Why TVs and monitors are still sized in inches, everywhere

Walk into an electronics store in Berlin, Tokyo, or São Paulo — all fully metric markets — and the television specs will still read "55 inch" or "65 inch," not centimeters. It's one of the few places the inch survives as a genuinely global, non-US convention, and the number itself measures something less obvious than most people assume: a corner-to- corner diagonal, not the screen's width.

Diagonal, not width — and why that matters

A screen's advertised size is always the diagonal measurement of the visible display area, a convention that predates flat panels and goes back to the circular face of early cathode- ray tubes, where diagonal was the only dimension that stayed consistent regardless of how the tube was mounted. The habit carried over to flat rectangular screens even though width and height would now be just as easy to state. Because a diagonal is always longer than either side of a rectangle, a "55-inch" screen is narrower than 55 inches in actual width — for a standard 16:9 panel, about 47.9 inches (121.7 cm) wide and 27 inches (68.5 cm) tall.

These figures come from splitting the diagonal using the Pythagorean relationship for a 16:9 rectangle: width = diagonal × 0.8720, height = diagonal × 0.4902. A different aspect ratio — an ultrawide monitor at 21:9, say — divides the same diagonal into a proportionally wider, shorter rectangle, so two screens with an identical advertised size can look quite different side by side. Our aspect ratio calculator handles that split for any ratio, not just 16:9.

Why the inch survived here specifically

Most consumer goods sold in metric countries are specified in metric units — cars in kilometers per hour, food in grams, height in centimeters. Screens are the exception because the display and television industry became genuinely global early, with American, Japanese, and (later) Korean and Chinese manufacturers all marketing into a US-anchored market where inches were already the norm. Once "40-inch," "55-inch," and "65-inch" became recognizable shorthand for a product tier — the way "megapixels" or "gigabytes" became shorthand elsewhere — retailers everywhere kept using it rather than fragmenting the market with a parallel centimeter-based naming scheme. It's a case where an inherited unit won out over a legally mandated one purely because of standardization and consumer recognition, not regulation. The same phenomenon shows up in photography (film and sensor formats), paper sizes in a few contexts, and computer monitor diagonals, which follow the identical inch-and-diagonal convention as TVs.

Converting your own screen measurement

If you're measuring a physical screen with a tape measure — to check it'll fit a cabinet or wall mount, for instance — measure the diagonal of the visible glass, corner to corner, not the outer bezel. Convert that number between inches and centimeters with the exact 2.54 factor (1 inch = 2.54 cm) rather than the industry's rounded marketing figures, since real panels often measure a few millimeters off their advertised class size. For width and height instead of diagonal, apply the aspect-ratio split shown above once you know the panel's ratio, which is usually printed in the product spec sheet alongside the diagonal.