Whether you’re working on a DIY project, reading blueprints, or involved in engineering or manufacturing, you’ll inevitably need to convert between millimeters (mm) and inches (in). Many fields require precise measurements in both metric and imperial units. Millimeters are part of the metric system, while inches are part of the US customary/imperial system.
This article provides a comprehensive guide to millimeter to inch conversions, including a handy conversion chart, formulas, and practical examples to make the process easier. Let’s dive in!
Understanding Millimeters and Inches
Before we dive into the conversion chart, it’s helpful to understand what millimeters and inches are.
What’s a millimeter?
A millimeter is a unit of length in the metric system. One millimeter is one-thousandth of a meter, and a meter is the standard unit of length in the International System of Units (SI).
To get a sense of how small a millimeter is, consider that a U.S. dime is about 1.35 mm thick.
What’s an inch?
An inch is a unit of length in the imperial and U.S. customary measurement systems. An inch is one-twelfth of a foot and one thirty-sixth of a yard. One inch is equal to 2.54 centimeters.
For a real-world example, think about a standard ruler, which is 12 inches long.
The Conversion Formula and Methods
So, how do you convert millimeters to inches? It’s pretty simple, actually.
The Basic Conversion Formula
To convert from millimeters to inches, you divide the number of millimeters by 25.4:
inches = millimeters ÷ 25.4
This is the most accurate conversion, and it will give you a decimal inch value.
Converting to Decimal Inches
Let’s say you want to convert 50mm to inches. You’d use the formula like this:
50 ÷ 25.4 = 1.9685 inches
Converting to Fractional Inches
Sometimes, you need a fractional inch value instead of a decimal. To do that, you multiply the decimal part by the denominator you want (like 16 for 1/16″).
For example, if the decimal is 0.5, multiplying by 2 would give you 1/2, multiplying by 4 would give you 2/4, and so on.
You can choose different levels of precision, like 1/16″, 1/32″, or even 1/64″, depending on what you need.
Millimeter to Inch Conversion Chart
Need to convert millimeters to inches quickly? This chart gives you both the approximate fractional inch equivalent and the exact decimal inch equivalent.
To use the chart, find the millimeter value you have, and then read across to find the matching inch value.
| Millimeters (mm) | Inches (Approximate Fractional) | Inches (Exact Decimal) |
|---|---|---|
| 1 mm | 1/25″ | 0.0394″ |
| 5 mm | 3/16″ | 0.1969″ |
| 10 mm | 3/8″ | 0.3937″ |
| 15 mm | 9/16″ | 0.5906″ |
| 20 mm | 13/16″ | 0.7874″ |
| 25 mm | 1″ | 0.9843″ |
| 50 mm | 2″ | 1.9685″ |
| 100 mm | 4″ | 3.9370″ |
| 150 mm | 5 7/8″ | 5.9055″ |
A note on rounding: Approximate fractional conversions are rounded to the nearest 1/8 inch. Decimal values are rounded to four decimal places.
How can I use a millimeter to inches conversion chart?
Converting between millimeters and inches comes in handy in a lot of situations, including:
- Woodworking
- Drafting
- Engineering
- Sewing
- Construction
- DIY projects around the house
For the best results:
- Use a ruler or tape measure to get the most accurate reading.
- Choose the level of precision that makes the most sense for what you’re doing.
Understanding both metric and imperial measurements is important, especially if you work in a field where both systems are used.
In Summary
Converting millimeters to inches is easy when you understand the formula, use a conversion chart, and remember a few handy tips.
In fields like engineering, manufacturing, and construction, accurate conversions are essential for correct dimensions and proper fit. A mistake could be costly.
Whether you use the conversion chart or the formula we’ve provided, you can get quick, accurate conversions every time.