Use Target file size to aim for 100 KB, 200 KB, 500 KB or your own limit. The tool measures each encoded result against the limit. A target is a maximum byte size, not a guarantee that every image can fit without losing detail.
Compress an image below 100 KB
- Choose the format accepted by your upload destination.
- Select 100 KB under Target file size, or choose Custom limit and enter a whole number.
- Leave Allow smaller dimensions unchecked when you must preserve width and height. Otherwise enable it to allow further downsizing if quality changes are not enough.
- Process the image. The quality slider sets the highest quality to try for JPG/WebP; the search can go down to 10%.
- Check Target met or Above target beside the result. The exact byte count is displayed. Download and inspect the image at full size.
What the limit means
Target mode uses decimal KB: 100 KB means 100,000 bytes. General size labels elsewhere in the tool use 1,024-byte units, so the exact target byte counter is the clearest comparison. Each image has its own limit; a ZIP adds archive overhead.
How quality and dimensions are searched
The tool tries the chosen maximum quality, then a low-quality candidate. When the limit is reachable at the current dimensions, a bounded binary search refines the quality. If needed and explicitly allowed, it reduces dimensions and searches again, always drawing from the selected source. PNG ignores quality and requires downsizing for this additional search. Exact dimensions selected in Image Resizer are preserved.
If the result stays above target
The tool returns its smallest tested candidate and clearly marks the missed limit. Try a different permitted format, allow smaller dimensions or use a less demanding target. Do not upload a file labelled Above target to a form with that strict limit.
Check readability
Lower quality can damage fine text, gradients and edges. Smaller dimensions remove spatial detail. Keep the original and never assume that a byte-limit success also means acceptable visual quality.
Behind the result
Target mode checks actual encoded bytes against your limit. Quality is searched first; further downsizing requires your permission. A missed limit is reported explicitly.
What does encoding mean?
Decoding turns the bytes in an image file into pixels that a browser can display. Encoding turns pixels back into a file, using the rules of JPG, PNG or WebP. It is not encryption. Our compression and conversion tools decode locally, draw the image onto a canvas and call the browser’s canvas.toBlob encoder. The browser supplies the codec, so results can vary between browsers.
How JPG compression works
JPEG commonly splits image information into small blocks, uses a discrete cosine transform to describe patterns within them, then rounds transform coefficients in a step called quantization. Coarser rounding saves space but discards detail. The remaining values are efficiently coded into bytes. Our quality control is passed to the browser encoder; it is not a percentage of original detail retained or a guaranteed percentage reduction. Repeated JPG re-encoding can introduce additional artefacts.
How PNG encoding works
PNG uses reversible filters on pixel rows followed by DEFLATE compression. These steps can represent the encoded pixels without JPEG-style quality loss. PNG ignores the quality slider. This tool uses the browser’s PNG encoder, rather than a dedicated palette-reduction optimiser, so an already efficient PNG may not get smaller. Resizing or colour handling before encoding can still change pixels; lossless encoding does not promise that the whole editing pipeline preserves the original file.
How WebP compression works
Lossy WebP predicts image regions from neighbouring pixels, transforms the difference and quantizes it before coding the result. The format also supports a separate lossless mode, but this tool requests browser WebP encoding with a quality setting and does not expose a guaranteed lossless mode. Transparency can be retained. A lower quality setting often reduces size, although sharp text and fine textures may suffer.
Why the original may be kept
After encoding, the tool compares byte sizes. With Preserve supported metadata selected, when format, dimensions and geometry are unchanged and the new file is not smaller, it keeps the original bytes. This avoids a larger replacement. A retained original also retains its metadata: use the Metadata Remover when privacy cleaning is the goal. ZIP download bundles the files without another lossy image-encoding step.
Where processing happens
Your selected image is processed on your device, without an image upload. Canvas exports are new files and may change embedded metadata or colour information. Keep a master copy for archival work. Animated PNG and animated WebP are rejected; these tools handle static images.
How target-size compression works
Choose 100 KB, 200 KB, 500 KB or a custom decimal-KB limit. For JPG/WebP, the tool tries quality values from your selected maximum down to 10% and refines a successful bracket with a bounded binary search. When you explicitly allow smaller dimensions, it can also try up to eight downsizing steps. PNG ignores quality. Exact resizer dimensions are preserved. Only a measured output within the byte limit is marked Target met; otherwise the smallest tested candidate is marked Above target. This is a bounded search, not proof of a globally optimal result.
Metadata choice
Preserve supported metadata is the default: EXIF dates, camera and GPS fields are copied, with orientation reset after decoding and dimensions updated. PNG text/dates and JPG comments stay within their format. XMP, IPTC and original colour profiles are not transferred; embedded preview links are cleared. Retained metadata is included in target-size measurements. Remove metadata omits source metadata and disables the original-file fallback. Filesystem download dates are separate.
Explore the details: Browser encodingImage formats — MDN