PPI Calculator — Pixel Density from Resolution and Screen Size
Calculate a screen’s pixel density (PPI) from its resolution and diagonal size — or the diagonal from the resolution and PPI, or PPI from the width and height — with dot pitch, aspect ratio, physical size, retina viewing distance and a comparison with popular phones, laptops, monitors and TVs.
How it works
Diagonal pixels = √(width² + height²) · PPI = diagonal pixels ÷ diagonal inches · Diagonal = diagonal pixels ÷ PPI · Dot pitch (mm) = 25.4 ÷ PPI · Width = pixels ÷ PPI · Pixels blend beyond 1 ÷ (PPI × tan 1′) ≈ 3,438 ÷ PPI inches
Pixel density is the number of pixels along the screen’s diagonal divided by the diagonal size in inches. The diagonal pixel count comes from Pythagoras: √(width² + height²). Higher PPI means sharper text and images; phones usually sit between 400 and 500 PPI, laptops between 140 and 260, desktop monitors between 90 and 220, and TVs below 100 because they are watched from across the room. The calculator works three ways: PPI from the resolution and advertised diagonal, the diagonal from the resolution and a PPI figure (useful when a spec sheet gives density but not size), and PPI from a measured width and height of the visible picture, which also flags measurements that don’t match the aspect ratio. Alongside PPI it gives pixels per centimetre, dot pitch, total megapixels, the reduced aspect ratio, the physical width, height and area, the Android density class, pixels per degree at your viewing distance and the distance beyond which 20/20 vision can no longer pick out pixels (one arcminute per pixel, the idea behind Apple’s “Retina” label). Pick a phone, tablet, laptop, monitor or TV to compare side by side, and see how the same resolution would look at common screen sizes.
Worked example
A 1920×1080 laptop with a 15.6-inch screen: the diagonal is √(1920² + 1080²) = √4,852,800 = 2,202.91 pixels, so PPI = 2,202.91 ÷ 15.6 = 141.21. The dot pitch is 25.4 ÷ 141.21 = 0.1799 mm, the panel is 13.6 × 7.65 inches (34.5 × 19.4 cm), and individual pixels blend together beyond about 24.3 inches (62 cm). The same resolution on a 24-inch monitor is only 91.8 PPI, while a 27-inch 4K monitor reaches 163.2 PPI.
Frequently asked questions
What PPI looks "retina"?
It depends on viewing distance. With 20/20 vision one pixel must span less than one arcminute, so pixels disappear beyond roughly 3,438 ÷ PPI inches: about 300 PPI at 11–12 inches for a phone, about 220 PPI at 16 inches for a laptop, and about 110 PPI at 31 inches for a monitor. The calculator shows that distance and the pixels per degree at your own distance — 60 PPD or more is retina-class.
How do I find the screen size from the resolution and PPI?
Divide the diagonal pixel count by the PPI. For a 2560×1440 screen at 109 PPI, √(2560² + 1440²) = 2,937.2 pixels, and 2,937.2 ÷ 109 = 26.9 inches — a 27-inch monitor. Choose “Diagonal from PPI”.
Is PPI the same as DPI?
Not strictly. PPI counts pixels on a screen or in a digital image; DPI counts ink dots a printer lays down, and a printer uses several dots per pixel. People often say DPI for screens, and Android’s density classes (mdpi, xhdpi…) use “dpi” for pixel density.
Why is my phone maker’s PPI slightly different?
Advertised diagonals are rounded and some phones have rounded corners or notches, so makers compute PPI from the exact panel size. A difference of a few PPI is normal.
Is higher PPI always better?
It is sharper, but past the point your eyes can resolve at your viewing distance the gain is small, and more pixels cost GPU power and battery. On a desktop monitor at arm’s length, about 110–140 PPI looks crisp at 100–125% scaling; 160+ PPI usually needs 150–200% scaling for readable text.
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This calculator is for educational purposes. Double-check important results before acting on them.