Inches to millimeters (fractions)
Type in inches (like 3/8, 1 1/4 or 0.75) or in millimeters. The chart shows the fractions most used for tools, pipes and bolts.
How to useInches to mm and mm to inches
Available in: 
Inches to millimeters (fractions): what it is for
The converter accepts inches as a fraction (3/8), mixed number (1 1/4) or decimal (0.375) and shows the value in millimeters, centimeters and decimal inches. The other way, it turns millimeters into inches and shows the closest 1/64 fraction, with the difference in millimeters.
The chart lists the most common fractions, from 1/64" to 4", with your size highlighted.
How to use
- Type the size in inches or millimeters.
- See the conversion and the closest fraction.
- Check the chart of common fractions.
When to use it
- Choosing an inch wrench or drill bit.
- Buying bolts and imported tools.
- Converting sizes in projects and technical drawings.
Frequently asked questions
How many millimeters are in an inch?
Exactly 25.4 mm. To convert, multiply inches by 25.4; to go back, divide millimeters by 25.4.
How do I type fractions?
Use a slash: 1/4, 3/8, 5/16. For a mixed number, leave a space: 1 1/4 is one and a quarter inches. Decimals work too, like 0.375.
Why isn't a 1/2" wrench the same as a 1/2" pipe?
Wrenches, drill bits and bolts use the actual size in inches. Pipes and plumbing threads (NPT/BSP) use a nominal size: a 1/2" pipe has an outside diameter of about 21 mm, not 12.7 mm.
What's the closest fraction to a size in mm?
When you type in millimeters, the tool shows the closest 1/64 fraction and the difference, which helps when choosing an inch drill bit or wrench.
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.