Practical guide · November 8, 2026
PPI and DPI describe different grids
Use pixels per inch for image-size calculations.
Begin with the image grid
A raster image has a fixed number of pixels across and down. Dividing 3600 pixels by 300 pixels per inch gives 12 inches. The calculation describes the relationship between the source image and its intended physical size. It does not depend on the printer's advertised ink-dot resolution.
The printer has its own grid
Printer DPI describes dots of ink or toner placed per inch. Multiple dots can contribute to reproducing one image pixel. A printer advertised at 1200 DPI therefore does not mean every photo should be supplied at 1200 PPI. Ask the printer for the image resolution it expects.
A metadata tag adds no detail
Changing only a resolution tag from 72 to 300 does not add pixels. An 1800-pixel-wide image corresponds to 6 inches at 300 PPI or 12 inches at 150 PPI. In either case, the source still has 1800 pixels across. Resampling is a separate operation; this tool does not perform it.
Check the whole delivery specification
Ask for physical dimensions, resolution, bleed, color profile and file format before preparing a paid print job. This utility answers only the resolution-to-size question. It does not verify color, compression, focus, printer calibration or the visual suitability of an image. Review an actual print proof when the result matters.