Softonic

DPI PPI Calculator

Step 1 / 3 Pixels per inch
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Same image, three different conversations: the photographer asks about DPI for print, the UI designer asks about PPI for a Retina target, the printer shop needs the image in a specific pixel count. All three are the same math applied to different sides of the problem. This calculator handles the display side: enter the resolution and diagonal, and it returns the PPI plus the dot pitch in millimeters. For print, use the same division: pixel count divided by physical size in inches gives the DPI.

How to calculate PPI

  1. 1

    Enter the resolution

    Type the horizontal and vertical pixel counts of the display, for example 1920 x 1080.

  2. 2

    Enter the diagonal

    Type the physical diagonal of the screen in inches, for example 15.6.

  3. 3

    Read the density

    The tool returns the PPI plus the implied dot pitch in millimeters per pixel.

  4. 4

    The same math for print

    For print, divide the pixel count of the image by its physical size in inches to get the DPI.

DPI vs PPI, the short version

  • DPI (dots per inch) is a print measurement: how many ink dots per inch the printer lays down.
  • PPI (pixels per inch) is a display (and image) measurement: how many pixels per inch of physical screen (or printed image).

In photography workflows the two terms get swapped casually; for strict accuracy, say PPI when you mean image density and DPI when you mean printer output.

The formulas

PPI from display diagonal:

diagonal_pixels = sqrt(width_pixels^2 + height_pixels^2) PPI = diagonal_pixels / diagonal_inches

DPI for print from pixel count and physical size:

DPI_horizontal = width_pixels / width_inches

Both axes should match; when they do not, the image is non-square-pixel which causes distortion.

Density landmarks

Device type Typical PPI
Old desktop LCD (2005) 96
Retina iMac 5K 27“ 218
iPhone 15 Pro 6.1“ 460
Galaxy S24 Ultra 6.8“ 500
Print, magazine quality 300 DPI
Print, newspaper 150-200 DPI
Billboard 10-30 DPI (viewed from far)

Required pixels for print

To print an image at 300 DPI in a given physical size:

  • 4x6 inch print: 1,200 x 1,800 pixels
  • 8x10 inch print: 2,400 x 3,000 pixels
  • A4 (8.27x11.69 inch): 2,481 x 3,507 pixels
  • 16x20 inch poster: 4,800 x 6,000 pixels

Lower DPI tolerable for larger prints because viewing distance increases. A 24x36 inch poster viewed from 3 feet looks fine at 150 DPI.

Viewing distance matters

The eye can only resolve about 300 PPI at typical reading distance (25-30 cm). Hold the same screen at arm’s length and you no longer need more than 200 PPI for “retina” sharpness. That is why phones need higher PPI than monitors: phones live closer to your face.

Tips

  • Upscale carefully. Going from 72 to 300 PPI by resampling adds pixels but no detail. For large prints from small images, consider AI upscaling tools.
  • PPI is not in the JPEG. An exported JPEG at “72 DPI” or “300 DPI” is the same file with a metadata tag. Print shops use the tag to decide how large to print unless you specify size directly.
  • Check print provider specs. Billboards, decals and textiles each have their own DPI sweet spots; 300 DPI is overkill for most large-format jobs.

Frequently Asked Questions

On the web, DPI/PPI in the JPEG header is ignored; the browser renders the image at whatever pixel dimensions you specify in HTML/CSS. What matters is the pixel count. Export at the pixel dimensions your layout needs and ignore the DPI field.

Apple uses “Retina” as a marketing term for displays where individual pixels are not visible at normal viewing distance. The threshold depends on distance: around 220 PPI for a 27“ desktop, 326 PPI for a phone. Higher is always better; lower may be noticeably pixelated.

Only up to the scanner’s optical DPI. Interpolated DPI above the hardware maximum is software upscaling and adds no real detail. 600 DPI is plenty for most documents; 1200+ for fine art or archival.

No. Your inputs are not saved or stored. They are sent to our server to compute the results, and in the step-by-step mode they are added to the page link as you move between steps. Nothing else is done with them.

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