Inches to Centimeters Converter

The inch and the centimetre are the two short-length units used worldwide for everyday measurements: screen sizes, paper sizes, body measurements, fabric dimensions and many industrial specifications. One international inch = exactly 2.54 centimetres, fixed by the international yard-and-pound agreement of 1 July 1959 among the United States, United Kingdom, Canada, Australia, New Zealand and South Africa. The same agreement fixed the yard at 0.9144 m exactly and the foot at 0.3048 m exactly, which makes the inch equal to 0.0254 m exactly, no rounding.

This converter works in both directions: type a value into either field and the other updates. It includes common presets for screen sizes (6 in phone display, 24 in monitor), paper sizes (A4 = 8.27 × 11.69 in / 21 × 29.7 cm, US Letter = 8.5 × 11 in / 21.59 × 27.94 cm), and fabric/foot lengths (1 ft = 12 in = 30.48 cm). Bonus read-outs give the equivalent in millimetres, metres, feet and yards so one calculation handles most length-conversion needs.

Important: This converter uses the international inch (25.4 mm exactly), which is the standard since 1959. The older US "survey inch" (25.4000508 mm) was used in some pre-1959 land surveys and is slightly different. Most modern contexts use the international inch only.

How to Use

1. Inches (in), enter any non-negative number of inches. Decimal input is fine (e.g. 8.5 for an 8.5-inch tablet).
2. Centimetres (cm), enter any non-negative number of centimetres. The other field updates automatically based on the exact factor 1 in = 2.54 cm.
3. The result block shows the conversion in cm and m, plus the equivalent in feet, yards and mm (so a 24-inch monitor is also 60.96 cm = 0.6096 m = 2 ft = 0.667 yd).
4. Use the presets for common lengths, 6 in (15.24 cm), 1 ft (30.48 cm), A4 short edge (8.27 in / 21 cm), A4 long edge (11.69 in / 29.7 cm), US Letter (8.5 × 11 in), 1 yard (36 in / 91.44 cm). Click a preset to populate both fields.

The Formulae

The conversion rests on one exact definition:

1 international inch = 0.0254 m = 2.54 cm   (exact, 1959 agreement)
1 foot               = 12 inches            (12 × 2.54 = 30.48 cm exact)
1 yard               = 36 inches            (36 × 2.54 = 91.44 cm exact)
1 mile               = 63,360 inches        (1,609.344 m exact)
1 metre              = 100 cm = 39.3700787401… inches (100/2.54, repeating)

To go from inches to centimetres:

cm = inches × 2.54

To go from centimetres to inches:

in = cm / 2.54
   = cm × 0.3937007874015748… (repeating)

The reverse factor is a repeating decimal, so for high-precision work always divide by 2.54 rather than multiply by 0.3937 (which truncates the seventh decimal place).

For paper sizes:

Worked Examples

Example 1, 1 inch:

• cm = 1 × 2.54 = 2.54 cm (exact)
• mm = 25.4 mm
• ft = 1/12 = 0.0833 ft (repeating)

Example 2, 12 inches (1 foot):

• cm = 12 × 2.54 = 30.48 cm (exact)
• m = 0.3048 m

Example 3, 36 inches (1 yard):

• cm = 36 × 2.54 = 91.44 cm (exact)

Example 4, 100 inches (8 ft 4 in, common TV size):

• cm = 100 × 2.54 = 254 cm
• m = 2.54 m

Example 5, 1 centimetre:

• in = 1 / 2.54 = 0.3937007874… in ≈ 0.3937 in
• mm = 10 mm

Example 6, 10 cm (a common phone-screen width):

• in = 10 / 2.54 = 3.9370078740… in ≈ 3.937 in

Example 7, 50 cm (≈ half a metre):

• in = 50 / 2.54 = 19.6850393701… in ≈ 19.685 in
• mm = 500 mm

Example 8, 0 inches (edge case):

• cm = 0; mm = 0; m = 0

Example 9, 72 inches (6 ft, common doorway height):

• cm = 72 × 2.54 = 182.88 cm
• m = 1.8288 m

Example 10, 1 metre (100 cm):

• in = 100 / 2.54 = 39.3700787401… in ≈ 39.370 in
• ft = 3.28084 ft

Where It Shows Up

• Screen and display sizes, TV, monitor, laptop, tablet and phone screens are universally measured on the diagonal in inches (a "24-inch monitor" means the diagonal is 24 inches = 60.96 cm). The diagonal is the only published dimension, the actual viewing area depends on the aspect ratio.
• Paper sizes, US Letter (8.5 × 11 in) is the US/Canada/Mexico standard; A4 (210 × 297 mm = 8.27 × 11.69 in) is the international ISO 216 standard used in the UK, Europe, Asia, Africa, South America and most of the world. Converting between the two is essential for international document exchange.
• Body measurements, clothing sizes (waist, chest, inseam) are often in inches in the US and centimetres elsewhere. A 32-inch waist is 81.28 cm.
• Construction and carpentry, US lumber is measured in inches and feet (a "2×4" is actually 1.5 × 3.5 inches, but the nominal 2 × 4 dimensions are 2 × 4 in = 5.08 × 10.16 cm). Metric construction uses millimetres and metres.
• Engineering drawings and CAD, international engineering practice often uses both inches and millimetres. Tolerance specifications can be in either unit; converting correctly is essential.
• Photography and print, sensor sizes, focal lengths, paper dimensions and print sizes can be in inches (8 × 10 print), centimetres (20 × 25 cm print) or millimetres.
• Bicycle wheel sizes, bicycle tyres are measured in inches (26", 27.5", 29" mountain; 700c road) or millimetres (700c = 622 mm BSD). The inch-based and metric systems coexist; converting between them matters when buying tyres internationally.
• Crafting, sewing and DIY, fabric widths, ribbon dimensions, pipe sizes and many other small measurements use inches in the US and cm elsewhere.

Common Mistakes

1. Confusing the international inch (25.4 mm) with the older US "survey inch", the survey inch was 25.4000508 mm (1/0.03937 m). It was used in some US land surveys before 1959 and creates a small discrepancy (~2 ppm) when comparing pre- and post-1959 data. This converter uses the international inch.
2. Rounding 2.54 to 2.5, the exact factor is 2.54 cm/in. Using 2.5 introduces 1.6% error, which is significant for precision work. This converter uses the exact factor.
3. Multiplying cm by 0.3937 instead of dividing by 2.54, when going cm → in, dividing by 2.54 is exact; multiplying by 0.3937 truncates the seventh decimal place. For most uses this is fine, but for surveying or precision engineering it accumulates.
4. Using a "diagonal inch" thinking for non-rectangular shapes, an "inch" is a unit of length, not area. A "32-inch TV" is the diagonal length, not the width, height or area. Don't try to use this converter for area or volume.
5. Confusing inches with "lines" (old typographic unit), the "line" was 1/12 inch in old typography and 1/6 inch in some French traditions. Modern typography uses points (1/72 inch or 0.353 mm). This converter is for inches only.
6. Treating the inch as ambiguous between systems, the international inch (25.4 mm) is now universal, but the historical differences between the English inch, US inch and continental inch existed. Modern statute and convention use the international inch only.
7. Computing screen size incorrectly, a "24-inch monitor" has a 24-inch diagonal. For a 16:9 aspect ratio, the width is about 20.9 in (53.13 cm) and the height is about 11.8 in (29.95 cm), NOT 24 × 13.5 in.
8. Forgetting the inch in sewing/needlework, needle sizes in the US use a different numbering system (the larger the number, the smaller the needle); the UK system uses actual mm. Convert between US and metric needle sizes via a needle-size chart, not directly via inch-to-cm.

Frequently Asked Questions

How many centimetres are in an inch? One international inch = exactly 2.54 cm, by the international yard-and-pound agreement of 1 July 1959 (which fixed the yard at 0.9144 m exactly, making the inch = 1/36 yard = 0.9144/36 = 0.0254 m = 2.54 cm exactly). This is the only definition used in modern science, engineering, trade and daily life.

How many inches are in a centimetre? One centimetre = 1/2.54 = 0.3937007874015748… inches (repeating decimal). For most applications, 0.3937 in is sufficient precision; for engineering, divide by 2.54 to get the full repeating-decimal value.

Is 2.54 cm/inch exact or rounded? Exact. The international agreement of 1 July 1959 fixed the inch at 0.0254 m exactly (and therefore at 2.54 cm exactly). There is no rounding in the definition. The metre itself was redefined in 1983 via the speed of light, which kept the inch at the same value.

What's the difference between the international inch and the survey inch? The international inch (25.4 mm exactly) has been the standard in science, engineering and most trade since 1 July 1959. The US "survey inch" (25.4000508 mm exactly) was used in some pre-1959 US land surveys; the difference is ~2 parts per million. This converter uses the international inch, which is universal in modern contexts.

What's the size of a 24-inch monitor in centimetres? A 24-inch monitor has a 24-inch (60.96 cm) diagonal. For a 16:9 aspect ratio, the width is about 20.92 in (53.13 cm) and the height is about 11.77 in (29.89 cm). For a 16:10 aspect ratio, the width is 20.35 in (51.69 cm) and the height is 12.72 in (32.30 cm).

How many inches is a 6 ft tall person? 6 ft = 6 × 12 = 72 inches = 72 × 2.54 = 182.88 cm = 1.8288 m. The reverse: a 1.83 m person is about 72 inches or 6 ft.

How many centimetres is A4 paper? A4 paper (ISO 216 standard) is 210 × 297 mm = 21.0 × 29.7 cm = 8.27 × 11.69 in. The aspect ratio is √2 ≈ 1.4142 (a defining feature of the ISO A series).

How many inches is US Letter paper? US Letter (ANSI/ASME Y14.1) is 8.5 × 11.0 in = 21.59 × 27.94 cm = 215.9 × 279.4 mm. The aspect ratio is 11/8.5 ≈ 1.294 (not the √2 of ISO paper), which is why A4 doesn't fit perfectly in a US Letter print area.

What is the smallest unit smaller than an inch? The inch is divided into fractions in customary US practice (½, ¼, ⅛, 1/16, 1/32, 1/64 in) and into thousandths (called "thou" or "mil") for engineering. 1 thou = 0.001 in = 0.0254 mm. The inch is also divided into 12 lines (1 line = 1/12 in ≈ 2.117 mm) in some traditional contexts, but this is rare in modern use.

Can I use this converter for sewing measurements? Yes, body measurements (waist, chest, inseam, hip) and fabric dimensions convert directly. Note that clothing sizes in different countries use different conventions (US/UK sizes 4, 6, 8, … vs European 36, 38, 40, …), this converter handles the unit conversion only, not the size-system mapping.

Is this calculator suitable for professional or commercial use? yes, the Inches to Centimeters Converter, 1 in = 2.54 cm Exact provides mathematically correct results that are suitable for professional, commercial, and educational use. For high-stakes applications (legal land descriptions, surveying, engineering tolerances), verify results with a domain expert. The formulas used are well-established and validated against reference standards from NIST and the BIPM.

For the Inches to Centimeters Converter, 1 in = 2.54 cm Exact, How often are the underlying formulas updated? For the Inches to Centimeters Converter, 1 in = 2.54 cm Exact, the Inches to Centimeters Converter, 1 in = 2.54 cm Exact formulas are based on established scientific, mathematical, or industry-standard references and rarely require updates. When standards change (e.g., the 1983 redefinition of the metre via the speed of light), this calculator is updated to reflect the current authoritative source. For the Inches to Centimeters Converter, 1 in = 2.54 cm Exact, For the Inches to Centimeters Converter, 1 in = 2.54 cm Exact, Each calculator's references section lists the specific sources used.

References

1. International yard-and-pound agreement of 1 July 1959 among the US, UK, Canada, Australia, New Zealand and South Africa, fixed 1 yard = 0.9144 m exactly (and therefore 1 inch = 0.0254 m exactly). Federal Register, US National Archives.
2. UK Weights and Measures Act 1985 (c. 72), Schedule 1, confirms the inch as 0.0254 m. The Stationery Office, London.
3. For the Inches to Centimeters Converter, 1 in = 2.54 cm Exact, NIST Special Publication 811 (2008), Appendix B.6, Recommended conversion factors for length, including the exact 1 in = 0.0254 m factor. For the Inches to Centimeters Converter, 1 in = 2.54 cm Exact, National Institute of Standards and Technology.
4. For the Inches to Centimeters Converter, 1 in = 2.54 cm Exact, BIPM SI Brochure (9th edition, 2019), §2.3.1, defines the metre via the speed of light since 1983. Bureau International des Poids et Mesures.
5. ISO 216:2007, defines the international A series paper sizes (A4 = 210 × 297 mm, aspect ratio √2). International Organization for Standardization.
6. ANSI/ASME Y14.1-2012, defines US Letter (8.5 × 11 in) and US Legal (8.5 × 14 in) paper sizes. American National Standards Institute.
7. Taylor, B. N. and Thompson, A. (eds.), NIST Special Publication 811 (2008 edition), the canonical US reference for unit conversions.

Also try these free tools:

• Centimeters to Inches Converter, same factor, opposite direction
• Inches to Feet Converter, for shorter imperial/imperial conversions
• Yards to Feet Converter, for longer imperial/imperial conversions
• Paper Size Converter, for A-series, US Letter and other standard sizes