1 in to Mm – Answer with Formula

1 inch (in) equals 25.4 millimeters (mm).

The conversion from inches to millimeters is done by multiplying the inch value by 25.4, since 1 inch is defined exactly as 25.4 millimeters. This relationship comes from international agreement, making the conversion precise and consistent worldwide.

Conversion Tool

Conversion Formula

The formula to convert inches to millimeters is:

millimeters = inches × 25.4

This works because 1 inch is internationally agreed to be exactly 25.4 millimeters. When you multiply the inch value by 25.4, you convert the length into millimeters, which are smaller units.

Example: Convert 2 in to mm:

• Start with 2 inches
• Multiply by 25.4: 2 × 25.4 = 50.8
• The result is 50.8 millimeters

Conversion Example

• Convert 3.5 in to mm:
  • Take 3.5 inches
  • Multiply 3.5 by 25.4: 3.5 × 25.4 = 88.9
  • Result: 88.9 mm
• Convert 0.75 in to mm:
  • Start with 0.75 inches
  • Multiply 0.75 × 25.4 = 19.05
  • Result is 19.05 mm
• Convert 10 in to mm:
  • Take 10 inches
  • Multiply: 10 × 25.4 = 254
  • Result: 254 mm
• Convert 15.2 in to mm:
  • 15.2 inches multiplied by 25.4
  • Calculate: 15.2 × 25.4 = 386.08
  • Result is 386.08 mm

Conversion Chart

This chart shows inch values with their equivalent millimeter values by multiplying the inch number by 25.4. You can use it to quickly find conversions without doing calculations. Negative values represent lengths in the opposite direction or below a reference point.

Related Conversion Questions

• How many millimeters is exactly 1 inch?
• What is 1 in converted to mm with decimal precision?
• Can I convert 1 inch to millimeters without a calculator?
• Why does 1 inch equal 25.4 millimeters?
• How to quickly convert 1 in to mm in my head?
• Is 1 in always the same in millimeters worldwide?
• What tools can I use online to convert 1 inch to mm?

Conversion Definitions

In (inch): An inch is a unit of length in the imperial and US customary systems, equal to exactly 2.54 centimeters or 25.4 millimeters. It is commonly used in the United States, Canada, and the United Kingdom for measuring shorter distances, sizes, or heights.

Mm (millimeter): A millimeter is a unit of length in the metric system, equal to one thousandth of a meter. It is widely used internationally for precise measurements in science, engineering, and everyday applications where small distances are concerned.

Conversion FAQs

Is the inch to millimeter conversion exact or approximate?

The conversion from inches to millimeters is exact. By international agreement, 1 inch is defined as exactly 25.4 millimeters, so there is no approximation in the conversion factor, making measurements consistent worldwide.

How do I convert fractions of an inch to millimeters?

To convert fractions of an inch, first convert the fraction to a decimal number, then multiply by 25.4. For example, ½ inch is 0.5 in decimal, and 0.5 × 25.4 equals 12.7 mm.

Can I convert inches to millimeters without a calculator?

You can estimate by knowing that 1 inch is about 25 mm. For rough calculations, multiply the inch number by 25, then add a bit more for accuracy. But for precise results, using a calculator or tool is best.

Why do some sources give different values for inch to mm?

Differences usually come from rounding or old measurement standards. Since 1959, the inch is defined exactly as 25.4 mm, so any other value is less accurate or outdated.

Are inches and millimeters used in different industries?

Yes, inches are common in the US and UK for construction, manufacturing, and everyday measurements. Millimeters are preferred globally in science, engineering, and technical fields where metric units are standard.