PPI and screen size calculator

Start with the screen’s own specification

Enter the panel’s native pixel resolution, then the diagonal of its viewable area. The diagonal runs between opposite corners of the image, excluding the bezel. Get it from the manufacturer’s specification or measure it yourself. The calculator starts with a QHD, 27-inch example. Replace both values with your display’s specifications. A resolution preset changes only the pixel counts; check the diagonal yourself.

Use whole numbers for width and height, without thousands separators. For the diagonal, use a decimal point in this English edition or a decimal comma in the Portuguese edition. Values must be within 1–100,000 pixels on each side and 0.1–1,000 inches, equivalent to 0.254–2,540 centimeters. These ranges define the inputs accepted by the calculator. Empty, zero, negative, fractional pixel counts and malformed numbers clear the affected result until corrected.

Read the result

• PPI: pixels per inch along the display. At 2560 × 1440 pixels and a 27-inch diagonal, the result is about 108.8 PPI.
• Screen width and height: the estimated dimensions of the active image. These exclude the bezel, stand and any casing, so use the manufacturer’s outer dimensions when planning desk space.
• Pixel pitch: the calculated distance between adjacent pixel centers in millimeters, under the square-pixel assumption. A smaller pitch corresponds to higher PPI.
• Aspect ratio and area: the width-to-height ratio reduced to whole numbers and the calculated rectangular image area. A rotated screen swaps its width and height but keeps the same density and area.

The calculation treats the active image as a flat rectangle with square pixels. For curved panels, cutouts, rounded corners or non-square pixels, treat the dimensions as a rectangular approximation. Result precision depends on the entered diagonal, which may be rounded in the specification.

Compare two displays fairly

Turn on Add display B to enter a separate resolution and diagonal. The example B is 3840 × 2160 at 27 inches. It has the same calculated physical width and height as the 27-inch QHD example, with 50% higher pixel density. The higher density means closer pixel spacing. The detail you perceive also depends on viewing distance, content and rendering.

Two screens can have equal PPI while differing in size and resolution. Two screens with the same resolution have different PPI when their diagonals differ. For very small density differences, the result shows extra decimal places to help you compare. Viewing distance, eyesight, text rendering, image content and the display itself also affect the detail you perceive.

How the calculation works

For pixel width W, pixel height H and physical diagonal D in inches, the pixel diagonal is √(W² + H²). PPI is that pixel diagonal divided by D. Physical width is W ÷ PPI and height is H ÷ PPI, both in inches. Pixel pitch is 25.4 ÷ PPI millimeters; rectangular area is physical width × height. We use 1 inch = 2.54 centimeters, consistent with the NIST conversion table.

Changing units keeps the unrounded physical value internally. It changes how the dimensions are shown, so repeated switches do not repeatedly round and shrink the diagonal. Results are rounded for reading; the entered specification still determines their useful precision.

Where to find the physical diagonal

CSS pixels describe page layout. They are not a direct measurement of panel pixels or physical size. The W3C explanation of CSS length units describes why a CSS inch need not match a physical inch on a screen. Use the manufacturer’s viewable diagonal or your own physical measurement for this calculator.

Use the native panel resolution to calculate its physical density, even if your system currently sends a lower-resolution image. Scaling changes the size of the interface and may affect rendering; it does not add or remove pixels from the panel. See screen and viewport information for the separate values the browser reports.

This calculator processes your entries on this device without uploading or automatically saving them. A settings link includes the entered values in its URL fragment; share it only when you want someone else to receive those settings. Switching language preserves the physical meaning and the comparison choice. Use Reset to examples to return to the starting setup. To observe the display instead, open screen inspection, or follow the new-monitor checklist.