Free tool · Calculator · Client-side
mm ↔ inch fraction converter
Type millimeters, get decimal inches and the nearest fraction your tape can actually show — with the rounding error stated and signed, so you know what the snap costs. It works the other way too: type 13/16 or 1 3/8 and get millimeters, exactly.
Runs entirely in your browser. Nothing you type is sent anywhere — there is no server on the other end.
No analytics either; the only outside request this page makes is for its font. The math is ordinary arithmetic on the international inch: 1 in = 25.4 mm, exactly.
DECIMAL MILLIMETERS · e.g. 21 or 20.6375
| Snap | Nearest | Error |
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Sign convention: + means the fraction reads over the true size (the part comes out big); − means under. Halves round up.
ACCEPTS: 0.8125 · 13/16 · 1 3/8 · 1-3/8
Fractions convert exactly — 13/16″ is 20.6375 mm, not “about 20.64”. When a value can’t terminate (say 1/3″), the result says ≈ instead of =.
Numbers are half the job — if you’re also staring at the files, the free NC1 viewer and DXF viewer run in your browser the same way: nothing uploaded. And the plate weight calculator takes the same fractions.
Ref · Sixteenths
Sixteenths, in millimeters
Every sixteenth from 1/16″ to 1″, with the exact decimal and the millimeter value to three places. These are computed on this page from 1 in = 25.4 mm — not typed in from a chart.
| Fraction | Inch | mm |
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| Fraction | Inch | mm |
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Millimeter values rounded half-up to three decimals; the fourth decimal is always a 0 or a 5, so nothing here is off by more than 0.0005 mm. Need it exact? Type the fraction into the converter above.