DPI vs PPI: What Is the Difference?
PPI relates pixels to physical length; DPI relates printer dots to physical length. The terms are often blurred, but the distinction aids print setup.
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Comparison at a glance
DPI
PPI
Quick answer
PPI describes how many image pixels are assigned to an inch of physical display or print size. DPI describes printer dots per inch. People and software sometimes use the labels interchangeably, but separating source pixels from output dots prevents false assumptions about resolution.
| Criteria | PPI | DPI |
|---|---|---|
| Counted element | Image pixels | Printer dots |
| Typical use | Image placement or display density | Printer output capability or setting |
| Changes pixel count? | Not by metadata alone | No |
Calculate PPI at print size
Divide pixel width by intended print width in inches. A 2,400-pixel-wide image placed eight inches wide supplies 300 PPI. Place the same file sixteen inches wide and it supplies 150 PPI. No pixels disappeared; the physical placement changed their density.
The printer then represents those pixels using its dots, inks, and screening method. Several output dots may contribute to the reproduction of one source pixel, so a printer's DPI number is not a direct statement of distinct image pixels.
One image file, three print sizes
A fixed 1,800 × 1,200 pixel image demonstrates why PPI belongs to the image-plus- size relationship rather than to the file alone:
| Print size | Supplied pixel density | What changed |
|---|---|---|
| 6 × 4 in | 300 PPI | Pixels are packed most densely |
| 9 × 6 in | 200 PPI | Same pixels spread over a larger area |
| 12 × 8 in | 150 PPI | Same file, lower placement density |
Metadata trap
Changing a file's resolution metadata from “72” to “300” without resampling does not create new pixels. It can change the default physical size a program suggests, but the captured pixel dimensions remain the limiting inventory.
Why the vocabulary gets mixed
The Library of Congress notes that DPI originated with print dots while PPI is the more precise digital-image term, yet common usage often blurs them. When a service requests “300 DPI artwork,” confirm whether it actually wants 300 PPI at final dimensions and ask for required pixel dimensions.
Sources
- 1. What is DPI? — Adobe
- 2. What is PPI? — Adobe
- 3. Duplication Services Glossary — Library of Congress
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