Inches to Centimeters Converter

centimeters = inches × 2.54

Example: 10 in × 2.54 = 25.4 cm. To convert back, multiply cm by 0.3937.

The inch-to-centimeter conversion (exactly 2.54 since 1959) is the most-used small-measurement bridge in daily life: screen sizes (a 65-inch TV is a 165 cm diagonal), waist sizes, phone dimensions, and photos for passports. It is also the backbone for converting body height from imperial to metric.

Television and monitor sizes are measured diagonally in inches even in fully metric countries, which is why a 65-inch TV is sold as '65-inch' in Berlin and Tokyo too. The diagonal in centimeters — 165.1 for that 65-inch set — appears on the energy label but never in the marketing. Phone screens follow the same convention: a '6.7-inch display' is a 17 cm diagonal, though phone spec sheets elsewhere in the world quietly list millimeters.

The inch has been exactly 2.54 cm since 1959, when the US, UK, Canada, Australia, New Zealand, and South Africa agreed on a common definition. Before that, the US inch and the imperial inch differed by a few parts per million — a rounding error for carpenters, but enough to matter for precision machining, which is why the agreement happened at all.

A standard imperial ruler divides each inch into 16 equal parts, so the smallest mark is 1/16 of an inch. Converting that to metric gives exactly 1.5875 mm — a number that almost never appears on any product label but that carpenters and machinists encounter constantly when they work across both systems. The fractions on a tape measure follow a predictable pattern: 1/2 inch is 12.7 mm, 1/4 inch is 6.35 mm, 1/8 inch is 3.175 mm, and 1/16 inch is 1.5875 mm. Each step halves the previous value, which is why the marks on a physical ruler get shorter as the denominator doubles — the longest mark is the half-inch, then quarter-inch marks are slightly shorter, and so on down to 1/16 at the smallest.

Furniture assembly instructions from US brands routinely specify pilot-hole diameters in fractions of an inch: a 3/16-inch bit (4.7625 mm) is common for wood screws, and a 5/16-inch bit (7.9375 mm) suits larger bolts. European drill bits are sold in 0.5 mm increments, so you typically round to the nearest available metric size and verify by test-fitting. The rounding margin is rarely more than 0.2 mm, which matters for structural fasteners but not for shelf pins. Carrying a printed reference card or using /cm-to-inches on your phone while shopping at a hardware store saves time — mental division of arbitrary fractions by 2.54 is not fast.

Spec sheets for imported cabinetry, flooring, and countertop materials often mix units within the same document: overall width in inches, panel thickness in millimeters, and weight in kilograms. Reading them accurately requires converting only the dimensions that affect your cuts. A countertop listed as 96 inches wide with a 19 mm edge profile means you plan for 243.84 cm of linear run and a 1.9 cm overhang on both sides. Treating the two units separately — rather than converting everything to one system first — reduces the chance of a compounding rounding error that costs you a second trip to the timber yard.

Height is one of the most common reasons people need to convert inches to centimeters. In the United States, the United Kingdom, and a handful of other countries, height is given in feet and inches: 5 feet 9 inches, for example, is (5 × 12 + 9) × 2.54 = 69 × 2.54 = 175.26 cm. The decimal is not a rounding curiosity — it reflects the fact that 175 cm and 176 cm are both in common use as self-reported heights, and the actual value sits between them. Medical records in hospitals across the US document height in both units, but the number that gets entered into drug-dosing software is almost always the centimeter figure, so the conversion needs to be exact rather than rounded to the nearest whole number.

Clothing size tables translate height and chest or waist measurements from inches to centimeters with a direct 2.54 multiplier, but the resulting numbers rarely match the labeled garment sizes, which have their own grading logic. A US men's size 40 jacket corresponds roughly to a 101.6 cm chest, but a German size 50 in the same style might be cut to 100 cm — close enough to try on, far enough to matter for a tailored fit. Shoe sizing is even further removed from the underlying foot length: a US men's size 10 corresponds to a foot length of approximately 28 cm, which maps to European size 44 and UK size 9.5, but the exact correspondence depends on the brand's last. Checking the brand's own conversion table rather than a generic chart avoids the half-size gaps that cause returns.

In custom and bespoke clothing, 0.5 cm is the standard tolerance that separates a passing fit from a failed one. A suit jacket sleeve adjusted by 1 cm (about 3/8 inch) is visible to the eye in a fitting; half that amount changes how the jacket sits at the shoulder. Alterations tailors working in inches charge by 1/4-inch increments precisely because the metric equivalent — 0.635 cm — is awkward to mark on an inch-calibrated tape measure. If you are communicating measurements to a maker overseas, always specify in centimeters and include the tolerance explicitly, because the assumption of plus-or-minus 1 cm is not universal across workrooms.

Television and monitor diagonal sizes are sold in inches worldwide, even in countries that otherwise use the metric system exclusively. A 55-inch television has a diagonal of exactly 139.7 cm (55 × 2.54), and a 65-inch model measures 165.1 cm. The width and height of the screen depend on the aspect ratio: for a 16:9 display, a 55-inch diagonal gives approximately 121.5 cm wide by 68.4 cm tall. These numbers matter when planning wall mounts or IKEA TV units, which list internal dimensions in millimeters, meaning you need the metric equivalent of the diagonal before you can calculate whether the panel will overhang the stand.

Paper is another case where the two systems coexist without ever converging. ISO A4, used throughout Europe, Asia, and most of the world, measures 210 × 297 mm. US Letter is 8.5 × 11 inches, which is 215.9 × 279.4 mm — about 6 mm wider and 18 mm shorter. The difference is real enough that a document formatted for one size will have visible margin differences when printed on the other, and PDF margins set to exact inch values do not correspond to any round millimeter measurement. When preparing print files for international distribution, setting the document to A4 first and converting layout measurements explicitly avoids the margin-shift complaints that follow automatic paper-size rescaling.

Dimensional lumber sold in the United States carries nominal names that have not reflected actual dimensions for decades. A 2×4 stud measures 1.5 inches by 3.5 inches, which is 3.81 cm by 8.89 cm. A 2×6 is 1.5 by 5.5 inches, or 3.81 by 13.97 cm. The gap between the name and reality exists because lumber shrinks during drying and then gets surfaced smooth on all four sides, which removes additional material. European construction timber is sold by actual metric dimensions — a 47 × 100 mm stud is exactly that — which means a US framing plan converted to metric requires substituting the real dimensions, not the nominal ones. For anyone working across both systems on a renovation, the /feet-to-cm page covers longer measurements, but the actual cross-section of the lumber always needs its own 2.54-based conversion.

The exact conversion factor is 2.54 centimeters per inch, fixed since the International Yard and Pound Agreement of 1959. For mental arithmetic, a useful approximation is: multiply the inch value by 2.5, then add 1.6 percent of the original. For small numbers the 1.6 percent correction is negligible — 6 inches times 2.5 equals 15.0 cm, and the exact answer is 15.24 cm, a difference of 2.4 mm. For larger measurements the error accumulates: 36 inches times 2.5 gives 90.0 cm, but the exact value is 91.44 cm, off by 1.44 cm. Whether that gap matters depends on context.

A handful of anchor points cover most everyday conversions without any arithmetic. One inch equals 2.54 cm exactly. Six inches (half a foot) equals 15.24 cm. Twelve inches (one foot) equals 30.48 cm. Thirty-six inches (one yard) equals 91.44 cm. One hundred inches equals 254 cm exactly — a consequence of the 2.54 definition that makes round metric numbers correspond to awkward inch values and vice versa. Memorizing these anchors lets you bracket any measurement: 20 inches is between 12 (30.48 cm) and 36 (91.44 cm), so you know the answer is somewhere in the low-to-mid 50s before you calculate the exact 50.8 cm.

The level of precision required depends on the domain. Engineering drawings and medical device specifications typically require four significant figures, and rounding 2.54 to 2.5 introduces a 1.6 percent error that is unacceptable for parts with tolerances measured in hundredths of a millimeter. Medical applications — bone screw lengths, catheter sizes, implant dimensions — are even less forgiving, and the conversion in those contexts should always be done by a verified tool rather than mental arithmetic. At the other extreme, choosing the length of a curtain rod or estimating whether a sofa will fit through a doorway tolerates 1 cm of error, making the 2.5 approximation entirely adequate. The question to ask before rounding is not how close the approximation is in percentage terms, but what physical consequence a 1 mm or 1 cm error has in your specific situation.