PPI Calculator

Pixels per inch measures how densely pixels are packed on a display. A higher PPI value means finer detail and sharper text at any given viewing distance. PPI is derived here from screen resolution and diagonal measurement, along with dot pitch and physical width and height, so displays can be compared objectively.

Horizontal and vertical resolution are entered in pixels; common pairings are 1920 by 1080 for Full HD, 2560 by 1440 for QHD, and 3840 by 2160 for 4K UHD. Diagonal size is entered in inches, measured from one corner of the screen to the opposite corner. All three fields accept whole numbers, decimals, fractions such as 3/4, and mixed numbers such as 5 1/2, so a screen measured as 15 3/4 inches can be entered exactly.

PPI is computed as the square root of horizontal pixels squared plus vertical pixels squared, divided by the diagonal size: PPI = sqrt(width^2 + height^2) / diagonal. Dot pitch in millimeters equals 25.4 divided by PPI, since there are 25.4 millimeters to an inch. Physical screen width equals horizontal pixels divided by PPI, and physical height equals vertical pixels divided by PPI. The result also reports total pixel count and the simplified aspect ratio.

A 1920 by 1080 display with a 24 inch diagonal, the calculator's own defaults, gives PPI = sqrt(1920^2 + 1080^2) / 24 = sqrt(3,686,400 + 1,166,400) / 24 = sqrt(4,852,800) / 24, about 2202.91 / 24, or roughly 91.79 PPI. Dot pitch is 25.4 / 91.79, about 0.28 millimeters. Physical width is 1920 / 91.79, about 20.9 inches, and physical height is 1080 / 91.79, about 11.8 inches, a ratio that checks out at 16:9.

Settings switches the physical dimension output between inches and centimeters, adjusts the number of decimal places shown, and can enable a step-by-step formula view that shows the symbolic formula, the substituted values, and the computed answer for each result. Inputs and settings persist in local storage, so they remain available on return; resetting restores the defaults above.

Screen pixel density influences readability, design fidelity, and purchasing decisions across many fields. Knowing the exact PPI and physical dimensions of a display helps match hardware to workflow requirements.

• Graphic Design: Compare monitor PPI values to determine which display renders a 72 DPI web mockup at true physical size versus a scaled approximation. Enter 2560 by 1440 on a 27 inch panel to see whether fine typography remains legible without OS-level scaling.
• Photography and Print: Verify that a retina display has enough density to soft-proof a 300 DPI print image at 100 percent zoom. Knowing physical screen width helps gauge how much of a wide panorama fits on screen without scrolling.
• Gaming: Evaluate whether a 4K resolution on a 32 inch monitor produces a meaningfully higher PPI than 1440p on a 27 inch panel, and decide if the GPU cost of driving extra pixels translates to visible sharpness at a typical desk distance.
• Laptop Shopping: Compare the dot pitch of a 13.3 inch 1920 by 1080 laptop against a 14 inch 2560 by 1600 model to quantify the sharpness difference before purchasing.
• Mobile Development: Enter phone screen specs such as 1170 by 2532 on a 6.1 inch diagonal to verify the PPI bucket (standard, retina, super retina) and choose the correct asset density for app icons and splash screens.
• Accessibility Auditing: Calculate physical text height at a given font size by combining PPI with CSS pixel ratios, helping confirm that body text meets minimum legibility guidelines on a target device.
• Signage and Large Displays: Determine whether a 55 inch 1080p commercial display provides adequate dot pitch for text-heavy content viewed at two meters, or whether a 4K panel is necessary.
• Education: Demonstrate the Pythagorean theorem in a practical context by showing how diagonal pixel count is derived from width and height, reinforcing the formula with tangible hardware examples.