Editor › Learn › PPI vs DPI: Resolution for Print Without the Confusion
What is the difference between PPI and DPI, and what resolution do I need for print?
PPI (pixels per inch) describes how densely your image's pixels are laid onto a physical print size; DPI (dots per inch) describes how the printing device builds tones from ink dots. They are different layers: one file property, one hardware property. For commercial offset work at reading distance, 300 PPI at final size is the safe standard because it comfortably exceeds what a 150 lpi halftone screen can use; large-format work viewed from further away needs far less.
Three numbers people conflate
| Term | What it measures | Where it lives |
|---|---|---|
| PPI | image pixels per printed inch | your file (pixels ÷ physical size) |
| DPI | device dots per inch | the printer / imagesetter |
| LPI | halftone lines per inch | the screening of a press |
Where "300 PPI" comes from
Offset presses reproduce tones through halftone screens, commonly around 150 lines per inch for quality commercial work. A long-standing prepress rule holds that the image should supply roughly 1.5–2 pixels per halftone line — 225–300 PPI at 150 lpi. 300 PPI is simply the comfortable top of that range, which is why it became the universal ask. It is a per-JOB number: newsprint screens coarser and needs less; fine art inkjet can use a little more.
Viewing distance changes everything
- Magazine page at 30 cm: 300 PPI.
- Poster at 1–2 m: 150 PPI is typically indistinguishable.
- Trade-show banner at 3 m+: 75–100 PPI prints perfectly acceptably.
- Billboard: often under 30 PPI. Nobody reads a billboard with a loupe.
Why upsampling does not fix a small image
Resampling to 300 PPI invents pixels by interpolation; it raises the number without adding detail, and aggressive upsampling adds softness or artifacts the press will faithfully reproduce. The honest fixes are: print smaller, accept the lower effective resolution given the viewing distance, or go back to a larger source. Changing the PPI value WITHOUT resampling, by contrast, is free — it only re-declares the physical size of the same pixels.
Checking a file quickly
Divide pixel dimensions by intended print size: a 3000×2400 px image printed at 10×8 in is exactly 300 PPI; at 20×16 in it is 150 PPI — fine for a wall print, marginal for a brochure. PhotoAIA's Image Size dialog does this arithmetic with resampling on or off, and its status bar shows document dimensions and DPI at all times.
Questions
- My printer asked for 300 DPI — do they mean PPI?
- Almost always yes. In everyday print communication "DPI" is used loosely for image resolution; supply 300 pixels per inch at final size and everyone is happy.
- Does the PPI number in the file matter for screens?
- No. Screens display pixels; a 1000-pixel-wide image renders identically at 72 or 300 PPI. The value matters only when translating pixels to physical print dimensions.
- What about vector artwork?
- Vectors are resolution-independent — they rasterise at output. Resolution questions apply to the raster images placed WITHIN artwork.