Screen PPI Calculator
Work out how sharp a display is from three numbers: its horizontal and vertical resolution and its diagonal size in inches. The calculator returns pixels per inch (PPI), the dot pitch (the distance between pixels), the total megapixels and a quality class from standard through to “retina” densities. A higher PPI packs more pixels into each inch, so a 5-inch phone at 1080p looks far sharper than a 27-inch monitor at the same resolution, even though both are 1920 × 1080.
How to use this tool
- Enter the display’s horizontal and vertical resolution in pixels.
- Enter the diagonal screen size in inches.
- Read the pixel density (PPI), dot pitch and quality class.
- Compare two screens by running each and looking at the PPI.
- Remember that ideal sharpness also depends on how far away the screen is viewed.
The formula
Pixel density measures how tightly packed a display’s pixels are. The diagonal in pixels comes from Pythagoras; dividing by the diagonal in inches gives pixels per inch. Density, not resolution alone, determines whether individual pixels are visible.
diagonal_px = √(width² + height²)
PPI = diagonal_px ÷ diagonal_inches
dot_pitch_mm = 25.4 ÷ PPI- diagonal_px
- Display diagonal measured in pixels
- diagonal_inches
- The size manufacturers advertise
- dot pitch
- Distance between pixel centres, in millimetres
Whether a display looks sharp depends on viewing distance as well as density. A phone held at 30 cm needs roughly 300 PPI for pixels to be indistinguishable; a television across a room needs far less.
Worked examples
27-inch 1080p monitor
- Given
- 1920 × 1080, 27"
- Result
- ≈ 81.6 PPI
Diagonal in pixels = √(1920² + 1080²) ≈ 2202.9; dividing by 27 inches gives about 81.6 PPI — a fairly low density for its size.
5-inch 1080p phone
- Given
- 1080 × 1920, 5"
- Result
- ≈ 440 PPI
The same pixel count on a 5-inch diagonal packs about 440 PPI — “retina” class, and why phones look sharp up close.
27-inch 4K monitor
- Given
- 3840 × 2160, 27"
- Result
- ≈ 163 PPI
Quadrupling the pixels on the same 27-inch panel roughly doubles the PPI to about 163, a marked jump in sharpness.
Frequently asked questions
PPI is pixels per inch — a display’s pixel density. It is calculated by taking the diagonal resolution in pixels, √(width² + height²), and dividing by the diagonal size in inches. Higher PPI means smaller, more tightly packed pixels and a sharper image at a given viewing distance.
PPI (pixels per inch) describes screens; DPI (dots per inch) describes printing. They are often used interchangeably, but strictly PPI is about display pixel density while DPI is about the dots a printer lays down. For print sharpness, use the print resolution calculator instead.
Apple’s “retina” marketing refers to a density high enough that a typical viewer cannot distinguish individual pixels at normal viewing distance — roughly 300+ PPI for phones held close, but lower for laptops and monitors viewed further away. This calculator classifies density into bands, but the perceived threshold shifts with distance.
Because resolution alone does not determine sharpness — size does too. 1920×1080 spread across a 27-inch monitor is about 82 PPI, but the same pixels on a 5-inch phone are around 440 PPI. Same pixel count, very different density and sharpness.
Dot pitch is the physical distance between adjacent pixels, usually in millimetres — effectively the inverse of PPI. A smaller dot pitch means a denser, sharper display. It is a useful figure for professional and close-viewing work where individual pixels matter.
Related tools
Work out megapixels, aspect ratio and print size from any resolution, HD through 8K.
Aspect Ratio CalculatorSimplify any ratio, scale dimensions while keeping proportions, and match common formats.
Print Resolution CalculatorWork out the pixel dimensions, print size or DPI you need for sharp printed output.