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Monitor size, resolution and pixel density

Two monitors can share a resolution and look completely different. A 4K panel at 24 inches is dense and crisp; the same resolution stretched to 43 inches has the pixel density of a budget office screen. Pixel density, not resolution alone, determines whether text looks sharp at desk distance.

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How pixel density is worked out

Pixels per inch divides the pixel count along the diagonal by the diagonal in inches. For a 27-inch 3840 × 2160 panel, the diagonal pixel count is the square root of 3840² plus 2160², which is 4405 pixels. Divided by 27 inches that gives 163 PPI.

Context makes the number meaningful. A 27-inch 1440p monitor sits at 109 PPI, a 24-inch 1080p at 92 PPI, and a 32-inch 4K at 138 PPI. Anything from roughly 90 PPI upwards is workable at a typical 60 cm desk distance; from about 140 PPI text becomes noticeably smoother, and beyond 200 PPI the returns are small.

There is a catch on the desktop. Very high density often forces operating-system scaling, and scaling quality varies — well on macOS, unevenly on Windows depending on the application. A 27-inch 1440p screen at 109 PPI runs unscaled and is why that combination remains a popular default despite 4K being cheap.

Key facts

PPI formula

Diagonal pixel count divided by the diagonal in inches.

27-inch 4K

163 PPI — sharp, but usually needs operating-system scaling.

27-inch 1440p

109 PPI, which runs unscaled and stays comfortable for text.

24-inch 1080p

92 PPI, about the practical floor for desk work.

Desk distance

At 50 to 70 cm the eye resolves far more detail than at television distance.

Scaling is the catch

High density means fractional scaling, which some Windows applications still handle poorly.

How to get it right

1

Get the diagonal in pixels

Square the horizontal and vertical counts, add them, take the square root.

2

Divide by the size

Divide that figure by the diagonal in inches to get PPI.

3

Convert the physical size

Multiply the diagonal in inches by 2.54 for centimetres if you need to check desk fit.

4

Sanity-check scaling

Anything above roughly 140 PPI will likely need scaling — confirm your tools handle it well.

Questions people ask

About 163 PPI. The diagonal holds 4,405 pixels, and dividing by 27 gives 163.

Keep reading

TV & monitor screen sizes

What a screen size in inches actually measures, how wide each popular size really is, and how to check a TV fits before it arrives.

Height: feet, inches and cm

How to convert height between feet, inches and centimetres without the classic 5.10 mistake, plus a chart of common adult heights.

Weight: kg, pounds and stone

Convert body weight between kilograms, pounds and stone accurately — including why the 2.2 shortcut fails at higher weights.

Check a monitor size in centimetres

Inch-to-centimetre pages give exact width and height for every panel size.

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