Screen Size Calculator

Diagonal to width and height

The hypotenuse of the ratio triangle is √(16²+9²). Scale that to 27 inches. Centimetres are inches × 2.54.

If you also type a resolution, PPI = √(W²+H²) / diagonal. That is the same formula as the PPI page, kept here so a monitor shopper sees both numbers.

Worked screen examples

27″ 16:9 → 23.53 × 13.24 in. 2560×1440 @ 27″ → ≈ 108.8 PPI. Both are fixtures.

Common mistakes

Using the box diagonal that includes bezel marketing. Use the viewable spec.

Mixing 21:9 marketing with a 43:18 panel when computing width.

The 27 inch 16:9 fixture

Width = 27 × 16 / √(16²+9²) ≈ 23.53 in. Height ≈ 13.24 in. Centimetres are those inches times 2.54. If you then type 2560×1440, PPI is √(2560²+1440²)/27 ≈ 108.8. Both numbers are fixtures shared with the PPI page so the two tools cannot drift.

A 27 inch 16:10 panel is a different width. Change the ratio chip before you trust the centimetre readout.

Use the screen size calculator when the box only prints a diagonal. Pick the real ratio of the glass, read the width and height in inches and centimetres, and only then decide whether the panel fits the desk. A 21:9 nickname is not the same triangle as 3440×1440, so the width will be short if you leave the chip on the marketing name.

Viewable diagonal only

Box art that says 27 inch including a soundbar is not the viewable spec. The formula uses the hypotenuse of the ratio triangle scaled to that diagonal. 27″ 16:9 → about 23.53 × 13.24 in. Add 2560×1440 and PPI is about 108.8.

Ultrawide shoppers should pick the real panel ratio (64:27 or 43:18) rather than the 21:9 chip, or the computed width will be slightly short of the glass.

Frequently asked questions