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PPI Calculator

PhotographyImage Size and Print

Measured corner to corner across the visible area.

Pixel density (PPI) —
Diagonal in pixels
—
Dot pitch (mm)
—
Screen width (in)
—
Screen height (in)
—
Total megapixels
—

PPI equals the diagonal resolution in pixels divided by the diagonal size in inches. For a 27-inch 2560 × 1440 monitor, √(2560² + 1440²) = 2937.21 pixels, and 2937.21 ÷ 27 = 108.79 PPI. Enter any width, height and diagonal to get the density, dot pitch and physical panel dimensions.

About this tool

Pixel density decides how sharp text and photos look on a screen. Photographers comparing editing monitors, buyers weighing a 27-inch QHD against a 32-inch 4K panel, and developers picking a scaling factor all need the same figure. Type the horizontal and vertical resolution and the advertised diagonal, and the calculator returns pixels per inch, the diagonal length in pixels, the dot pitch in millimetres, the physical width and height of the visible area, and the total megapixel count, with the working shown line by line. One limit: it assumes square pixels and a diagonal measured over the visible image. Manufacturers often round the diagonal (a 27-inch panel may really be 26.9 inches), so the result can differ from a spec sheet by a fraction of a percent.

How to use it

  1. Enter the resolution

    Type the native horizontal and vertical pixel counts, such as 1920 and 1080.

  2. Enter the diagonal

    Give the screen size in inches as listed by the maker, measured corner to corner.

  3. Read the density

    PPI, dot pitch, panel width and height and megapixels update as you type, with the working underneath.

Examples

24-inch Full HD monitor

Horizontal resolution
1920
Vertical resolution
1080
Diagonal screen size
24

Result Pixel density (PPI): 91.79
Diagonal in pixels: 2,202.91
Dot pitch (mm): 0.2767
Screen width (in): 20.92
Screen height (in): 11.77
Total megapixels: 2.07

  1. Diagonal in pixels = √(1920² + 1080²) = 2202.91
  2. PPI = 2202.91 ÷ 24 in = 91.79
  3. Dot pitch = 25.4 ÷ 91.79 = 0.2767 mm
  4. Screen size = 20.92 × 11.77 in

A common office screen sits just above 90 PPI, which is why text looks soft next to a laptop.

27-inch QHD monitor

Horizontal resolution
2560
Vertical resolution
1440
Diagonal screen size
27

Result Pixel density (PPI): 108.79
Diagonal in pixels: 2,937.21
Dot pitch (mm): 0.2335
Screen width (in): 23.53
Screen height (in): 13.24
Total megapixels: 3.69

  1. Diagonal in pixels = √(2560² + 1440²) = 2937.21
  2. PPI = 2937.21 ÷ 27 in = 108.79
  3. Dot pitch = 25.4 ÷ 108.79 = 0.2335 mm
  4. Screen size = 23.53 × 13.24 in

2560 × 1440 at 27 inches lands near 109 PPI, a popular balance for desktop work at 100% scaling.

27-inch 4K display

Horizontal resolution
3840
Vertical resolution
2160
Diagonal screen size
27

Result Pixel density (PPI): 163.18
Diagonal in pixels: 4,405.81
Dot pitch (mm): 0.1557
Screen width (in): 23.53
Screen height (in): 13.24
Total megapixels: 8.29

  1. Diagonal in pixels = √(3840² + 2160²) = 4405.81
  2. PPI = 4405.81 ÷ 27 in = 163.18
  3. Dot pitch = 25.4 ÷ 163.18 = 0.1557 mm
  4. Screen size = 23.53 × 13.24 in

Moving from QHD to 4K on the same 27-inch panel raises density by half, to about 163 PPI.

How it is calculated

PPI = √(W² + H²) ÷ D; dot pitch = 25.4 ÷ PPI

W
horizontal resolution in pixels
H
vertical resolution in pixels
D
diagonal size in inches

Pythagoras gives the number of pixels along the diagonal. Dividing by the diagonal length gives pixels per inch, which holds in every direction when pixels are square. Dot pitch is the distance between pixel centres: 25.4 mm per inch divided by PPI. The physical width is D × W ÷ diagonal pixels, and the height follows the same way with H.

When not to use it

  • Do not use it to set print resolution for a photo; that depends on print size, not a screen.
  • It does not apply to panels with non-square pixels or anamorphic scaling.
  • It cannot tell you perceived sharpness without also knowing the viewing distance.

Common mistakes

  • Entering the scaled desktop resolution instead of the panel's native resolution.
  • Typing the diagonal in centimetres when the field expects inches.
  • Treating PPI and printer DPI as the same measure.

Frequently asked questions

What PPI counts as a sharp monitor?

At a typical desk distance of 60 to 70 cm, around 110 PPI looks clean at 100% scaling, and 160 PPI or more looks crisp with 150% to 200% scaling. Below about 90 PPI, individual pixels and fringed text edges become visible to most people.

Why does my result differ from the spec sheet?

Makers round the diagonal. A panel sold as 27 inches may have a 26.9-inch visible area, and phones are often quoted to one decimal. A small change in the diagonal shifts PPI by the same proportion, so a 0.4% difference is normal.

What is the difference between PPI and DPI?

PPI counts pixels on a display or in an image file per inch of output. DPI counts ink dots a printer lays down, and a printer uses several dots to reproduce one pixel's colour. The two are often used loosely as synonyms, but only PPI describes a screen.

What does dot pitch tell me?

Dot pitch is the spacing between neighbouring pixel centres in millimetres. A 24-inch 1080p monitor has a pitch of about 0.277 mm; a 27-inch 4K panel is about 0.156 mm. Smaller pitch means finer detail at the same viewing distance.

Does a phone need a higher PPI than a monitor?

Yes, because it is held closer, often 25 to 35 cm from the eye. Phones commonly exceed 400 PPI so that pixels stay invisible at that distance, while a monitor viewed from twice as far needs roughly half the density.

Can I use this for a TV or projector?

For a TV, yes: enter the native resolution and the diagonal in inches. For a projector, measure the diagonal of the projected image, since the density depends on how large you throw the picture.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 20). PPI Calculator. Tools Directory. Retrieved October 27, 2026, from https://tools.milunir.com/photography/image-size-and-print/ppi-calculator/

MLA

Tools Directory Editorial Team. “PPI Calculator.” Tools Directory, 20 Oct. 2026, https://tools.milunir.com/photography/image-size-and-print/ppi-calculator/. Accessed 27 Oct. 2026.

Chicago

Tools Directory Editorial Team. “PPI Calculator.” Tools Directory. Last modified October 20, 2026. Accessed October 27, 2026. https://tools.milunir.com/photography/image-size-and-print/ppi-calculator/.

Link<a href="https://tools.milunir.com/photography/image-size-and-print/ppi-calculator/">PPI Calculator – Tools Directory</a>