Inches to cm: How to Read TV, Bike Wheel and Jeans Sizes

1 inch is 2.54 cm: the definition and a mental-math trick

One inch is 25.4 mm, or 2.54 cm. This is the exact value set by the 1959 international yard and pound agreement, not an approximation. Because the conversion is exact, the math is simple as long as you keep track of the decimal places.

• Inches → cm: inches × 2.54. 40 inches is 40 × 2.54 = 101.6 cm.
• cm → inches: cm ÷ 2.54 (= × 0.3937). 100 cm is about 39.4 inches.
• Mental math: multiply the inches by 2.5, then add 1.6% of that. 10 inches is 25 cm + 0.4 cm = 25.4 cm.
• 10 cm is about 3.94 inches. On a ruler, the cm and inch scales line up at roughly 10:4.

Inches to cm conversion chart

Here are inch sizes you'll often see on electronics and parts. Display and TV sizes are diagonal measurements, so check the right-hand column too.

It helps to memorize one anchor pair. Start from “10 inches = 25.4 cm”: double it for 20 inches = 50.8 cm, halve it for 5 inches = 12.7 cm, and you'll never slip a decimal place even without a calculator.

Getting a TV's width and height from its size

The inch size of a TV or monitor is the length of the screen's diagonal. To decide whether it will fit, you need the width, so convert the diagonal into width and height. For a 16:9 screen, the width is about 0.872 times the diagonal and the height about 0.490 times.

These figures are for the screen area only. Real products add a bezel and a stand, so the overall width is typically 2–5 cm larger than the screen. If the TV will sit on a TV stand, check the “external dimensions” in the spec sheet and the spacing between the stand's feet. For wall mounting, you'll also need the VESA hole spacing.

Bikes, clothing and images measure different things

What an inch figure measures changes from product to product. Before converting to cm, check what dimension it actually describes.

• Bikes: the nominal size of the tire's outer diameter. 26 inches is about 66 cm, but the actual size varies by a few millimeters with the tire standard. The right rider height depends on the frame size, so the wheel size alone isn't enough to choose a bike.
• Trousers and jeans: the 30 in W30 is the waist in inches, 30 × 2.54 ≈ 76 cm. L is the inseam (length): L32 is about 81 cm. Actual measurements can differ from the label depending on the brand.
• Monitors and phones: the screen diagonal. It doesn't include the bezel, so check the body size separately.
• Car wheels and tires: a size like 17 inches is the wheel (rim) diameter, not the tire's outer diameter.
• Plumbing: a “1-inch” nominal pipe size is a standard name, not the actual inner or outer diameter. Choosing by the literal measurement will give you the wrong fit.

The dpi (dots per inch) you see in images and printing is also a density: how many dots fit in one inch. To print at 350 dpi, you need 350 pixels for every inch (2.54 cm). How to work out the pixels needed for A4 or postcard prints is covered in Image dpi and resolution.

Shaku, sun and ken: Japan's traditional length units

Japanese architecture and kimono still use the traditional shakkanhō length units. Under Japan's Measurement Act, 1 shaku is 10/33 m, or about 30.303 cm, very close to a foot (30.48 cm).

Japanese house plans talk about a “910 mm module” because they're based on half a ken (3 shaku ≈ 91 cm). 1 ken × 1 ken is 1 tsubo, so converting tsubo and square meters also comes from the shaku. Note that the kujira-jaku (whale shaku) used for kimono measurements is a different length, about 37.9 cm per shaku, so don't mix it up with the building shaku.

1. 1

   Choose “Length” in the Unit Converter

   It starts on inches → cm. Tap the swap button to switch to cm → inches.

2. 2

   Enter a value and read the list

   mm, cm, m, inches, feet, yards, miles, nautical miles, shaku, sun and ken are shown all at once, which is handy when moving between drawings and foreign measurements.

3. 3

   Copy the quick-reference table

   Copy a table of 1, 2, 3, 5, 10 and so on as-is and paste it into a shopping note or order form.

FAQ

How many centimeters is 1 inch?

Exactly 2.54 cm (25.4 mm). This value was defined by the 1959 international yard and pound agreement, so it isn't a rounded approximation. To go from inches to cm, multiply by 2.54; from cm to inches, divide by 2.54 (or multiply by 0.3937). For mental math, multiply by 2.5 and add about 1.6%, which is accurate enough for everyday use.

How big is a 32-inch TV in centimeters?

The diagonal is 81.3 cm. What you need to decide where it goes, though, is the width: for a 16:9 screen, the screen area is about 70.8 × 39.9 cm. The overall width including the bezel and stand is usually 2–5 cm more. When deciding whether it fits on a TV stand, check the external dimensions in the spec sheet and the spacing of the stand's feet.

How wide is a 55-inch TV?

For a 16:9 screen, the diagonal is 139.7 cm, the width about 121.8 cm and the height about 68.5 cm. Since the width is about 0.872 times the diagonal, you can use the same calculation for any size. When wall-mounting or fitting it on a shelf, leave a few extra centimeters on each side for cables. For viewing distance, around 1.5 times the screen height is a common guideline for 4K.

What is a 30-inch waist in centimeters?

30 × 2.54 ≈ 76 cm. A 32-inch waist is about 81 cm and a 34-inch waist about 86 cm. Even with the same label, actual measurements can differ by 2–3 cm between brands and models. Measure the waist of a pair you own laid flat and compare against that to avoid mistakes. The L number is the inseam length.

How do I convert centimeters to inches?

Divide the centimeters by 2.54, or multiply by 0.3937. For example, 60 cm is 60 ÷ 2.54 ≈ 23.6 inches, and 170 cm is about 66.9 inches. To express height in feet and inches, convert to inches first, then divide by 12: the quotient is feet and the remainder inches. 170 cm is about 5 feet 7 inches.