A4, US Letter or original image size

A4 is 210 × 297 mm and US Letter is 8.5 × 11 in (215.9 × 279.4 mm). A4 is taller and slightly narrower, so an image that fits one exactly will not fit the other without a little scaling or a slightly different margin.

Choose the size your recipient will print on or expects to see. Neither is more correct in general, and both are supported at any orientation.

With automatic orientation, a wide image produces a landscape page and a tall image produces a portrait page. Forcing portrait or landscape keeps every page the same way up, which is what you want for a document that will be read as a set.

This option builds each page from the image itself: the PNG's declared physical resolution is used when present, otherwise 96 PPI is assumed. A 1920 × 1080 screenshot becomes a page of about 508 × 286 mm at the fallback value, which is larger than A4 — that is expected, not a bug.

Increasing the PPI after the fact does not add detail. It only changes how large the same pixels are drawn.

None, small (6.35 mm), comfortable (12.7 mm) and a custom millimetre value are available. Fit keeps the whole image visible inside the margins and preserves its aspect ratio, so nothing is stretched. Crop to fill covers the page area instead and trims the overflow, which is visible in the preview before you convert.

For documents meant to be read on screen or printed at home, A4 or Letter with small margins and fit placement is a safe starting point. Use original size when the physical dimensions of the images themselves matter, such as scans or labels.