Sensor MP to Print Size DPI

Sensor Megapixels vs Print DPI

The DPI of a printed photo is just the pixel count along one edge divided by how many inches that edge spans on paper: DPI = pixels ÷ inches. Starting from total megapixels, each side comes out as side_pixels = √(MP × 10⁶ × aspect_ratio), and you then divide that by the paper width or height in inches (1 inch = 2.54 cm).

For photo prints you usually want at least 300 DPI. A 12 MP file (4000×3000) stays sharp up to 13×19″ and clears A3 (~30×42 cm) with room to spare. Drop to A4 (~20×30 cm) and roughly 6 MP already hits 300 DPI. Billboards and big posters that people see from several meters off get by on just 50–100 DPI, since how sharp something looks depends on how far away you are.

Applications

Photographers, designers, marketing teams and print shops lean on this either to pick a camera or to figure out how large they can safely print a file they already have. It is the same math behind upscaling calls in Photoshop, Lightroom or AI-based super-resolution.

FAQ

How many MP do I need for A3 at 300 DPI? About 12 MP at a 3:2 aspect ratio. That gives you close to 4000×6000 px, which maps neatly onto A3 dimensions.

Is 300 DPI always required? No. It is the benchmark for photo books and magazines, yet newspapers run at 150–200 DPI and posters often sit around 100–150 DPI.

Why do billboards work at 50 DPI? From 10–30 m away the eye simply cannot pick out finer detail, and the DPI you need falls off as the viewing distance grows.