufacturing, and construction.

What is 10mm in inches?

10 millimeters equals 0.3937 inches (or approximately 25/64 inch in fraction form). Calculation: 10 mm / 25.4 = 0.3937 inches. This is a common measurement for small hardware like bolts, jewelry sizing, and watch band widths. 10mm is just under 3/8 inch (0.375 inches).

How to convert mm to inches formula?

The mm to inches formula is: Inches = mm / 25.4 or Inches = mm × 0.0393701. Both formulas give the same result. The conversion factor 0.0393701 is equal to 1/25.4. For most calculations, dividing by 25.4 is simpler and more accurate. Example: 50 mm / 25.4 = 1.9685 inches.

What is 25mm in inches?

25 millimeters equals 0.9843 inches (approximately 63/64 inch or 15/16 inch). Calculation: 25 mm / 25.4 = 0.984252 inches. 25mm is slightly less than 1 inch and is commonly used in photography for lens focal length measurements, industrial bolts, and pipe fittings. It's the closest common metric size to 1 inch.

Disclaimer: This millimeters to inches calculator uses the international standard conversion factor: 1 inch = 25.4 millimeters (exact). Results are calculated to high precision. Fractional inch conversions are approximations rounded to the nearest specified fraction (1/8, 1/16, 1/32, or 1/64 inch). For critical engineering, manufacturing, or construction applications, always verify measurements with calibrated instruments and consult professional standards.

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