What 200 and 300 DPI mean when a form asks for them

The arithmetic, once

Dots per inch is pixels divided by inches. A photograph 2000 pixels across, printed 10 inches wide, is 200 DPI. The same file printed 5 inches wide is 400 DPI, and stretched across 20 inches it is 100 DPI. Nothing about the file changed; only the paper did.

This is why “my scan is 300 DPI” is only half a statement. It is 300 DPI at some particular size, and putting it on a different sheet, or inside a different margin, changes the figure.

Working it out for your own document

1. Find the box the photograph will sit in. Subtract the margins from the sheet. A4 with a 10 mm margin leaves 190 by 277 millimetres, which is 7.48 by 10.91 inches.
2. Multiply by the resolution the form asked for. 7.48 inches at 200 DPI is 1496 pixels across. At 300 DPI it is 2244. That is the number your photograph has to reach.
3. Compare it with what the photograph actually has. The builder shows each photograph's pixel size beside the turn buttons on the Photos step. If it is above the figure you calculated, set the ceiling and stop; if it is below, no ceiling will help.
4. Set the ceiling and leave it. Choose 200 or 300 on the Quality step. The ceiling caps the resolution and never raises it, so a photograph that only carries 140 DPI across the page stays at 140 and the file stays small.

The figures for A4, already done

Any phone made in the last decade clears every number in that table by a wide margin, which is the reassuring part: the resolution requirement is almost never the problem. The size limit that comes with it usually is, and that has its own guide.

Where two to a sheet comes in

Resolution is pixels divided by inches, so halving the inches doubles the resolution for free. A photograph of an identity card that only manages 140 DPI across a full A4 page manages 280 DPI when two cards share the sheet, because each one is now half the width.

This is the move for small documents — cards, certificates, receipts, mark sheets — and it is why a form that wants 300 DPI is often satisfied by putting two documents on one page rather than by a better camera. It also halves the number of pages, which halves most of the file size.

Four numbers worth remembering

Every figure above the requirement is data that will be thrown away by a printer or a screen. Setting the ceiling is how you throw it away deliberately, on the way into the document, instead of leaving it in the file for a portal to reject.