mm ⇄ Inch Fraction & Tolerance Converter Community
Questions, answers and tips from people who use the mm ⇄ Inch Fraction & Tolerance Converter. Millimetres to inch fractions with tolerance limits and a batch list.
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From the tool guide: common questions about mm ⇄ Inch Fraction & Tolerance Converter
The items below are not posts by community members. They come from the written guide for this tool and are here to get a conversation started. Use “Ask a follow-up” to open a thread about any of them.
How do I convert mm to a fraction?
Divide by 25.4 to get inches, then round to the nearest 1/n; this tool does it and shows the error.
From the tool guide Ask a follow-upCan it convert fractions to mm?
Yes — type the fraction (3/8") and choose any output.
From the tool guide Ask a follow-upWhat fraction precision should I use?
1/16 for woodworking, 1/64 for machining, decimals for precision parts.
From the tool guide Ask a follow-upIs batch conversion supported?
Yes, one value per line with CSV copy.
From the tool guide Ask a follow-upWhat this tool does
Machinists, woodworkers and CAD users keep running into the same problem: a dimension in millimetres needs to become a fraction on a tape measure, or a fractional drawing needs real millimetres. This converter accepts decimals or fractions (12.7, 3 7/16, 1-1/4, 5/32, 0.5in, 3/8") in millimetres, inches, centimetres, metres or thou, and returns the value in every unit plus the nearest fraction at the precision you choose (halves to 1/128) — together with how far that fraction is from the exact value.
How to use it, step by step
- Type a value (e.g. 12.7 mm or 3 7/16").
- Choose the unit and fraction precision.
- Add a tolerance if the part has one.
- Copy the result or use Batch mode for many values.
Tips from the guide
- Use the finest fraction your tape or caliper can read.
- When tolerances are tight use decimals, not fractions.
- Round toward the safe side (smaller hole, larger shaft).
- Check the error warning when a tolerance is set.
Common mistakes to avoid
- Treating a fraction as exact.
- Forgetting that 1 inch is exactly 25.4 mm.
- Mixing mixed numbers like 1-1/4 with minus signs.
Who uses it
- Machinists and woodworkers. Quickly read fractions off a metric drawing.
- Engineering students. Convert between unit systems with correct rounding.
- Makers. Match metric parts to imperial hardware.
How to ask a question people can answer
A good thread on the mm ⇄ Inch Fraction & Tolerance Converter saves everyone time. Start with a title that names the exact problem, such as the input you used, the result you expected and the result you got. A title like “Not working” is hard to answer, while a title with the specifics gets replies quickly.
- Say what you tried. List the steps you followed and any settings you changed, so replies do not repeat what you already did.
- Share a small example. A short sample input and the output you saw is worth more than a long description. Remove anything private first.
- Mention your setup. Your device, browser and whether you are on a phone or a computer can explain many odd results.
- One question per thread. Separate topics get clearer answers and are easier to find later with the search box above.
- Come back and reply. If a suggestion worked, say so and upvote it, and if you found the fix yourself, post it for the next person.
Community rules
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