PPI describes pixels in a digital image relative to a physical print size. DPI describes the dots a printer places on paper. The terms are often used interchangeably in upload instructions, but they describe different stages of the workflow.
| Term | Measures | Controlled by | Changes image detail? |
|---|---|---|---|
| PPI | Image pixels per printed inch | Pixel dimensions and print size | Only when pixels are resampled |
| DPI | Printer dots per physical inch | Printer, driver, ink, and paper | No |
| Metadata DPI | A stored physical-size instruction | Image editor or camera software | No |
Which number should you use?
When preparing an image, calculate PPI from the pixels available at the final physical size. When configuring a printer, use the printer's supported quality settings. If an application portal says “300 DPI,” it often expects 300 pixels per inch at the requested dimensions, so verify whether it also provides an exact pixel size.
Metadata change versus resampling
Changing metadata
A 3000-pixel image changed from 72 to 300 DPI keeps all 3000 pixels. Software may display a smaller default print size, but the digital detail is unchanged.
Resampling pixels
Resampling creates or removes pixels. Downsampling can discard detail; upsampling estimates new pixels but cannot recover detail that the source never captured.
A practical example
A 2400 × 3000 pixel photo printed at 8 × 10 inches provides 300 PPI in both directions. The same file printed at 16 × 20 inches provides 150 PPI. Its embedded metadata can say 72, 96, or 300 without changing those calculations.
What affects visible print quality
- Actual pixel detail, focus, noise, compression, and sharpening.
- Print size and normal viewing distance.
- Printer technology, paper, ink, and output settings.
- Whether the image has been enlarged beyond its useful resolution.