Runs in your browser · nothing is uploaded

Screen Size & PPI Calculator

Enter a screen's diagonal into this PPI calculator into this PPI calculator and resolution to get its pixel density (PPI), physical width and height, and aspect ratio — for two displays at once, so you can see exactly how a monitor upgrade compares.

Diagonal inches

Pixel width

Pixel height

Comparison diagonal inches

Comparison pixel width

Comparison pixel height

Diagonal sizes are in inches; dimensions assume square pixels and the stated active-screen diagonal.

PPI screen 1: 108.79
PPI screen 2: 91.79

Screen	PPI	Width inches	Height inches	Aspect ratio
Screen 1	108.79	23.53	13.24	1.78:1
Screen 2	91.79	20.92	11.77	1.78:1

How PPI and screen size are calculated

Pixel diagonal√(width px² + height px²)
Pixel densityPPI = pixel diagonal ÷ diagonal in inches
Physical sizewidth in = width px ÷ PPI; height in = height px ÷ PPI
Aspect ratiowidth px ÷ height px, shown as x.xx:1 (16:9 = 1.78:1)

Diagonal sizes are in inches; dimensions assume square pixels and the stated active-screen diagonal. Enter sizes in inches; to convert centimeters, divide by 2.54. Results update as you type and can be saved as a text file. The preset buttons fill screen 1 with a 27-inch QHD, 24-inch Full HD or 32-inch 4K monitor.

Don't know your screen's exact size? Measure the lit picture area from one corner to the opposite corner, leaving out the bezel. Your resolution is in your operating system's display settings — use the native resolution, not a scaled "looks like" value, or the PPI will come out too low. Fill in screen 2 with the monitor you're considering to compare them row by row.

Worked example

Upgrading from a 24-inch 1920 × 1080 monitor to a 27-inch 2560 × 1440 one:

Measure	27" QHD	24" Full HD
PPI	108.79	91.79
Width (in)	23.53	20.92
Height (in)	13.24	11.77
Aspect ratio	1.78:1	1.78:1

The 27-inch screen's pixel diagonal is √(2560² + 1440²) ≈ 2937.2, and 2937.2 ÷ 27 = 108.79 PPI. It has about 27% more screen area but 78% more pixels, so you get more room and crisper text.

Pixel density of common screens

Whether a density is "sharp enough" depends on how far away you sit. A common rule of thumb: with 20/20 vision you resolve detail about one arcminute across, so pixels stop being visible beyond roughly 3,438 ÷ PPI inches. That's why a phone needs far more pixels per inch than a TV across the room.

Screen	Resolution	PPI	Size (in)	Pixels blend beyond
6.1-inch phone	2532 × 1170	457.25	5.54 × 2.56	8 in (19 cm)
13.3-inch laptop	2560 × 1600	226.98	11.28 × 7.05	15 in (38 cm)
15.6-inch laptop	1920 × 1080	141.21	13.60 × 7.65	24 in (62 cm)
24-inch Full HD	1920 × 1080	91.79	20.92 × 11.77	37 in (95 cm)
27-inch QHD	2560 × 1440	108.79	23.53 × 13.24	32 in (80 cm)
27-inch 4K	3840 × 2160	163.18	23.53 × 13.24	21 in (54 cm)
32-inch 4K	3840 × 2160	137.68	27.89 × 15.69	25 in (63 cm)
34-inch ultrawide	3440 × 1440	109.68	31.36 × 13.13	31 in (80 cm)
55-inch 4K TV	3840 × 2160	80.11	47.94 × 26.96	43 in (109 cm)

Desk monitors

OSHA's workstation guidance puts a monitor at least 20 inches from your eyes, and many people sit 20 to 30 inches away. A 24-inch 1080p screen's pixels stay visible out to about 37 inches, which is why small text on it can look soft; a 27-inch 4K blends at about 21 inches and looks crisp.

Scaling

High-density screens draw text and icons with more pixels rather than making them tiny. At 150% scaling a 3840 × 2160 screen gives the workspace of 2560 × 1440, and at 200% that of 1920 × 1080 — the same layout, with finer detail. PPI itself never changes.

Comparing shapes

Diagonals mislead across aspect ratios: a 34-inch ultrawide is wide but not tall. Compare the width and height columns instead. To work out sizes for a ratio, use the Aspect Ratio Calculator.

Sources: US Occupational Safety and Health Administration, Computer Workstations eTool, "Monitors"; Snellen visual acuity convention (20/20 letter details subtend one minute of arc). The blending distance is a rule of thumb, not a vision test. Checked 15 October 2026.

Frequently asked questions

How do I calculate PPI?+

Find the diagonal resolution in pixels with Pythagoras — √(width² + height²) — and divide it by the diagonal size in inches. A 27-inch 2560 × 1440 monitor has a pixel diagonal of about 2,937, so its density is 108.79 PPI.

Is a 27-inch 1440p monitor sharper than a 24-inch 1080p one?+

Yes. The 27-inch 2560 × 1440 screen has 108.79 PPI against 91.79 PPI for a 24-inch 1920 × 1080, so text looks noticeably crisper even though the screen is bigger. It's also 23.53 inches wide instead of 20.92.

What's the difference between PPI and DPI?+

PPI (pixels per inch) describes a screen or a digital image: how many pixels fit in an inch. DPI (dots per inch) strictly describes printers, which build each pixel from many ink dots. Monitor makers and mouse settings often say DPI when they mean PPI or counts per inch; for screens, the numbers here are PPI.

How wide and tall is my screen?+

Enter its diagonal and resolution: the calculator gives the width and height of the visible picture in inches. A 27-inch 16:9 screen is 23.53 × 13.24 inches (59.8 × 33.6 cm). Add the bezels and stand to that before checking whether it fits your desk.

At what distance can I no longer see individual pixels?+

A common rule of thumb uses 20/20 vision, which resolves detail about one arcminute across. On that basis pixels blend together beyond about 3,438 ÷ PPI inches: 37 inches (95 cm) for a 24-inch 1080p monitor, 32 inches (80 cm) for a 27-inch 1440p and 21 inches (54 cm) for a 27-inch 4K. Sharper eyes can see finer detail, so treat it as a guide.

Does a 4K monitor have the same PPI at every size?+

No — the same pixels spread over a bigger area are less dense. 3840 × 2160 gives 163.18 PPI at 27 inches but 137.68 PPI at 32 inches. That's why a 32-inch 4K screen is often comfortable at lower scaling than a 27-inch one.

Does display scaling change the PPI?+

No. PPI is fixed by the hardware. Scaling in Windows or macOS only changes how many pixels the system uses to draw each element, so text and buttons stay a comfortable size. A 4K screen at 150% scaling gives you the workspace of a 2560 × 1440 screen, drawn with sharper detail.

What is a good PPI for a monitor?+

It depends on how far away you sit and whether you use scaling. As a rough guide for a desk monitor, about 90–110 PPI looks fine at 100% scaling — a 24-inch 1080p is 91.79 and a 27-inch 1440p 108.79. Around 140 PPI and up, such as a 27-inch 4K at 163.18, gives visibly crisper text but usually needs 150% or more scaling so text isn't tiny.

Why is the aspect ratio shown as 1.78:1 instead of 16:9?+

The calculator divides width by height and shows the result as a decimal, which works for any resolution, including odd ones. 1.78:1 is 16:9 (16 ÷ 9 ≈ 1.78), 1.60:1 is 16:10, and a 3440 × 1440 "21:9" ultrawide is actually 2.39:1, a little wider than 21 ÷ 9 ≈ 2.33.

Does it work for ultrawide monitors, TVs and phones?+

Yes — any screen with a known diagonal and resolution, up to 500 inches. A 34-inch 3440 × 1440 ultrawide has 109.68 PPI and is 31.36 inches wide; a 65-inch 4K TV has just 67.78 PPI, which looks sharp because you watch it from across the room. For phones, use the full screen resolution, not the scaled resolution the operating system reports.

Why doesn't my result match the spec sheet?+

Advertised sizes are often rounded — a "27-inch" panel may measure 27.0 or 26.9 inches — and some phones and laptops quote the diagonal of a full rectangle even when the corners are rounded or there's a notch. Diagonal sizes are in inches; dimensions assume square pixels and the stated active-screen diagonal.

Is anything I enter sent or stored?+

No. The figures are calculated in your browser as you type, nothing is stored, and the optional results file is created on your device.