How it gets under your target
A file's size depends on two things: how many pixels it has and how hard each one is compressed. Most tools only turn the quality down, which is how a photo ends up blocky and smeared. This one works in a fixed order:
- Full size first. It looks for the highest JPEG quality (up to 95) at which the photo, at its original dimensions, fits under your target.
- Pixels before quality. If fitting at full size would mean going below quality 40, or the result would score below 0.95 on a similarity measure (SSIM) against the original, it keeps the quality and reduces the dimensions instead — searching for the largest size that still fits.
- Only then lower the bar. If no size passes that bar, it allows lower quality, down to 10.
- Say so if it can't. If not even a tiny version fits, it tells you, and shows how close the smallest attempt came. If it fits only by shrinking below about 320 pixels on the long side, it warns that the photo may no longer be recognisable. Either way you see it before you download.
The result is the largest file under your limit that the search found — usually within a few percent of it — because a file far below the limit has given away quality you were allowed to keep.
What the quality verdict means
After compressing, the tool compares the result with the original at the result's size and turns the score into a word: Excellent (SSIM 0.98 or more), Good (0.95), Fair (0.90) or Poor. It measures compression damage — blur, blocks, banding. It does not count pixels given up, so read it together with the new dimensions shown beside it: “Excellent at 800 × 600” is a sharp small photo, not a sharp large one.
KB, kB and KiB
The tool counts 1 KB as 1,000 bytes. A file under 50 KB by that count is also under 50 KB on a site that counts 1 KB as 1,024 bytes, so it passes either way. If a form says MB, multiply by 1,000: 2 MB is 2,000 KB.
Why the result is always a JPEG
Hitting a size means trading some quality for bytes, and JPEG is the format every form, portal and email program accepts that can make that trade. PNG and the WebP this site makes are lossless, so they can only get smaller by losing pixels. If you need a PNG at a certain size, use the resizer to reduce the dimensions and save as PNG.
Getting a better result at a small size
- Crop first. Every pixel of background costs bytes. A head-and-shoulders crop leaves more of the budget for the face.
- Plain backgrounds are cheap. A light, even wall compresses far better than trees, gravel or a patterned shirt.
- Check required dimensions. If a form wants exact pixels as well as a size, resize to those pixels first, then compress — otherwise the tool may choose different dimensions.
- Use the longest-side limit above when you know the photo only ever needs to be, say, 1,200 pixels wide. It also makes the search faster.
Common targets
Each has its own page with notes on what usually asks for it: 20 KB (signatures and small ID photos), 50 KB (application forms), 100 KB (profile photos, document uploads) and 200 KB (web images, detailed scans).
Formats it reads
JPEG, PNG, WebP, GIF (the first frame) and BMP in any modern browser. HEIC — the iPhone's default — opens where the browser can read it, which today means Safari; elsewhere the page says so. AVIF works the same way. The finished JPEG carries no EXIF data, so it doesn't reveal where the photo was taken; a colour profile is kept so colours stay right.