DPI (Dots Per Inch)
A measure of image resolution — the number of pixels or printed dots per inch. Higher DPI means more detail and larger file sizes.
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What Is DPI?
DPI (Dots Per Inch) measures the resolution of a digital image or print output — how many pixels or ink dots are packed into each inch. Higher DPI means more detail per inch, sharper output, and larger file sizes.
DPI for Screen vs Print
| Use Case | Recommended DPI | Reason |
|---|---|---|
| Web / screen display | 72–96 DPI | Screens typically display at 96 PPI; higher DPI is wasted |
| Email attachments | 96–150 DPI | Balance between quality and file size |
| Standard printing | 150–200 DPI | Sufficient for most documents |
| High-quality printing | 300 DPI | The professional print standard; laser printers use 600–1200 DPI |
| Large-format printing | 150–300 DPI | Billboard images are often as low as 30–50 DPI |
DPI and File Size
A 1 inch × 1 inch image at different DPIs:
| DPI | Pixel Count | File Size (PNG) |
|---|---|---|
| 72 | 72 × 72 = 5,184 px | ~15 KB |
| 150 | 150 × 150 = 22,500 px | ~65 KB |
| 300 | 300 × 300 = 90,000 px | ~260 KB |
Doubling DPI quadruples the pixel count and file size.
DPI in PDFs
A PDF has no inherent DPI — it is a vector document with physical page dimensions. DPI only matters when:
- Converting PDF to image — you must choose a DPI for the output image
- Scanning to PDF — the scanner captures at a chosen DPI and embeds the scan as a rasterised image inside the PDF
When compressing a PDF, reducing the embedded image DPI from 300 to 150 can cut file size by 50–75% with minimal visible impact on screen.