Screen size converter
Screens are sold by the diagonal, but a wall needs the width. Pick the shape and this gives you both.
That's about the same as a living room TV. That is about 121.8 cm wide and 68.49 cm tall.
What it means
How big is that screen?
Diagonals are of the picture itself. Bezels and stands add to the space a screen actually needs.
Every unit
Your screen in every measurement
Learn
Three things worth knowing
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A 16:9 screen is 87% diagonal wide
Multiply the diagonal by 0.87 for the width and 0.49 for the height. A 55-inch TV is 122 cm wide and 68 cm tall.
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Why the diagonal at all
Early television tubes were round, and the diagonal was the only honest way to state how much picture you got. The habit survived the shape.
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Same diagonal, less picture
A 21:9 ultrawide has noticeably less area than a 16:9 screen of the same diagonal. Stretching the shape shrinks the picture.
Shortcuts
Popular screen size conversions
Background
About screen sizes
A diagonal alone does not describe a screen: a 27-inch 16:9 monitor is 60 cm wide, while a 27-inch 4:3 one is 55 cm. For a ratio w:h, width = diagonal × w ÷ √(w² + h²).