Reading JAM’s range the right way round
IIT JAM’s brochure states the signature size as 80 × 280 to 160 × 560, written height × width — a convention that trips people up, because most image tools (this one included) describe dimensions as width × height. In width × height order, that same range is 280 × 80 up to 560 × 160. This page uses the upper end, 560 × 160, matching the same “default to the largest accepted size” reasoning as the JAM photo page: more source pixels for the same accepted file, no real downside as long as the byte size still fits.
If you see this page’s numbers and JAM’s brochure numbers side by side and they look transposed, that’s expected — width and height have simply swapped position, not the actual dimensions.
Getting a clean signature into range
50–150 KB is a comparatively generous band for a signature-sized image, wide enough that most reasonably clean scans or photos land inside it without much adjustment. The more common issue at this size is the opposite of the small IBPS fields: a signature photographed with visible paper texture, a shadow, or an off-white background can push past 150 KB before this tool even needs to try, simply because there’s more visual noise for the JPEG encoder to spend bits on.
A flatbed scan on plain white paper, cropped reasonably close to the signature itself before upload, gives this tool the cleanest source to work from and the most predictable result inside the 50–150 KB range — the same advice that applies to the IBPS signature field, just with more headroom here to work with.