Screen Size Calculator

Work out a display's physical width, height, viewable area, and pixel density (PPI) from its diagonal size, aspect ratio, and pixel resolution.

Quick Facts

Method
Pythagorean theorem: diagonal² = width² + height²
PPI = sqrt(horizontal px² + vertical px²) ÷ diagonal size in inches.

Your Results

Calculated
Width × height (inches)
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Physical display dimensions
Width × height (cm)
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Metric equivalent
Viewable area
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Total screen area
Pixel density
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Pixels per inch (PPI)

Ready

Set the diagonal size, aspect ratio, and resolution, then press Calculate.

How the Screen Size Calculator Works

A screen's advertised "size" is its diagonal measurement — the straight-line distance from one corner of the visible display to the opposite corner, excluding the bezel. That single number does not fix the width and height on its own; it takes the diagonal together with the aspect ratio (the proportion of width to height) to pin down the actual dimensions. This calculator uses the Pythagorean theorem, the same relationship that governs any right triangle, to recover width, height, area, and pixel density from those inputs.

The formulas

Given a diagonal D and an aspect ratio expressed as width:height (for example 16:9, so ratio r = 16/9 ≈ 1.778):

  • Height: the screen's width, height, and diagonal form a right triangle, so D² = width² + height². Since width = r × height, this simplifies to height = D / √(r² + 1).
  • Width: once height is known, width = r × height.
  • Area: simply width × height, reported in both square inches and square centimeters (1 inch = 2.54 cm).
  • Pixel density (PPI): the number of pixels packed into each inch of diagonal, PPI = √(horizontal px² + vertical px²) / D. This uses the same Pythagorean relationship applied to the pixel grid instead of the physical dimensions.

Common aspect ratios

  • 16:9 — standard widescreen for HD/4K TVs, most monitors, YouTube, and streaming video
  • 16:10 — common on laptops and some professional monitors; slightly taller than 16:9
  • 4:3 — older TVs and monitors, and some tablets like the iPad
  • 21:9 and 32:9 — ultrawide and super-ultrawide monitors used for productivity and cinematic gaming
  • 1:1 — square format, occasionally used for specialty displays
  • 9:16 — vertical/portrait orientation, the mobile-phone default

Why diagonal size alone does not tell the whole story

Two screens with the identical diagonal measurement can have noticeably different width, height, and area if their aspect ratios differ. A 34-inch 21:9 ultrawide monitor is much wider and shorter than a 34-inch 16:9 monitor would be, and the two have different total viewable area even though "34 inches" sounds like the same size. Comparing screens fairly means checking width, height, and area — not just the diagonal number on the box.

Frequently Asked Questions

How is screen size measured?
Screen size is the diagonal distance across the visible display area, corner to corner, not including the bezel. Given that diagonal and the aspect ratio (width to height), the Pythagorean theorem (diagonal squared equals width squared plus height squared) yields the actual width and height.
What is PPI and why does it matter?
Pixels per inch (PPI) measures pixel density: PPI equals the square root of (horizontal pixels squared plus vertical pixels squared), divided by the diagonal size in inches. Higher PPI means finer, sharper detail at a given viewing distance; roughly 220 PPI or higher is often called Retina-class sharpness.
Does a larger diagonal always mean more screen area?
Not necessarily. Screen area depends on both diagonal size and aspect ratio. A 27-inch 21:9 ultrawide has a different width, height, and total area than a 27-inch 16:9 monitor, because the two shapes divide the same diagonal differently.
How do I find my aspect ratio if I only know the resolution?
Divide the horizontal resolution by the vertical resolution. For example, 1920 divided by 1080 equals 1.778, which matches 16:9 (16 divided by 9 is also 1.778). Compare that decimal value to common ratios like 16:10 (1.6), 4:3 (1.333), or 21:9 (2.333) to identify the closest match.

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