DPI vs PPI: They're not the same
PPI (Pixels Per Inch) describes digital images โ how many pixels exist per inch on screen. DPI (Dots Per Inch) describes printing โ how many ink dots a printer places per inch on paper.
These terms are frequently confused because they both describe density. In practice:
- When you're working with digital images, you're dealing with PPI.
- When you're printing, both PPI (of the source image) and DPI (of the printer) matter.
Does DPI matter for digital uploads?
For screen-only use (websites, social media, exam portals), DPI/PPI is largely irrelevant. What matters is the pixel dimensions (e.g., 600ร600 px) and file size (e.g., 200KB).
A 600ร600 px image looks identical on screen whether it's saved at 72 PPI or 300 PPI. The PPI metadata doesn't change the actual number of pixels โ it only tells printers how to scale the image.
When uploading to portals like US Visa or US Passport, focus on pixel dimensions and KB size, not DPI.
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When DPI actually matters
DPI matters when you're printing. Standard print quality requires:
| Use case | Recommended PPI |
|---|---|
| Standard photo printing | 300 PPI |
| Magazine / professional printing | 300โ350 PPI |
| Large format posters | 150โ200 PPI |
| Billboard / very large prints | 72โ100 PPI |
How to check and change DPI
Most image editing tools show DPI in the image properties. To change it without altering the image:
- PhotoResizer.us: Use the Image Resizer โ set dimensions in pixels for digital use.
- Photoshop: Image โ Image Size โ uncheck Resample โ change Resolution.
- GIMP: Image โ Print Size โ change resolution.
Remember: changing DPI metadata without resampling doesn't add or remove pixels. It only changes how the image scales when printed.