Inches to cm Converter

1 inch = 2.54 cm exactly. 6 in ≈ 15.24 cm (a US dollar bill is about 6.14 in / 15.6 cm long).

TV screens — 32" ≈ 81 cm diagonal, 43" ≈ 109 cm, 55" ≈ 140 cm, 65" ≈ 165 cm, 75" ≈ 191 cm.

Height — 5' 0" = 152.4 cm, 5' 6" = 167.6 cm, 5' 10" = 177.8 cm, 6' 0" = 182.9 cm, 6' 4" = 193.0 cm.

Furniture — 24 in desk depth = 61 cm; 30 in desk height = 76 cm; 72 in sofa = 183 cm.

Paper — US Letter (8.5 × 11 in) = 21.59 × 27.94 cm; A4 (the metric standard) = 21.0 × 29.7 cm — close, but the slightly different proportions are why US documents do not always print cleanly on European printers.

Before 1959 the US inch and the UK (Imperial) inch differed by a few millionths of a meter. The US used the 1893 Mendenhall Order definition (1 m = 39.37 in exactly, making 1 in ≈ 2.540005 cm). The UK used a slightly different value based on the Imperial Standard Yard.

The 1959 International Yard and Pound Agreement, signed by the US, UK, Canada, Australia, New Zealand, and South Africa, redefined the inch as exactly 25.4 millimeters. This eliminated the discrepancy and tied the inch to the metric system through a clean conversion factor. The US Survey Foot kept the old definition for legacy land surveys until 2023, when NIST officially retired it in favor of the international foot.

Multiply inches by 2.5 and add about 2%. Close enough for everyday conversions and easier than reaching for a phone.

Or: double the inches and add a quarter (×2.25). Less accurate but very fast.

Going the other way (cm to inches): divide by 2.54, or multiply by 0.3937. 180 cm ÷ 2.54 ≈ 70.87 in ≈ 5 ft 10.87 in.

For very small lengths, work in millimeters: 1 in = 25.4 mm exactly. Engineering drawings in the US sometimes call out dimensions in thousandths of an inch ('mils'); 1 mil = 0.0254 mm = 25.4 micrometers.

For interior design, clothing, and most consumer purchases, conversions to the nearest centimeter (or quarter-inch) are plenty. The width of a sofa specified as 84 inches converts to 213.36 cm, but the showroom and the apartment door frame are not measured to that precision anyway.

For machining, woodworking, and printing, the millimeter is the natural unit. A 1/32-inch dado in a cabinet panel is 0.79 mm — small enough that the difference between 0.79 mm and 0.80 mm is invisible, but a full millimeter of error produces a sloppy joint.

For pharmacy, lab, and scientific work, never improvise the conversion. Use a calibrated rule or NIST-traceable digital caliper. The 2.54 cm definition is exact, so the conversion itself introduces no error — but reading a tape measure to within 0.5 mm is genuinely hard without proper tools.

A useful sanity check: 1 cm is roughly the width of a fingernail; 1 inch is roughly the width of a thumb at the knuckle. If a converted dimension defies that mental check by more than a factor of two, you probably mixed up which direction the conversion went.

US shop drawings, tape measures, and hardware sizes use binary fractions of an inch rather than decimals, which makes conversion to millimeters a two-step job: turn the fraction into a decimal, then multiply by 25.4. Because every fraction is a power of two, the millimeter results are exact rather than repeating decimals.

1/32 in = 0.79 mm · 1/16 in = 1.5875 mm · 1/8 in = 3.175 mm · 3/16 in = 4.7625 mm · 1/4 in = 6.35 mm · 5/16 in = 7.9375 mm · 3/8 in = 9.525 mm · 1/2 in = 12.7 mm · 5/8 in = 15.875 mm · 3/4 in = 19.05 mm · 7/8 in = 22.225 mm · 1 in = 25.4 mm.

This table explains a frustration familiar to anyone with a mixed toolbox: metric and imperial fasteners are close enough to fool you but never actually interchangeable. A 13 mm socket measures 0.512 in while a 1/2 in socket is 12.7 mm — a 0.3 mm gap that will round over the corners of a bolt head if you force it. The same is true of 10 mm versus 3/8 in (9.525 mm) and 19 mm versus 3/4 in (19.05 mm), which is the one pair close enough to genuinely substitute in a pinch.

For drill bits the gap matters more. A 1/4 in bit cuts a 6.35 mm hole; if a plan calls for a 6 mm hole to tap M6 threads, the imperial bit removes too much material and the threads will strip. Match the bit to the standard the drawing was written in.

Even in countries that metricated decades ago, a handful of product categories are still specified in inches because the manufacturing standards are global and were set in inch-based factories. Knowing which ones saves confusion when shopping internationally.

Screens — TVs, monitors, laptops, tablets, and phones are all sold by diagonal inches worldwide. Plumbing — pipe and fitting sizes (1/2 in, 3/4 in, 1 in) are nominal inch designations, and the actual outside diameter does not match the label. Tires — the final number in a size like 225/45R17 is the wheel diameter in inches, even on a car sold in Paris.

Also inch-based: bicycle wheels (26 in, 27.5 in, 700c is the odd metric exception), rack-mounted equipment (the 19 in rack and its 1.75 in 'U' height), vinyl records (7, 10, and 12 in), fire hose and camera filter threads, and shipping-container internal dimensions. Lumber is a special case — a US '2×4' is neither 2 nor 4 inches, having been planed down from rough-sawn stock to an actual 1.5 × 3.5 in (38 × 89 mm).

The practical rule when ordering across borders: if the category appears on this list, the inch number is the real specification and any centimeter figure in the listing is a converted courtesy. Everywhere else — clothing, furniture dimensions, construction drawings — the metric figure is authoritative and the inch value is the conversion.