Compress an image to 100 KB: quality set automatically, nothing uploaded

Government e-services, university application portals, exam registrations, HR systems and older content management installs commonly cap a photo upload at 100 KB. The number dates from the early 2000s: a 100 KB JPEG sat comfortably in a database row, crossed a dial-up line in seconds, and was more than enough for the 200-pixel thumbnail printed on a badge or admission slip. The reasons faded but the limit stayed, and because a phone camera now writes 3–6 MB per shot, 'file too large' has become one of the most common dead ends on an online form.

The frustrating part is that most portals give no guidance: they reject the file and leave you to guess a quality number in some other app, upload, get rejected again, and repeat. This page removes the guessing. You set the ceiling, the converter searches for the setting that meets it, and you see the exact resulting size before you download anything.

How good a 100 KB JPEG looks depends on how many pixels it has to describe and on what is in the picture: flat areas and drawings compress far better than grainy photos. We have not measured real photographs, so we do not publish a quality-by-size table. What we have measured, on this site with the default 100 KB setting, is the two test files below (see the section on real runs for the byte counts).

The two rows above are synthetic test files, not photographs, so a real photo of the same size will land on a different quality. The tool does not rely on any table. Select 'Target size' next to the quality control and pick 100 KB (this page starts there). For each file the converter first tries quality 95; if that already fits, you keep it. Otherwise it tries quality 30. If that fits, it binary-searches the whole-number quality in between, seven encodes at most, and keeps the highest that fits. If even quality 30 is too big, the longest side is reduced by 10% and the search runs again, until the file fits.

Every attempt is a real encode measured in your browser, so the size in the results list is the size the portal will see, byte for byte. PNG has no quality setting, so in this mode PNG inputs are saved as JPG and transparent areas turn white. WebP stays WebP if you chose it and is 25–35% smaller than JPG at the same quality, but confirm that the portal accepts .webp before relying on it; many still list only JPG.

We ran this page on a 1600×1000 synthetic test pattern (not a photograph) saved as a 120,706-byte JPEG. At the default 100 KB target it kept the full 1600×1000 size and settled on quality 83, for a 96,532-byte result shown as "100 KB 이하 — 96,532바이트".

We then set a custom 10 KB target together with an exact custom pixel size of 1000×1000 (Keep proportions off). The exact pixel size was kept — it was never shrunk to chase the byte target — and quality dropped to 30, landing at 33,970 bytes with the on-screen message: "10 KB 이하로 줄이지 못했습니다. 가장 작게 만든 결과는 33,970바이트입니다." When a fixed pixel size and a byte target conflict, the pixel size wins and the shortfall is reported instead of resizing further.

We also ran the default 100 KB target on a second test file, a 1254×1254 pixel-art PNG (not a photo) of 436,475 bytes. Because PNG has no quality setting, it came out as a JPG at the same 1254×1254 size, quality 94, for a 95,261-byte result — under the 100 KB target. This run took about 7–10 seconds, versus 3–5 seconds for the other cases, since PNG inputs need an extra conversion step before the quality search can start. The runs were repeated and produced byte-identical output in the same browser; other browsers or encoders may differ.

Crop before you compress. An ID photo is usually 3:4 with the face filling the frame, so a 4000-pixel phone photo cropped to the head and shoulders is often under one megapixel before any quality is lost. Then set the Resize box to the dimensions the form actually wants; a common ID-photo field asks for something around 300 × 400 px, and at that size 100 KB allows quality 90 or better. The rule for print sizes is pixels = centimetres ÷ 2.54 × 300, so a 3.5 × 4.5 cm passport photo at 300 dpi is 413 × 531 px.

Compress once, from the original. Every JPEG save adds a little damage, so re-saving a file that has already been through a messaging app or an earlier compressor gives a worse result than starting from the camera file. And if the form allows it, 200 KB or 500 KB is a kinder ceiling than 100 KB for landscapes and group photos, where there is simply more detail to keep.