PPI Calculator Widget

A pixel-density calculator for tech reviews and buying guides. Readers enter a screen's resolution and diagonal, or pick a preset, and see its pixels per inch, dot pitch in millimetres and physical width and height.

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<iframe src="https://a2z.tools/embed/w/ppi-calculator" title="PPI Calculator by A2Z Tools" width="100%" height="650" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>

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How it works

A screen's pixel density is its diagonal measured in pixels divided by its diagonal measured in inches. The pixel diagonal follows from Pythagoras: a 2560 x 1440 panel has sqrt(2560^2 + 1440^2) = 2,937 pixels corner to corner, so at 27 inches it has 108.8 pixels per inch. Dot pitch, the distance between neighbouring pixel centres, is 25.4 mm divided by the PPI - 0.2335 mm here. The widget also turns the diagonal back into the visible width and height and gives the megapixel count. Presets cover three Apple devices, whose resolutions, diagonals and stated ppi come from Apple's own tech-spec pages, plus four typical monitor and TV sizes. For the Apple devices the stated figure is shown next to the calculated one: the MacBook Air 13.6-inch works out at 224.5 against Apple's 224, while the iPhone 15 gives 461 against 460 because Apple quotes the diagonal of a screen with rounded corners.

Calculation method

  • Diagonal in pixels = sqrt(width^2 + height^2)
  • PPI = diagonal in pixels / diagonal in inches
  • Dot pitch (mm) = 25.4 / PPI
  • Visible width = diagonal x width / diagonal in pixels; height likewise

Worked examples

27-inch QHD monitor

Inputs: 2560 x 1440 px, 27 in

Result: 108.8 PPI; dot pitch 0.2335 mm; 23.53 x 13.24 in visible

sqrt(2560^2 + 1440^2) = 2,937.2 px / 27 in.

MacBook Air 13.6-inch preset

Inputs: 2560 x 1664 px, 13.6 in

Result: 224.5 PPI (Apple states 224)

sqrt(2560^2 + 1664^2) = 3,053.2 px / 13.6 in.

Limitations

  • Assumes square pixels and a rectangular screen; notches and rounded corners are ignored.
  • Does not account for scaling settings (for example 200% on Retina displays) that change how big text looks.
  • Presets are a small sample; other devices need their specifications typed in.

Where publishers use it

  • Phone and laptop review sites comparing sharpness across models
  • Monitor buying guides explaining why 27-inch 4K looks crisper than 27-inch QHD
  • UI designers checking how large a 1px line or 12px text will look on a target device
  • Digital-signage suppliers matching panel density to viewing distance
  • Tech classrooms teaching resolution, density and Pythagoras with a real example

Questions

What PPI looks sharp?

At a typical 50-60 cm desk distance, around 110 PPI looks acceptable and 160 PPI or more looks crisp. Phones held at 30 cm need roughly 300 PPI or more before individual pixels disappear for most people.

Why is my result slightly different from the manufacturer's?

Makers round the diagonal (a 6.1-inch phone may really be 6.12 inches) and measure screens with rounded corners as if they were rectangles. The iPhone 15 calculates at 461 PPI against Apple's 460.

What is dot pitch?

The distance from the centre of one pixel to the next, in millimetres. It is 25.4 divided by the PPI: a 24-inch Full HD monitor (91.8 PPI) has a 0.277 mm pitch.

Is PPI the same as DPI?

PPI describes a screen or an image's pixels; DPI originally describes printer dots. For printing an image at a given size, use the DPI calculator instead.

Can I preset a screen for my article?

Yes: link with v_preset=custom&v_w=3840&v_h=2160&v_diag=32 to open on your figures.

Sources

  1. iPhone 15 - Tech Specs - Apple Support . 6.1-inch (diagonal), 2556-by-1179-pixel resolution at 460 ppi. Checked 2026-10-01.
  2. MacBook Air (M2, 2022) - Tech Specs - Apple Support . 13.6-inch (diagonal), 2560-by-1664 native resolution at 224 pixels per inch. Checked 2026-10-01.
  3. MacBook Pro (16-inch, 2023) - Tech Specs - Apple Support . 16.2-inch (diagonal), 3456-by-2234 native resolution at 254 pixels per inch. Checked 2026-10-01.

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A2Z Tools PPI Calculator
https://a2z.tools/embed/ppi-calculator

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