mm ⇄ Inch Fraction & Tolerance Converter
Millimetres to inch fractions with tolerance limits and a batch list · free, no signup
See mm ⇄ Inch Fraction & Tolerance Converter in action
Free mm ⇄ Inch Fraction Converter with Tolerances
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.
Because a fraction is only an approximation, the tool is tolerance-aware: enter a symmetric or asymmetric tolerance and it computes the minimum and maximum limits in millimetres, decimal inches and fractions, and warns when the rounding error of the fraction exceeds your tolerance. Batch mode converts a whole list of values at once and copies it as CSV, and a 1/64 fraction chart gives the decimal and mm for every step up to 1".
Key features
Any input format
Decimals, fractions and mixed numbers, with or without units.
Nearest fraction + error
1/2 to 1/128 with the exact rounding error in mm.
Tolerance limits
Min/max in mm, inches and fractions; warns when rounding exceeds tolerance.
Batch + chart
List conversion with CSV copy and a 1/64 chart.
How to use it
- 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.
Worked example
Example
19.05 mm = 0.75 in = 3/4" exactly. 12 mm = 0.47244 in ≈ 15/32" (−0.0 error to 1/32 precision is +0.1 mm). With ±0.1 mm tolerance the limits are 11.9–12.1 mm = 0.4685–0.4764 in.
Who uses this tool
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.
Tips for the best results
- 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.
Why use AZRS QuickFix?
It is 100% free, needs no signup and has no watermark or usage limits. The tool runs in your browser, so what you type stays on your device, and it works on phones, tablets and desktops. New tools are added every week — bookmark this page or browse the full QuickFix toolbox.
Frequently asked questions
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.
Can it convert fractions to mm?
Yes — type the fraction (3/8") and choose any output.
What fraction precision should I use?
1/16 for woodworking, 1/64 for machining, decimals for precision parts.
Is batch conversion supported?
Yes, one value per line with CSV copy.