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Calcimator

Screen PPI Calculator

Calculate pixels per inch (PPI), dot pitch, aspect ratio, and physical dimensions of any display.

This calculator derives pixel density and physical screen dimensions from just three numbers: horizontal resolution, vertical resolution, and diagonal screen size. It first combines the two resolutions into a diagonal pixel count using the Pythagorean theorem, then divides that by Screen Size (Diagonal) to get Pixels Per Inch (PPI) -- which is why the diagonal measurement, not either resolution number alone, has the single biggest effect on the result: the same 2560x1440 panel crammed into a 13-inch laptop screen reads as noticeably sharper than the identical resolution stretched across a 43-inch monitor. Dot Pitch is simply the reciprocal of PPI expressed in millimeters (25.4 divided by PPI), so it moves inversely to pixel density -- a smaller dot pitch means a sharper display. Width and height in inches are back-calculated by splitting the diagonal proportionally between the two resolution axes using the same aspect ratio as the pixel counts, and Aspect Ratio itself is reduced to its simplest whole-number form via the greatest common divisor of the two resolution values. Density Class is not a fixed PPI threshold: "Retina" is fundamentally a viewing-distance criterion, roughly one arcminute of visual angle per pixel, so the calculator converts PPI and your entered Viewing Distance into Pixels Per Degree (PPD) and classifies from that instead. A 27-inch 5K panel viewed from 24 inches away reads as "Retina-class at this distance" even though its raw PPI is under 220, while the same panel viewed from across a room would not need anywhere near that density to look equally sharp.

Inputs

px
px
inches
in

Results

Pixels Per Inch (PPI)

108.79

Dot Pitch0.23 mm
Total Pixels3,686,400
Megapixels3.69 MP
Aspect Ratio16:9
Screen Width23.53 in
Screen Height13.24 in
Screen Area311.5 sq in
Density ClassSharp, pixels visible on fine detail
Pixels Per Degree45.6 PPD
Retina Threshold at This Distance143.2 PPI
How to Use This Calculator
  1. Enter the screen's Width Resolution and Height Resolution in pixels (e.g., 2560 × 1440 for a QHD monitor).
  2. Set the Screen Size (Diagonal) in inches — check the manufacturer's spec sheet or the back of the display.
  3. The calculator instantly shows Pixels Per Inch (PPI) and Dot Pitch in mm.
  4. Review Total Pixels and Megapixels to understand the overall pixel count.
  5. Enter the viewing distance (about 12 in for a phone, 24 in for a monitor, 100 in for a TV) and read Pixels Per Degree alongside the Retina Threshold at This Distance to see whether the display resolves beyond the eye's limit.

How the result changes with Screen Size (Diagonal)

Screen Size (Diagonal)Pixels Per Inch (PPI)
13225.94
4368.31
7837.66
10827.2

What each input means

Width Resolution
Screen width in pixels.
Height Resolution
Screen height in pixels.
Screen Size (Diagonal)
Screen diagonal size in inches.
Viewing Distance
Typical distance from the eye to the screen: about 12 in for a phone, 24 in for a monitor, 100 in for a TV. Drives the Retina/Density classification.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    Width Resolution = 2560, Height Resolution = 1440, Screen Size (Diagonal) = 27 = 3 input(s) provided
  2. Calculate Pixels Per Inch
    Pixels Per Inch
    108.79 = 108.79
  3. Calculate Dot Pitch
    Dot Pitch
    0.233 = 0.233
  4. Calculate Total Pixels
    Total Pixels = widthPixels * heightPixels
    3686400 = 3686400

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

Frequently Asked Questions

Why does screen size affect sharpness more than resolution alone?

Because Pixels Per Inch is diagonal pixel count divided by Screen Size (Diagonal), and shrinking the diagonal concentrates the same pixel count into a smaller physical area. A 2560x1440 resolution on a 13-inch panel produces a noticeably higher PPI, and a visibly sharper image, than the same resolution spread across a 43-inch panel.

What does Dot Pitch actually measure, and how is it related to PPI?

Dot Pitch is the physical distance between adjacent pixel centers, in millimeters, calculated as 25.4 divided by PPI. It moves in the opposite direction from PPI: as pixel density rises, the individual pixels sit closer together, so Dot Pitch gets smaller, not larger.

How is the Aspect Ratio figure calculated from the resolution?

The calculator finds the greatest common divisor of your Width Resolution and Height Resolution values, then divides both by it to reduce the ratio to its simplest whole-number form -- 2560x1440 reduces to 16:9, for example, the same way a fraction gets reduced to lowest terms.

Are Screen Width and Screen Height just the pixel counts divided by PPI?

Yes, exactly. The calculator splits Screen Size (Diagonal) proportionally between the two axes using the pixel aspect ratio, but that is algebraically the same thing: width_inches = width_px / PPI, because PPI is itself diagonal pixels divided by diagonal inches. A 2560x1440 panel at 27 inches gives 108.79 PPI, and 2560 / 108.79 = 23.53 inches wide -- the same figure the calculator reports.

Is there a single PPI number that counts as Retina?

No, and any calculator that gives you one is oversimplifying. Retina is a viewing-distance criterion -- roughly one arcminute per pixel, or about 60 pixels per degree of visual angle -- so the same PPI can be "Retina" at arm's length and clearly not at across-the-room distance. Apple's own Retina products bear this out: the 27-inch 5K iMac is about 218 PPI, MacBook Pro panels run 220 to 254 PPI, and iPhones run 326 to 460 PPI, held much closer to the eye.

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