Article — Inches to cm Converter
Inches to centimeters — the conversion and where it shows up
One inch equals exactly 2.54 centimeters. To convert inches to centimeters, multiply by 2.54. To convert centimeters to inches, divide by 2.54. A 6-foot person is 72 inches or 182.88 cm. A 55-inch TV is 139.7 cm diagonal. A US Letter sheet is 21.59 cm × 27.94 cm.
The factor is not a rounded measurement — it is a defined value, fixed by the 1959 International Yard and Pound Agreement. The treaty made the inch identical to 25.4 millimeters by definition, so every modern inch conversion is exact to whatever precision the math is carried out to.
The factor: 2.54 cm per inch, exactly
The conversion is one multiplication. Inches × 2.54 = centimeters. Centimeters ÷ 2.54 = inches.
1 in = 2.54 cm1 ft (12 in) = 30.48 cm1 yd (36 in) = 91.44 cm1 mile (63,360 in) = 160,934 cm1 cm = 0.3937 in1 m = 39.3701 inFor mental math: multiply inches by 2.5 to get a rough centimeter value, then add 1.6% for the exact answer. 10 in × 2.5 = 25, + 0.4 (about 1.6%) = 25.4 cm. Going the other way: divide centimeters by 2.5 and subtract 1.6%. 100 cm ÷ 2.5 = 40 in, − 0.6 ≈ 39.37 in.
Height conversion
The most common reason people convert inches to centimeters is height. A US driver's license lists height in feet and inches; a European passport, medical record, or athletic registration uses centimeters.
The conversion: take total inches (feet × 12 + extra inches) and multiply by 2.54. 5 ft 10 in = 70 inches = 177.80 cm. 6 ft = 72 inches = 182.88 cm. 5 ft 6 in = 66 inches = 167.64 cm.
- 5'0" = 60 in = 152.40 cm
- 5'4" = 64 in = 162.56 cm (US median female)
- 5'6" = 66 in = 167.64 cm
- 5'9" = 69 in = 175.26 cm (US median male)
- 6'0" = 72 in = 182.88 cm
- 6'4" = 76 in = 193.04 cm
- 6'6" = 78 in = 198.12 cm (NBA average height)
The CDC's National Health and Nutrition Examination Survey reports US adult average heights of 175.4 cm (men, 5'9") and 161.7 cm (women, 5'3.5"). The Dutch and northern Europeans are taller on average; East and South Asian averages are shorter.
TV and monitor diagonals
TVs are sold by their diagonal screen measurement in inches, even in metric countries. The size is the corner-to-corner distance, not the width.
A 55-inch TV at the standard 16:9 aspect ratio is 55 inches diagonal, which works out to about 48 in (122 cm) wide and 27 in (68 cm) tall. A 65-inch TV at 16:9 is about 57 in (145 cm) wide. The math: width = diagonal × 16 / √(16² + 9²) = diagonal × 0.872; height = diagonal × 0.490.
The "TV inch" used to be a rough number — early CRT manufacturers measured the tube envelope, not the visible screen. A 25-inch CRT might show only 23 inches of picture. Since the early 2000s, US Federal Trade Commission guidance has required manufacturers to specify the visible diagonal, which now matches the advertised inch count exactly.
Monitor sizes follow the same convention. A 27-inch monitor is 27 inches (68.58 cm) diagonal. Laptop screens range from 11 inches (27.94 cm) for ultraportables to 17 inches (43.18 cm) for desktop-replacement gaming laptops.
Shoe sizes
Shoe sizes hide an inch-to-centimeter conversion under their numbering schemes. US shoe sizes use a "barleycorn" scale where each size step is 1/3 of an inch (8.47 mm). European shoe sizes use the Paris point: 2/3 of a centimeter (6.67 mm) per size step. The two scales are not parallel — a single US size step is 1.27 European sizes.
A US men's size 10 corresponds to a foot about 27.0 cm long, which fits roughly a European 43. A US women's size 8 is about 24.6 cm = European 38-39. The actual conversion depends on the brand because of last shape and toe room.
- US men 9 = 27 cm foot = EU 42
- US men 10 = 27.9 cm foot = EU 43
- US men 11 = 28.6 cm foot = EU 44-45
- US women 7 = 23.5 cm = EU 37-38
- US women 8 = 24.1 cm = EU 38-39
- US women 9 = 25.4 cm = EU 39-40
Paper sizes — US Letter vs A4
US Letter is 8.5 × 11 inches = 21.59 × 27.94 cm. A4 is 21.0 × 29.7 cm = 8.27 × 11.69 inches. The two are close but not interchangeable: A4 is 0.2 inches narrower and 0.7 inches taller than US Letter.
Printers in metric countries default to A4; printers in the US default to Letter. Documents formatted for one paper size and printed on the other typically end up with cropped margins or shifted page breaks. The PDF standard sidesteps the problem by embedding the page size into each file.
If you are sending a document internationally, set page size to A4 and use 1-inch (2.54 cm) margins. Letter-printed copy will still fit on A4 with a slight bottom margin shift, and A4-printed copy looks fine on Letter.
Fractional inches
US tape measures and engineering drawings still use fractional inches, divided by powers of two: 1/2, 1/4, 1/8, 1/16, 1/32, 1/64. The fractions are not arbitrary — they let you fold a length in half repeatedly to find any subdivision without arithmetic.
A 1/16 inch is 1.5875 mm. A 1/32 inch is 0.794 mm — close enough to one millimeter (within 21%) that metric and imperial tape measures often agree to the nearest tick. Common fractional sizes in hardware:
1/16 in = 0.159 cm1/8 in = 0.318 cm1/4 in = 0.635 cm3/8 in = 0.953 cm1/2 in = 1.270 cm5/8 in = 1.588 cm3/4 in = 1.905 cm7/8 in = 2.223 cmThe 1959 treaty
Before 1959 the inch had different definitions in different countries. The US Survey Inch was based on the 1893 Mendenhall Order, which defined the meter as 39.37 inches — equivalent to 1 inch = 25.4000508 mm. The British imperial inch was slightly different again, descending from a separate yard standard kept at the Tower of London.
In 1959, six English-speaking nations — the US, UK, Canada, Australia, New Zealand, and South Africa — signed the International Yard and Pound Agreement. It defined the yard as exactly 0.9144 meters, which made the inch exactly 25.4 millimeters = 2.54 cm. The new value was a clean number, deliberately chosen halfway between the older US and UK inches.
The US kept the old US Survey Foot for geodetic surveying — bridges, state plane coordinates, land titles — because changing it would have invalidated millions of legal documents. The Survey Foot was officially retired on January 1, 2023, after a 64-year transition.
If you are working with US geodetic data or old land surveys, watch for the unit. 1 US Survey Foot = 1,200/3,937 m ≈ 0.30480061 m, versus the modern International Foot = 0.3048 m exactly. The difference is 2 parts per million — about 0.2 mm per kilometer — which compounds noticeably over large state-scale projects.
Mistakes to avoid
Three things go wrong when converting between inches and centimeters.
First, confusing fraction notation. 3/8 inch is 0.375 inches, not 0.38. Fractional inches are exact ratios; rounding them as decimals introduces small errors that compound in multi-step calculations.
Second, treating diagonal as width. A 55-inch TV is 55 inches corner-to-corner; the visible width is only 48 inches. If you are planning wall space, look up the cabinet width — manufacturers list it separately.
Third, mixing US Survey Foot with International Foot for long distances. A 1-mile (5,280-foot) survey done in Survey Feet ends up about 0.01 feet (3 mm) longer than the same mile in International Feet. Negligible for most uses, but enough to misalign property boundaries.