Guide
DPI vs PPI: what's the difference?
Both measure how many units fit into one inch. Which one applies depends on whether you are talking about a screen or image (pixels) or a printer (dots).
The short answer
PPI (pixels per inch) describes how densely pixels are packed on a screen or in an image.DPI (dots per inch) describes how many ink dots a printer lays down per inch. In everyday use people mix the two, and for converting a physical size into pixels the arithmetic is identical:
pixels = inches × PPI and inches = pixels ÷ PPI
If you only need a number, the inches to pixels converter does the multiplication and the pixels to inches converter does the division.
Why a pixel has no fixed size
A pixel is a unit of image data, not a length. It only becomes a physical size when you decide how many of them share an inch. The same 3,000 pixel wide photo is 10 inches wide at 300 PPI and 20 inches wide at 150 PPI. The image itself did not change; only how far it is stretched.
That also means the DPI value stored in an image file's metadata does not add or remove pixels. It is only a suggestion for the print size. Changing it without resampling leaves the pixel dimensions exactly as they were.
How to check whether an image is big enough to print
Divide the image's pixel width by the width you want to print, in inches. The result is the effective PPI.
- 3,000 px wide printed 10 inches wide: 3,000 ÷ 10 = 300 PPI, a sharp print.
- 3,000 px wide printed 20 inches wide: 3,000 ÷ 20 = 150 PPI, acceptable from a distance, softer up close.
Upscaling a small image in software makes the file larger but cannot add detail that was never captured. If the effective PPI is too low, a larger source image is the fix.
Which value should you use?
These are common conventions rather than fixed rules. If your printer or platform publishes its own requirements, follow those.
| Use | DPI / PPI | Note |
|---|---|---|
| Web pages and on-screen graphics | 96 | CSS defines 1 inch as 96 pixels. |
| PDF and PostScript page sizes | 72 | One point is 1/72 inch. |
| Draft prints and proofs | 150 | Quick checks; softer up close. |
| Standard photo and document printing | 300 | The usual target for sharp results. |
| Fine line art and very small text | 600 | Only if your printer asks for it. |
Screens, CSS pixels and device pixels
On the web, CSS fixes 1 inch at 96 CSS pixels, and 1 CSS pixel equals 0.75 point. Modern phones and laptops often pack two or three physical pixels into each CSS pixel, so a CSS inch on screen is not always a real inch. For measuring physical size, trust the print dimensions; for screen layouts, work in CSS pixels.
Common mistakes
- Designing a print file at 72 DPI and expecting it to look sharp on paper.
- Changing the DPI field in an editor without resampling and assuming the image got better.
- Forgetting bleed. Printers often need artwork to extend past the trim edge.
- Comparing screen size in pixels with print size in inches without a DPI in between.
Pixel sizes for common print jobs
These pages work out the pixel dimensions, bleed and cropping for sizes people ask about most: