Resolution Converter

Print specs and screen specs use the same vocabulary to mean different things, and the resulting confusion is responsible for a lot of pixelated business cards. A printer asks for 300 DPI, you hand them a 1500-pixel image, and nobody's quite sure what size that prints at without doing the division.

This converter takes any two of three values — pixel dimensions, physical dimensions, and resolution — and computes the third. Switch between DPI (dots per inch, print) and PPI (pixels per inch, screen); the math is the same, but the labels matter to whoever's receiving the file. Useful for sanity-checking before sending art to print or before resizing a photo for a specific physical output.

The tool also reports whether your image has enough pixels for the intended print size at the requested resolution, which is the question most people are actually trying to answer.

What's actually happening when a printer "needs 300 DPI" is a calculation chain. The printer puts down ink dots at a fixed maximum density (often 1200 or 2400 hardware dots per inch). Each "pixel" in the source image is reproduced by a halftone cell of those hardware dots, and the cell needs enough dots to render gradients smoothly. The de-facto 300 PPI source resolution gives the print process roughly four hardware dots per source pixel in each direction, which is where the human eye stops noticing pixelation at typical reading distance.

Worked example: print a 6"×4" photo at 300 DPI. Required pixel dimensions = 6 × 300 by 4 × 300 = 1800 × 1200 pixels. Your phone camera shoots 4032 × 3024, so plenty of headroom. Now print the same shot as 16" × 24" wall art at 300 DPI — that needs 4800 × 7200 pixels, which the phone can't produce. You either drop to 200 DPI (acceptable for art viewed from across a room), upscale with AI, or shoot a higher-resolution source. The converter does this arithmetic both directions in seconds; the failure mode without it is "image looks fine on screen, prints pixelated".

Limits worth naming: the calculator assumes the input pixel dimensions are accurate. A photo metadata field claiming 4000 × 3000 pixels can hide upsampling — a 1000 × 750 original "enhanced" to 4000 × 3000 has the pixel count of a high-resolution image but the actual detail of a low-resolution one. Print at 300 DPI and the extra pixels don't help. To check, look at one corner of the image at 100% zoom and look for soft-edged blocks where sharp edges should be.

For screen rendering specifically, "pixel density" matters less than it did. CSS pixels are device-independent; a 1x phone screen and a 3x phone screen render the same CSS pixel size to the user, with the 3x screen using nine times the actual hardware pixels. For images, source 2x or 3x assets and let the browser pick via srcset. The PPI of the screen itself rarely needs to be in your math; the device-pixel-ratio (DPR) abstraction handles it.