A full-size phone or camera photo will not go under 100 KB by lowering the quality alone. Our 18-megapixel test photo of the Golden Gate Bridge, 13.8 MB as it came, only fit once it had been shrunk to 1612 by 1008 pixels, about a tenth of its original pixels, at JPG quality 43. Every large photo we tried ended up in the same place: roughly 1.1 to 1.6 million pixels, at a quality in the low 40s.
So when an application form or upload portal says 100 KB, the real question is how many pixels you can keep. We measured that on 24 September 2026 with our Compress to a file size tool at its defaults: same format out as in, quality no higher than 92, and the picture made smaller only once quality has reached the lowest level we allow, 40 for JPG.
Six images, five size limits
| Image | Original | Under 50 KB | Under 100 KB | Under 200 KB | Under 500 KB | Under 1 MB |
|---|---|---|---|---|---|---|
| Golden Gate Bridge photo, 5388×3368 | 13.8 MB | 1096×685, q43 | 1612×1008, q43 | 2360×1475, q43 | 3973×2483, q43 | Full size, q58 |
| Waterfall photo, 3072×2048 | 2.95 MB | 875×583, q43 | 1285×856, q43 | 1901×1266, q43 | Full size, q51 | Full size, q80 |
| Photo of people, 2816×1536 | 3.42 MB | 1119×611, q40 | 1711×933, q42 | 2675×1459, q41 | Full size, q79 | Full size, q89 |
| Photo, 1408×768 | 806 KB | 1228×670, q40 | Full size, q71 | Full size, q89 | Full size, q92 | Full size, q92 |
| Portrait, 922×1152 | 647 KB | Full size, q55 | Full size, q81 | Full size, q92 | Full size, q92 | Full size, q92 |
| Homepage screenshot (PNG), 2880×1800 | 441 KB | 984×616, 192 colours | 1592×995, 128 colours | Full size, 128 colours | Full size | Full size |
Read the table by row and you can see where each photo stops fitting at full size. Under 1 MB, every image kept all its pixels. Under 500 KB, only the 18-megapixel photo had to shrink. At 100 KB, the three large photos lost 63 to 91% of their pixels, while the two that were already small kept their full size at a middling quality. Quality barely moved: 40 to 43 for every large photo. The pixel count, not the quality setting, is what a tight limit takes from you.
Our tool stops lowering quality at 40 and shrinks the picture from there, because we think a smaller, cleaner picture beats a full-size one saved at quality 15. If your form shows the photo small, as a thumbnail or an ID photo, 1200 pixels across is plenty and the trade costs you nothing you would see.
WebP doesn’t rescue a 100 KB limit
WebP is usually smaller than JPG at the same quality, so we expected it to keep more pixels under the same limit. On big photos it barely did. Under 100 KB, the Golden Gate photo came out 1647 pixels wide as WebP against 1612 as JPG, 2% more. The photo of people gained 1.4%. The waterfall came out narrower as WebP, 1159 pixels against 1285. We haven’t worked out why that one went backwards.
WebP did help the two small images, which fit at full size either way: it held quality 80 where JPG held 71, and 89 where JPG held 81. And a form that sets a size limit may not accept WebP at all. Our advice for a limit is to stay with JPG and let the pixels go; for a web page where you choose the format, see our AVIF, WebP and JPG measurements.
Screenshots are slower
PNG files take a different route: the tool first lowers the number of colours, which keeps text crisp, and shrinks the picture only when that isn’t enough. Our homepage screenshot fit under 200 KB at full size with 128 colours. Under 100 KB it had to shrink to 1592 pixels wide, and finding that size took 27 seconds on a fast laptop, against under 3 seconds for each photo. Switching the output to JPG or WebP is quicker, and the WebP copy kept 2599 pixels of width under the same limit.
One more thing happens on the way: the file loses its camera details and location, because a re-saved image starts with no metadata. If that matters to you, our guide to EXIF and GPS covers what else a photo carries.