Three levers, in the order that works
A size limit is never about compression alone. Most oversized documents are oversized because they carry pixels no sheet of paper could ever show, and throwing quality at that problem makes an ugly file that is still too big.
- The resolution ceiling. A 12-megapixel phone photograph placed on A4 is delivering around 500 dots per inch. Nothing prints that, and no screen shows it. Capping at 200 throws away three quarters of the data before quality is touched at all.
- Grey pages. A photographed form is black ink on white paper with a colour cast from the room light. Removing the colour usually takes another 40 to 50 per cent and costs nothing anybody will notice.
- The quality search. Only now does the size figure earn its place. The document is written, its real size measured, and then only the heaviest pages are re-encoded, aimed from that measurement — up to five passes, then it stops and says where it got to.
There is a fourth lever that is not compression at all: two or four photographs to a sheet. Halving the page count halves most of the file, and for a set of small documents it often reads better than one photograph rattling around on each sheet.
What the common figures mean in practice
| Figure asked for | Usually reachable with |
|---|---|
| 5 MB | Nothing to do — most documents are already under it at 300 DPI. |
| 2 MB | A 300 DPI ceiling for a short document, or 200 DPI for twenty pages or so. |
| 1 MB | A 200 DPI ceiling, colour kept, ten to fifteen pages. |
| 500 KB | A 150 DPI ceiling, or 200 with grey pages. |
| 200 KB | 150 DPI and grey, for up to about five pages. |
| 100 KB | Grey, 150 DPI and one or two pages. Beyond that, expect to be told the closest. |
| 50 KB | One page in grey at 150 DPI or lower — a single certificate or ID side. |
The full reasoning, including when to give up and send fewer pages, is in the guide on getting under 200 KB.
Questions about size limits
The portal says less than 500 KB. Where do I type that?
The Quality step, in the size field, which this page opens with. 500 KB is one of the buttons; anything else can be typed, and 480kb, 0.5 MB and 500000 are all understood.
Why did it stop above my figure?
Because going further would have taken the writing with it. The tool lowers quality in measured steps and stops at the point where a photographed form stops being legible, then tells you the closest size it reached. Grey pages, a lower resolution ceiling, or splitting the set across two documents are the three things left.
Does the figure count the whole document or one page?
The whole file, as the operating system will report it. That is what an upload box measures, so it is what this measures.
The size shown changed after I saved. Which one was right?
The one after saving. Before that the figure is measured on a sample of the pages and scaled, which is close but not exact; once the document has actually been written, the number shown is the file itself.