Inches to Cm Converter

inches to centimeters — quick reference

The formula, worked line by line

The inch is a metric unit wearing an old name. On 1 July 1959 the standards bodies of the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa signed the International Yard and Pound Agreement, fixing the yard at exactly 0.9144 meters. Divide by 3 and the foot is exactly 0.3048 meters; divide by 36 and the inch is exactly 0.0254 meters, which is 2.54 centimeters or 25.4 millimeters.

Two related conversions follow from the same constant but are not the same multiplier, which is the mistake worth guarding against: areas scale by 2.54 squared and volumes by 2.54 cubed.

centimeters = inches × 2.54
millimeters = inches × 25.4
from feet and inches: cm = (feet × 12 + inches) × 2.54
22 in → 22 × 2.54 = 55.88 cm

The multiply-by-2.5 shortcut drops the 0.04 from the factor, an error of about 1.6 percent, and it always reads low. The ladder below shows how far it drifts as the measurement grows.

What makes it worse than an equivalent overestimate is the direction: an undercount tells you the object is smaller than it is, so it passes a clearance check it should fail. If you are going to use a shortcut when something has to fit through an opening, use one that reads high, such as multiplying by 2.6, and treat the result as a worst case.

Squares, cubes and the survey foot

The trap that catches people is squaring and cubing. One inch is 2.54 cm, but one square inch is 2.54 squared, which is 6.4516 square centimeters, and one cubic inch is 2.54 cubed, which is 16.387064 cubic centimeters. So a 12 by 10 by 8 inch box is 30.48 by 25.4 by 20.32 cm on its edges, but its 960 cubic inches are 15,731.58 cubic centimeters, or 15.73 litres, not 960 times 2.54.

The other wrinkle worth knowing is historical: the United States kept a second, very slightly longer foot for land surveying, the US survey foot of 1200/3937 meters, until NIST and the National Geodetic Survey deprecated it on 31 December 2022. It differed by about two parts per million, roughly an eighth of an inch per mile, so it never mattered for a sofa and mattered a great deal for a coordinate grid.

How to use the inches to cm converter

When your measurement is in inches but the thing you are checking it against is metric, this is the conversion you want.

A flat-pack box that has to clear a doorway, a parcel measured against a courier limit written in centimeters, a clothing size chart from a European brand, a bracket you are matching to metric hardware, a drawing you are handing to a fabricator who works in millimeters: in each case the inch figure is what you measured and the metric figure is what gets checked.

Enter the inches and read the centimeters, or press Swap to run it the other way. The multiplier is exactly 2.54, so the answer is not an approximation and can be relied on down to the millimeter.

The doorway and furniture case is the one that saves a wasted delivery. A sofa listed at 36 inches deep is 91.44 cm, and if the turn in your hallway measures 90 cm that is the difference between it fits and it goes back on the truck. A 30 by 80 inch door opening is 76.2 by 203.2 cm, and the checklist below is the discipline that keeps a delivery from bouncing.

• Convert every critical dimension: width, depth and height, not just the obvious one
• Convert the diagonal of the largest face, because the diagonal is what actually has to pass through a doorway when the piece is tipped
• Measure the narrowest point of the whole route, since a hallway turn is often tighter than the door it leads to
• Keep a margin of a centimeter or two beyond the converted figure for handles, feet and the angle you will carry it at

For a fast estimate, multiply the inches by 2.5. It undershoots the true 2.54 by about 1.6 percent, so 22 inches comes out as 55 cm against a true 55.88, and 60 inches comes out as 150 cm against a true 152.4, an error of nearly an inch.

If you want a better mental version, multiply by 2.5 and then add one and a half percent, or remember that ten inches is 25.4 cm and scale from there. For any real clearance, cut, mount or shipping check, use the exact factor and then add margin on purpose rather than by accident.

Why do parcel and cabin-bag limits need exact centimeters?

Shipping limits abroad are written in centimeters, and often as a single combined figure rather than three separate ones, either length plus girth or the sum of the three dimensions. A box measured at 12 by 10 by 8 inches is 30.48 by 25.4 by 20.32 cm, and it is that metric set the carrier rules are tested against.

Convert each dimension exactly and then add, rather than converting the total, because rounding three numbers up and then summing them can invent several centimeters that are not there. The same discipline applies to airline cabin-bag sizers, which are physical boxes cut to metric dimensions: your bag either goes in or it does not, and a converted figure that reads short will tell you it fits when it does not.

Every inches value, worked out

65 common inches figures each get their own page, with the answer at full precision, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.

Questions people ask