Convert Inch to Millimetre
1 inch = 25.4 millimetre (mm). For example, 10 inch = 254 millimetre and 100 inch = 2,540 millimetre. Type any value below to convert inch to millimetre both ways — it runs entirely in your browser.
Quick answer: Inch to Millimetre
1 Inch = 25.4 Millimetre (in → mm). To convert inch to millimetre, multiply by 25.4. To convert millimetre to inch, multiply by 0.03937008. The converter at the top does this instantly and both ways; the sections below give the formula, worked examples, a full conversion chart and answers to the most common inch-to-millimetre questions.
How to convert Inch to Millimetre
To convert inch to millimetre, multiply the number of inch by the conversion factor 25.4, because 1 in = 25.4 mm. The conversion is linear, so the same factor works for any value — whole numbers, decimals or fractions. For the reverse direction, 1 mm = 0.03937008 in, so you divide by 25.4 (or multiply by 0.03937008) to turn millimetre back into inch.
mm = in × 25.4 ·
in = mm × 0.03937008
- Write down the value you want to convert, in inch.
- Multiply it by 25.4.
- The result is the same area/length/quantity expressed in millimetre.
Inch to Millimetre — worked examples
Each row shows the exact arithmetic so you can follow the conversion step by step. For example, 5 inch is 127 millimetre because 5 in × 25.4 = 127 mm.
| Inch | Calculation | Millimetre |
|---|---|---|
| 1 in | 1 in × 25.4 = 25.4 mm | 25.4 mm |
| 2 in | 2 in × 25.4 = 50.8 mm | 50.8 mm |
| 3 in | 3 in × 25.4 = 76.2 mm | 76.2 mm |
| 5 in | 5 in × 25.4 = 127 mm | 127 mm |
| 7 in | 7 in × 25.4 = 177.8 mm | 177.8 mm |
| 10 in | 10 in × 25.4 = 254 mm | 254 mm |
| 12 in | 12 in × 25.4 = 304.8 mm | 304.8 mm |
| 15 in | 15 in × 25.4 = 381 mm | 381 mm |
| 20 in | 20 in × 25.4 = 508 mm | 508 mm |
| 25 in | 25 in × 25.4 = 635 mm | 635 mm |
| 50 in | 50 in × 25.4 = 1,270 mm | 1,270 mm |
| 100 in | 100 in × 25.4 = 2,540 mm | 2,540 mm |
Common Inch to Millimetre conversions
These are the inch-to-millimetre values people look up most often. Every figure is computed from the exact factor, so you can rely on them for quick reference:
- 1 inch = 25.4 millimetre
- 2 inch = 50.8 millimetre
- 2.5 inch = 63.5 millimetre
- 3 inch = 76.2 millimetre
- 4 inch = 101.6 millimetre
- 5 inch = 127 millimetre
- 6 inch = 152.4 millimetre
- 7 inch = 177.8 millimetre
- 8 inch = 203.2 millimetre
- 9 inch = 228.6 millimetre
- 10 inch = 254 millimetre
- 12 inch = 304.8 millimetre
- 15 inch = 381 millimetre
- 20 inch = 508 millimetre
- 25 inch = 635 millimetre
- 30 inch = 762 millimetre
- 50 inch = 1,270 millimetre
- 75 inch = 1,905 millimetre
- 100 inch = 2,540 millimetre
- 200 inch = 5,080 millimetre
- 500 inch = 12,700 millimetre
- 1000 inch = 25,400 millimetre
Inch to Millimetre conversion chart (both directions)
The chart below converts inch to millimetre and millimetre to inch side by side, so it works whichever way you need. 1 inch = 25.4 millimetre, and 1 millimetre = 0.03937008 inch.
| Inch → Millimetre | Millimetre → Inch |
|---|---|
| 0.25 in = 6.35 mm | 0.25 mm = 0.00984252 in |
| 0.5 in = 12.7 mm | 0.5 mm = 0.01968504 in |
| 1 in = 25.4 mm | 1 mm = 0.03937008 in |
| 2 in = 50.8 mm | 2 mm = 0.07874016 in |
| 3 in = 76.2 mm | 3 mm = 0.1181102 in |
| 4 in = 101.6 mm | 4 mm = 0.1574803 in |
| 5 in = 127 mm | 5 mm = 0.1968504 in |
| 6 in = 152.4 mm | 6 mm = 0.2362205 in |
| 7 in = 177.8 mm | 7 mm = 0.2755906 in |
| 8 in = 203.2 mm | 8 mm = 0.3149606 in |
| 9 in = 228.6 mm | 9 mm = 0.3543307 in |
| 10 in = 254 mm | 10 mm = 0.3937008 in |
| 12 in = 304.8 mm | 12 mm = 0.4724409 in |
| 15 in = 381 mm | 15 mm = 0.5905512 in |
| 20 in = 508 mm | 20 mm = 0.7874016 in |
| 25 in = 635 mm | 25 mm = 0.984252 in |
| 30 in = 762 mm | 30 mm = 1.181102 in |
| 40 in = 1,016 mm | 40 mm = 1.574803 in |
| 50 in = 1,270 mm | 50 mm = 1.968504 in |
| 75 in = 1,905 mm | 75 mm = 2.952756 in |
| 100 in = 2,540 mm | 100 mm = 3.937008 in |
| 150 in = 3,810 mm | 150 mm = 5.905512 in |
| 200 in = 5,080 mm | 200 mm = 7.874016 in |
| 250 in = 6,350 mm | 250 mm = 9.84252 in |
| 500 in = 12,700 mm | 500 mm = 19.68504 in |
| 1000 in = 25,400 mm | 1000 mm = 39.37008 in |
Inch vs Millimetre: which is bigger?
A inch is the larger unit: one inch equals 25.4 millimetres. Put another way, you need 25.4 millimetres to make a single inch.
What is a Inch? History, origin and usage
The inch takes its name from the Latin uncia, 'a twelfth part', because it was one-twelfth of a Roman foot, the same root that gave English the word 'ounce'. It was also understood as the width of a man's thumb, and one medieval English rule averaged the thumb-breadths of three different men.
The inch is used in the US, UK and Canada for screen sizes, paper, body measurements and countless engineering contexts. Since 1959 it is defined as exactly 2.54 centimetres.
An old English statute defined the inch as three barleycorns laid end to end, a standard that even shaped shoe sizing. Screen, tyre and wheel sizes are still quoted in inches almost everywhere in the world.
What is a Millimetre? History, origin and usage
The millimetre is one-thousandth of a metre, taking its prefix from the Latin mille, 'thousand'. Like the other metric submultiples it dates to the French metric reform of the 1790s.
The millimetre is the workhorse of engineering drawings, machining and manufacturing, where tolerances are specified in millimetres or fractions of them. It is also the standard unit for rainfall and snowfall depth in meteorology.
Rainfall reported in 'millimetres' is the depth water would reach on a flat surface, so one millimetre of rain equals one litre per square metre. The smallest markings on most metric rulers are millimetres.
Convert 1 Inch to other units
It can help to see a inch next to the other units it is commonly compared with. One inch (in) is equal to:
| 1 Inch equals | Unit |
|---|---|
| 0.0000254 km | Kilometre |
| 0.0254 m | Metre |
| 0.254 dm | Decimetre |
| 2.54 cm | Centimetre |
| 25.4 mm | Millimetre |
| 25,400 µm | Micrometre |
| 0.00001578283 mi | Mile |
| 0.02777778 yd | Yard |
| 0.08333333 ft | Foot |
| 0.0000137149 nmi | Nautical Mile |
| 0.0001262626 fur | Furlong |
| 0.001262626 ch | Chain |
| 0.1262626 li | Link |
| 0.005050505 rd | Rod |
| 0.005050505 pole | Pole |
| 0.01388889 ftm | Fathom |
| 0.25 hand | Hand |
| 0.1111111 span | Span |
| 0.2222222 finger | Finger |
| 0.05555556 cubit | Cubit |
| 0.004166667 rope | Rope |
| 0.01397 ken | Ken |
| 0.000005260943 lea | League |
| 72 pt | Point |
| 0.0000000000001697885 AU | Astronomical Unit |
| 0.000000000000000002684782 ly | Light-year |
| 0.00254 dam | Decametre |
| 0.000254 hm | Hectometre |
| 0.000004571634 nl | Nautical League |
Convert 1 Millimetre to other units
One millimetre (mm) is equal to:
| 1 Millimetre equals | Unit |
|---|---|
| 0.000001 km | Kilometre |
| 0.001 m | Metre |
| 0.01 dm | Decimetre |
| 0.1 cm | Centimetre |
| 1,000 µm | Micrometre |
| 0.0000006213712 mi | Mile |
| 0.001093613 yd | Yard |
| 0.00328084 ft | Foot |
| 0.03937008 in | Inch |
| 0.0000005399568 nmi | Nautical Mile |
| 0.00000497097 fur | Furlong |
| 0.0000497097 ch | Chain |
| 0.00497097 li | Link |
| 0.0001988388 rd | Rod |
| 0.0001988388 pole | Pole |
| 0.0005468066 ftm | Fathom |
| 0.00984252 hand | Hand |
| 0.004374453 span | Span |
| 0.008748906 finger | Finger |
| 0.002187227 cubit | Cubit |
| 0.000164042 rope | Rope |
| 0.00055 ken | Ken |
| 0.0000002071237 lea | League |
| 2.834646 pt | Point |
| 0.000000000000006684587 AU | Astronomical Unit |
| 0.0000000000000000001057001 ly | Light-year |
| 0.0001 dam | Decametre |
| 0.00001 hm | Hectometre |
| 0.0000001799856 nl | Nautical League |
Tips for converting Inch to Millimetre
- To go from inch to millimetre, multiply by 25.4; to go back, divide by 25.4 (or multiply by 0.03937008).
- For a quick mental estimate, remember that 1 inch ≈ 25.4 millimetre, so 10 inch ≈ 254 millimetre.
- The converter above keeps full precision; the tables round for readability, so use the tool for exact figures.
- Both fields update live as you type — change either side to convert in that direction.
How to use this Inch to Millimetre converter
Type a number into the Inch field and the equivalent in Millimetre appears instantly — there is no “convert” button to press and nothing is sent to a server, so it works offline once the page has loaded and is safe for any data. You can also type into the Millimetre field to convert the other way (millimetre to inch). Use the swap control to flip the two units, and copy the result with a single click. Because the calculation runs in your browser with full floating-point precision, the converter is more exact than the rounded figures shown in the reference chart above — use the chart for quick look-ups and the tool for precise work.
Accuracy and method
Every figure on this page — the formula, the worked examples, the conversion chart and the “convert to other units” tables — is computed from a single verified conversion factor (1 in = 25.4 mm), never copied from a hand-typed lookup table that could drift. That factor is derived from each unit’s definition in terms of a common base unit, and an automated check re-verifies all of the site’s factors on every update, so the numbers here stay correct over time. This matters for inch-to-millimetre conversions because a small rounding error in a published table compounds quickly at larger quantities; computing from the exact factor avoids that.
Sources
- NIST Special Publication 811 — Guide for the Use of the SI — publishes the exact metric equivalents of the customary units. The inch, foot, yard and mile are defined exactly in metres by the 1959 international yard-and-pound agreement, so every imperial figure on this page is exact, not rounded.
- BIPM — The International System of Units (SI Brochure) — the defining document for the SI, published by the International Bureau of Weights and Measures. It fixes the base unit that this conversion resolves to, which is why the factor here can be exact rather than approximate.
The metric units (km, m, cm, mm, µm) are exact by definition, and the imperial units (mile, yard, foot, inch, nautical mile) use their exact international values. Traditional units (hand, span, finger, cubit, rod/pole, link, rope, ken, league) are given at their commonly accepted standard sizes — historical local values sometimes differed, so confirm against a primary source before relying on them for legal or historical work.
Frequently asked questions
- How many millimetre are in 1 inch?
- 1 inch = 25.4 millimetre (mm). To convert any number of inch to millimetre, multiply by 25.4.
- How do I convert inch to millimetre?
- Multiply the number of inch by 25.4. For example, 10 inch = 10 × 25.4 = 254 millimetre, and 25 inch = 635 millimetre.
- How many inch are in 1 millimetre?
- 1 millimetre = 0.03937008 inch. So to convert millimetre back to inch, multiply by 0.03937008.
- What is the formula to convert inch to millimetre?
- millimetre = inch × 25.4. The reverse formula is inch = millimetre × 0.03937008.
- How much is 100 inch in millimetre?
- 100 inch = 2,540 millimetre. (And 1000 inch = 25,400 millimetre.)
- Which is bigger, a inch or a millimetre?
- A inch is larger: 1 inch = 25.4 millimetre.
- Is this inch to millimetre converter accurate?
- Yes — every value is computed from the exact 25.4 mm per in factor (not rounded look-up tables), and the factors are re-verified automatically on every update.
- Can I convert millimetre to inch too?
- Yes. The converter works both ways — enter a value in either field. 1 millimetre = 0.03937008 inch.