Inches to Fraction Calculator
Convert decimal inches to the nearest fractional inch (1/2, 1/4, 1/8, up to 1/128), plus millimetres and centimetres.
Reviewed October 7, 2026 Runs in your browser — inputs are never stored
Fractional inches
3 3/8 in
Millimetres
85.725000 mm
Centimetres
8.572500 cm
This tool provides general unit conversions for everyday and educational use. For regulated, legal, or scientific applications, verify conversion factors against the applicable official standard.
About the Inches to Fraction Calculator
The inches to fraction calculator turns a decimal inch value into the nearest fraction a tape measure can show. You choose the finest division you can read — halves down to 1/128 — and the tool rounds to the closest fraction, simplifies it and shows the rounding error and the metric equivalent. It is useful when a plan or CAD drawing gives decimals but your rule is marked in fractions.
How to use it
- 1Enter the decimal inch value.
- 2Choose the smallest fraction your ruler or tape shows (for example 1/16).
- 3Read the nearest fraction, the error and the value in millimetres.
- 4Copy, share or print the result with the buttons below it.
Worked example
3.375 in is exactly 3 3/8 in. A value of 2.3125 in is 2 5/16 in to the nearest 1/16.
How it works
How it works
The decimal portion of the input is compared against all fractions up to the chosen denominator. The closest match within a half-unit tolerance is returned.
Common fractional equivalents
| Decimal | Fraction | mm |
|---|---|---|
| 0.125 | 1/8 | 3.175 |
| 0.25 | 1/4 | 6.35 |
| 0.375 | 3/8 | 9.525 |
| 0.5 | 1/2 | 12.7 |
| 0.625 | 5/8 | 15.875 |
| 0.75 | 3/4 | 19.05 |
| 0.875 | 7/8 | 22.225 |
Common use cases
- Marking decimal measurements on a tape measure
- Reading machinist drawings
- Converting drill and bolt sizes
Frequently asked questions
A:For woodworking, 1/16 or 1/32 is typical. For precision machining, 1/64 or 1/128 is common.
A:The calculator returns the closest fraction within a half-denominator-unit tolerance.
Reviewed for accuracy · Last updated October 7, 2026
Conversion factors are based on internationally defined SI units and standard metric/imperial equivalence tables.
CalcWisee Editorial Team
Calculator development and formula review
CalcWisee is an independent site founded by Ayman. Every calculator is built from a published formula or official definition, tested against hand-worked examples before it goes live, and corrected promptly when a reader reports an issue to ayman@calcwisee.com.
Expertise: Financial mathematics, Health and fitness formulas, Applied mathematics, Unit conversion standards
References & sources
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