Craft Quantities
Plan & Takeoffs

Measurements & Conversions

Inch Fraction to Millimetres Calculator

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

  • Answers as you type
  • Every formula cited
  • Calculated in your browser
SettingsSettings for this calculationUS
Market
Imperial · sales tax
The measurement in inches, as a decimal.

Enter fractions as decimals: 3/4 is 0.75, 5/16 is 0.3125, 1/32 is 0.03125. The step on this field is one sixty-fourth, so the arrows walk the tape's own graduations rather than arbitrary decimals.

Metric equivalent

19.05 mm

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
1.9 cm
Metres
0.02 m
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

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

Inputs used

Measurement (in)
0.75

Intermediate steps

Inches entered
0.75 in
Nearest sixteenth
0.75 in
Centimetres
1.9 cm
Metres
0.02 m
Final result19.05 mm

Confidence note: 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.

Add the equipment this sizes

This result is a specification — 19.05 mm — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-08-26 · in the site-wide review of 2026-09-06 · v1.0.0

Regulatory standards & verification citations1
  1. International yard and pound agreement (1959) — 1 inch = 25.4 mm exactly, adopted by NIST, BSI and Standards Australia
Cite this page

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.

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.

Now that you have the number

These guides cover the work this quantity is for.

How to calculate inch fraction to millimetres in 2 steps

  1. Measurement (in)The measurement in inches, as a decimal.
  2. Metric equivalentThe tool computes the metric equivalent from those figures and shows the formula, its sources, and a confidence rating alongside it.

Inch Fraction to Millimetres at common values

Page defaults, not your figures above.

Measurement (in)Metric equivalent (mm)
0.0631.59
0.1253.18
0.256.35
0.3759.52
0.512.7
0.62515.9
0.7519
0.87522.2
125.4

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.
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 — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.