What is Image DPI? – A Clear Explanation

DPI (dots per inch) is a measure of image resolution — specifically, how many pixels will be printed per inch of physical media. Understanding DPI helps you avoid common mistakes when preparing images for both screen and print.

DPI vs PPI: clarifying the terms

Strictly speaking:

• DPI (dots per inch): A print term — how many ink dots per inch a printer places on paper.
• PPI (pixels per inch): A screen term — how many pixels per inch a display shows.

In common usage, people say "DPI" when they mean both. This guide uses DPI in the common sense.

DPI for web images: it doesn't matter

This surprises many people: DPI has no effect on how an image looks on screen.

Screens display images based on pixel dimensions, not DPI. A 1200 × 800 px image displays at 1200 × 800 px on screen regardless of whether its DPI metadata says 72, 96, or 300.

Why? Because screens measure in pixels, not inches. The "DPI" stored in image metadata is only relevant when printing.

DPI for print: it matters a lot

When printing, DPI determines the print quality:

• 300 DPI: Standard for high-quality print (photos, brochures, business cards). Sharp details.
• 150 DPI: Acceptable for large format prints viewed from a distance (posters, banners).
• 72–96 DPI: Screen resolution — looks fine on screen, too low for print (appears pixelated).

Calculation: to print at 4 × 6 inches at 300 DPI, you need 1200 × 1800 px (4 × 300 = 1200, 6 × 300 = 1800).

How to calculate needed pixel dimensions for print

Formula: print size (inches) × DPI = required pixels

• 4 × 6 inch print at 300 DPI → 1200 × 1800 px minimum
• 8 × 10 inch print at 300 DPI → 2400 × 3000 px minimum
• 5 × 7 inch print at 300 DPI → 1500 × 2100 px minimum
• A4 (8.3 × 11.7 inch) at 300 DPI → 2490 × 3510 px minimum

Can you increase DPI to improve print quality?

No — and this is a common misconception. If a 800 × 600 px image has its DPI metadata changed from 72 to 300, the image doesn't gain new pixel data. The same 800 × 600 px will print at 800/300 = 2.67 × 2 inches (tiny). You can't create detail that doesn't exist by changing DPI.

To increase print quality, you need more actual pixels — either by photographing at higher resolution or (carefully) upscaling.

DPI in Resizo

Resizo focuses on pixel dimensions. For web use, just set your pixel dimensions and choose a format. For print: calculate the pixel dimensions you need first (print size × DPI), then resize to that.