DEV Community

Robert Wallace
Robert Wallace

Posted on

How to Calculate DPI for Print Design (And Why 72 PPI Is the Wrong Default)

#webdev #design #beginners #tooling

If you've ever designed something for print and had it come out blurry or the wrong size, the culprit is almost always one thing: wrong DPI assumptions.

Most designers start with the screen default — 72 or 96 pixels per inch — and treat it like a universal constant. It's not. That number only describes your monitor. Print, photo exports, and physical mockups have completely different requirements.

The basic math

DPI / PPI is just a ratio:

DPI = pixel count / physical size in inches
Enter fullscreen mode Exit fullscreen mode

So if you have a 3000×4000 pixel image and you want to print it at 10×13.3 inches, the math is:

  • Width: 3000 / 10 = 300 DPI
  • Height: 4000 / 13.3 = 300 DPI

That's the sweet spot for most offset printing. Below 250 DPI and you'll start seeing softness on coated stock. Above 350 DPI is usually unnecessary and just bloats file size.

When 300 DPI isn't the answer

  • Billboards / large format: viewed from far away, 30–75 DPI is fine
  • Web / social: 72–150 PPI is plenty because screens are fixed-pixel devices
  • Retina / high-DPI screens: CSS reference pixel is 96, but the device may have 2× or 3× physical pixel density

The mistake is treating "print DPI" and "screen PPI" as the same number. They aren't.

Why designers get this wrong

Three common traps:

  1. Resampling in Photoshop without checking actual dimensions — changing the DPI metadata doesn't add real detail.
  2. Exporting at 72 PPI from Figma/Sketch — the artboard size in pixels is what matters, not the PPI label.
  3. Ignoring bleed and trim — a standard US letter page with 0.125" bleed needs the file to be oversized before imposition.

The faster way to check

Instead of doing mental math, calculate the actual pixel density from the physical dimensions and native resolution. For a 27-inch 1440p monitor:

2560 / (27" × √(16/9)) ≈ 109 PPI
Enter fullscreen mode Exit fullscreen mode

That tells you whether text will look sharp at arm's length — it's not a print spec, it's a viewing-distance spec.

A practical check before you export

Before sending a file to press or framing a photo:

  1. Note the source pixel dimensions
  2. Note the target physical size
  3. Divide
  4. Compare to the target medium's recommended density

If you're designing for multiple outputs — web, Instagram, and a 16×20 print — each needs its own crop/resample pass. One file rarely fits all destinations.

I build lightweight browser-based dev tools at utilitylab.dev. If you want a fast client-side DPI/PPI check without installing anything, there's one there.

Top comments (0)