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Inch Fraction to Millimetres Calculator

Convert an inch measurement — including sixteenths and thirty-seconds — into millimetres for metric drawings and tooling.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Metric equivalent

0.75 in

High confidence

1 inch = 25.4 mm exactly, by international agreement since 1959. Exact by definition. Round to the tolerance the work needs — quoting 19.0500 mm for a 3/4 in timber implies a precision the material does not have.

Inches entered
0.75 in
Nearest sixteenth
0.75 in
Centimetres
0.75 in
Metres
0.06 ft

Imperial stock meeting a metric drawing is a daily occurrence on refurbishment: existing fabric measured in inches, new components specified in millimetres. Getting this wrong by a sixteenth is 1.6 mm, which is invisible on a wall and fatal on a machined fit.

Add the equipment this sizes

This result is a specification — 0.75 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • International yard and pound agreement (1959) — 1 inch = 25.4 mm exactly, adopted by NIST, BSI and Standards Australia

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

How do I enter a fraction like 7/8?
Divide it: 7 ÷ 8 = 0.875. The common ones are worth memorising — 1/16 is 0.0625, 1/8 is 0.125, 1/4 is 0.25, 3/8 is 0.375, 1/2 is 0.5, 5/8 is 0.625, 3/4 is 0.75, 7/8 is 0.875.
Is 25.4 an approximation?
No. Since 1959 the inch has been defined as exactly 25.4 mm, so the conversion introduces no error at all. Any discrepancy on site is measurement or manufacturing tolerance, never arithmetic.
Why does a 3/4 inch pipe not measure 19.05 mm?
Because nominal pipe sizes are names, not dimensions. A 3/4 in copper tube has an outside diameter around 22 mm in the UK and 19 mm in the US, and neither is the nominal figure. Convert the measured dimension, never the trade size.
What is the metric equivalent of a sixteenth?
1/16 in is 1.5875 mm — near enough 1.6 mm for most work, and worth knowing because it is roughly the smallest division on an imperial tape. If a drawing tolerances something tighter than that, an imperial tape is not the right instrument.