How to compress an image to an exact file size
Most upload forms do not ask for a quality percentage — they ask for a file under a fixed number of kilobytes, and sometimes above a minimum too. This guide explains the three things that actually control file size, how to land on a target like 100 KB without guessing, and the photo-and-signature routine that exam portals expect. When you just want the result, the compress to an exact KB tool takes the number directly and finds the setting for you.
The three levers that set file size
A file's size in kilobytes comes from three things working together. Move any of them and the number changes — knowing which to move keeps the picture usable.
| Lever | Effect on size | Effect on the picture |
|---|---|---|
| Quality (compression level) | Large — the main dial for hitting a target | Lowers detail; invisible until pushed hard |
| Pixel dimensions | Large — half the width is roughly a quarter of the size | Smaller on screen, but full detail at that size |
| Format | Moderate — JPG and WebP beat PNG for photos | JPG/WebP are lossy; PNG is lossless |
For a hard target like 100 KB, quality is the dial you trim last and dimensions is the lever you pull first. A 4000-pixel phone photo squeezed to 100 KB looks worse than the same photo resized to 1000 pixels and then compressed to 100 KB, because the compressor has fewer pixels to spend the budget on.
Land on a target without guessing
Dragging a quality slider and re-checking the file size is slow. A target-size compressor works the other way round: you give it the number, and it searches for the quality that lands just under it.
| Target | Typical use | Approach |
|---|---|---|
| 100 KB | Many exam and job portals | Compress straight to 100 KB; resize first if it is a big photo |
| 50 KB | Photo slots on tighter forms | Resize to ~600–800 px, then compress to 50 KB |
| 20 KB | Strict photo limits | Resize to ~400–600 px, then compress to 20 KB |
| 10 KB | Signatures and thumbnails | Crop tight, drop to greyscale-like tones, compress to 10 KB |
Aim a little under the cap, not exactly on it — 96 KB on a 100 KB limit. Some portals re-encode your file on their side, which can nudge it back up over a target you hit precisely.
The exam-form photo and signature workflow
Indian exam portals (SSC, UPSC, NTA, IBPS and the rest) almost always want two files at once: a photo within one KB window and a signature within a smaller one, each at set dimensions. Treat them as two separate jobs.
- Read the notification for both the maximum and minimum KB, and the required pixels, for the photo and the signature separately.
- Resize each to the stated pixels first — for example a 200×230 photo and a 140×60 signature — then compress to the KB window.
- If a file drops under the minimum, pad it back up so it sits inside the range without changing how it looks.
- If the portal rejects the file for type, re-save it as a true JPEG — a renamed or HEIC file fails even at the right size.
Compressing many images to the same size
If you have a folder of images that all need to come in under the same limit — a set of product shots, a batch of documents — doing them one at a time is wasted effort.
The bulk image compressor applies one setting across the whole batch and returns them as a ZIP, all in your browser. For a precise per-file KB target on a few important images, the single compressor gives tighter control.
Frequently asked questions
Related guides
- Compress without losing quality
Lossy vs lossless, picking the right format, resizing first, and hitting an exact KB target, explained plainly.
- Shrink photos for email & chat
Fit attachment limits, send many images at once, and avoid WhatsApp re-compressing your photos to mush.
- Resize in cm or mm
The cm-to-pixel formula, what DPI to choose, a ready conversion table, and how to hit an exact print size.