Screen Dimensions from Diagonal

Turn a screen diagonal into the width and height that decide whether it fits.

What you provide

Screen diagonal(in)

The number the display is sold by — 27", 34", 55".

Aspect ratio

16:9 for most monitors and TVs, 21:9 or 32:9 for ultrawides, 16:10 for many laptops, 4:3 for older panels.

Result

23.5 × 13.2 in

A 27-inch 16:9 panel measures 23.5 by 13.2 inches of active area — 59.8 cm by 33.6 cm. Add bezel and a stand before comparing that against the space you have.

Diagnostic telemetry

Panel width59.8 cm: 23.5 in
Panel height33.6 cm: 13.2 in
Viewable area2010 cm²: 312 in²
Aspect ratio: 16:9

What this cannot tell you

Gives the active panel area only. The monitor itself is larger — bezels add roughly a quarter to half an inch per side on a modern display, and the stand adds depth and height beyond that. Measure the chassis, not this, before committing to a shelf or a desk cutout.
Assumes the advertised diagonal is exact. Manufacturers round: a panel sold as 27 inches is often 27.0 in one range and 26.9 in another, and televisions are frequently rounded to the nearest inch.
Says nothing about whether the picture is good. Size, panel type, refresh rate and colour accuracy are independent of each other.

Take this with you

How this calculation works

A diagonal and an aspect ratio fully determine a rectangle, so the width and height come straight out of Pythagoras: the diagonal is the hypotenuse of a triangle whose sides are in the ratio you enter. The calculator solves that, converts to centimetres, and — when the ratio is not 16:9 — compares the result against a 16:9 panel of the same diagonal. That comparison is the useful part, because 16:9 is the shape almost everyone already has on their desk and can picture, and a diagonal on its own is the one specification that does not tell you whether something fits.

What the results mean

Panel width and height: The active picture area, corner to corner. The physical monitor is bigger by its bezel on every side.
Viewable area: Width times height. This is what actually grows or shrinks when you change shape at a fixed diagonal, and it moves in ways the diagonal hides.
Against the same diagonal in 16:9: How much wider and shorter this shape is than the familiar one. A 34-inch 21:9 is 1.6 inches wider and 3.3 inches shorter than a 34-inch 16:9 would be, with 15% less area.

Common problems and fixes

The monitor did not fit even though the width matched: You measured the panel, not the product. Bezels and the stand's footprint are not in this figure. Manufacturers publish chassis dimensions with and without the stand — use those for clearances.
My new bigger monitor looks shorter than the old one: That is the expected result of moving from 16:9 to 21:9. At the same diagonal an ultrawide trades height for width: a 34-inch 21:9 is 3.3 inches shorter than a 34-inch 16:9. Against a 27-inch 16:9 it is barely taller at all — 13.4 inches against 13.2 — so all seven inches of extra diagonal went sideways.
I do not know my aspect ratio: Divide the horizontal resolution by the vertical. 2560×1440 and 3840×2160 are 16:9; 3440×1440 is 21:9; 1920×1200 is 16:10; 5120×1440 is 32:9.

Frequently asked questions

Why is a 34-inch ultrawide shorter than a 27-inch 16:9?

Because the diagonal is shared between width and height according to the shape. A 21:9 panel puts far more of that diagonal into width, so the height comes down. A 34-inch 21:9 measures 31.3 by 13.4 inches; a 27-inch 16:9 measures 23.5 by 13.2. The ultrawide is 7.7 inches wider and essentially the same height, despite seven inches more diagonal.

Does a bigger diagonal always mean more screen area?

No. Area depends on shape as well as diagonal. A 32:9 panel at a given diagonal has noticeably less area than a 16:9 one at the same diagonal, because the rectangle is far from square and area falls as a rectangle gets more elongated.

Should I use this to check a wall mount?

Only as a starting point. Mounting depends on the chassis size and the VESA hole pattern, neither of which follows from the panel dimensions. Take both from the manufacturer's spec sheet.

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