Inches to Centimetres Quick Reference

The inch and the centimetre belong to two different measurement systems used by two halves of the world. If you live in the US (or Liberia or Myanmar — the only other countries that haven’t officially adopted metric), you grew up with inches. Everyone else uses centimetres. The conversion comes up constantly: clothing sizes, screen diagonals, lumber dimensions, IKEA instructions, international shipping.

This page is the quick reference for converting between them, including a chart of the common values you’ll actually use.

The formula

One inch equals exactly 2.54 centimetres.

It’s exact, not an approximation. The international inch has been defined as 25.4 millimetres since 1959, when the US, UK, Canada, Australia, New Zealand, and South Africa agreed on a unified definition of the yard and pound. Before that, different countries used slightly different inch values, which is why old engineering specs sometimes don’t line up.

To convert inches → centimetres: multiply by 2.54. To convert centimetres → inches: divide by 2.54 (or multiply by 0.3937).

inches × 2.54 = centimetres
centimetres × 0.3937 = inches

Quick mental math

For rough conversions in your head:

• 1 inch ≈ 2.5 cm (close enough for clothing, screens, casual reference)
• 10 inches ≈ 25 cm
• An inch is roughly the width of a thumb (this is literally where the name comes from)
• A 12-inch ruler ≈ 30 cm (specifically, 30.48 cm)
• A 6-foot person ≈ 183 cm

The 2.5 shortcut is accurate within ~2%. If you need precision, use the exact 2.54.

Inches to centimetres chart

Inches	Centimetres	Inches	Centimetres
1	2.54 cm	18	45.72 cm
2	5.08 cm	20	50.80 cm
3	7.62 cm	24	60.96 cm
4	10.16 cm	27	68.58 cm
5	12.70 cm	30	76.20 cm
6	15.24 cm	32	81.28 cm
7	17.78 cm	36	91.44 cm
8	20.32 cm	40	101.60 cm
9	22.86 cm	48	121.92 cm
10	25.40 cm	50	127.00 cm
11	27.94 cm	60	152.40 cm
12	30.48 cm	72	182.88 cm
14	35.56 cm	80	203.20 cm
15	38.10 cm	96	243.84 cm
16	40.64 cm	100	254.00 cm

For values not on this chart — including fractional inches like 5.75 or 11.5 — use the inch-to-cm converter. It returns the exact result in centimetres, millimetres, metres, and a feet-and-inches breakdown all at once.

Centimetres to inches chart

Centimetres	Inches	Centimetres	Inches
1	0.39 in	50	19.69 in
5	1.97 in	60	23.62 in
10	3.94 in	75	29.53 in
15	5.91 in	80	31.50 in
20	7.87 in	90	35.43 in
25	9.84 in	100	39.37 in
30	11.81 in	120	47.24 in
35	13.78 in	150	59.06 in
40	15.75 in	170	66.93 in
45	17.72 in	180	70.87 in
50	19.69 in	200	78.74 in

Where this conversion comes up

Clothing sizes

International clothing tags are a mess. A waist measurement in the US is given in inches (32, 34, 36). In Europe, it’s centimetres (81, 86, 91). Knowing the rough equivalence makes shopping abroad less of a guessing game.

US waist	EU waist
28 in	71 cm
30 in	76 cm
32 in	81 cm
34 in	86 cm
36 in	91 cm
38 in	97 cm
40 in	102 cm

Shoe sizes follow a completely different system (length in cm for the EU and Japan, an arbitrary numeric scale for the US and UK). For shoes, look up the brand’s specific conversion chart — the foot length in cm is the only reliable common ground.

Screen and display sizes

TVs, monitors, laptops, and tablets are almost universally measured in inches by their diagonal. A “65-inch TV” is 65 inches corner-to-corner, regardless of country. But the physical dimensions (and the space it’ll take on your wall) often need to be in centimetres when you’re measuring a room.

Common screen sizes:

Screen (in)	Diagonal (cm)	Approximate width (cm, 16:9)
13	33.0	28.8
14	35.6	31.0
15.6	39.6	34.5
21	53.3	46.5
24	61.0	53.1
27	68.6	59.8
32	81.3	70.9
43	109.2	95.2
55	139.7	121.8
65	165.1	143.9
75	190.5	166.0
85	215.9	188.2

The width column assumes a standard 16:9 aspect ratio. For ultrawide monitors (21:9) or older 4:3 displays, the width-to-diagonal ratio is different.

Construction and DIY

Lumber, plumbing, and many home-improvement products use inches even in metric countries — it’s a legacy of US manufacturing dominance through the 20th century. A “2×4” plank is actually 1.5 inches by 3.5 inches (3.81 cm × 8.89 cm), because lumber sizes are nominal not actual. Pipe diameters are quoted in inches almost everywhere.

For carpentry, work in the system the materials are sold in. Mixing inches and centimetres in the same project is how mistakes happen.

Print and design

Paper sizes are split: A-series (A4, A3, A2) are metric. Letter and Legal are imperial.

Format	Dimensions (in)	Dimensions (cm)
A4	8.27 × 11.69	21.0 × 29.7
A3	11.69 × 16.54	29.7 × 42.0
US Letter	8.5 × 11	21.6 × 27.9
US Legal	8.5 × 14	21.6 × 35.6

Most printers handle both, but the physical paper is one or the other — make sure the document size matches the paper size or you’ll get scaling or cropping.

The 25.4 mm thing

Engineers and machinists often work in millimetres rather than centimetres. The exact conversion is 1 inch = 25.4 millimetres, and many precision specs are given in mm regardless of which country the part is from. If you’re reading a technical drawing or 3D-printing tolerance and you see numbers like “12.7” or “25.4,” it’s an inch value translated.

CNC machines, 3D printers, and most engineering software accept input in either system but internally calculate in one. If you import a model with imperial dimensions into a metric workspace, every measurement will be off by a factor of 25.4 — which is the most common source of “why is my print 25× too small” bugs.

When the difference matters

For everyday tasks (rough sizing, casual reference) the inch-to-cm conversion is so close to ×2.5 that mental math is fine. For anything precise — carpentry cuts, engineering specs, 3D printing, custom-tailored clothing — use the exact 2.54 multiplier and the inch-to-cm converter for the result with full decimal precision.

For converting back the other way, the same tool works as a cm to inch converter — just enter a centimetre value to see the inches equivalent alongside the other unit conversions.