Compress an image below an upload limit: bytes, format and dimensions
Translate the byte limit correctly, choose a supported output format and inspect the compressed download before uploading it.
Read all of the destination requirements
A failed upload may involve more than file size. Record the accepted formats, maximum bytes, minimum or maximum pixel dimensions and whether transparency is required. Keep an untouched original image so you can restart if compression removes an important detail. A document portal might reject a small WebP file because it accepts JPEG only; a profile image might need a particular shape regardless of its byte count. The compressor changes an image, but it cannot discover or enforce requirements that you have not supplied. Start with the destination’s actual instructions and error message.
Translate the cap into the tool’s units
This compressor explicitly uses 1 KB = 1,024 bytes in its target field. The data-size converter distinguishes decimal kB from binary KiB. If a destination gives a strict 100,000-byte cap, enter 100000 bytes in the converter and choose KiB: the result is 97.65625. That is the corresponding number for this compressor’s target field. Entering 100 there instead allows up to 102,400 bytes, which exceeds the original cap. When the destination says only KB, check its documented definition or actual rejection behavior rather than assuming both systems use the same convention.
| Destination limit | Bytes | Compressor target |
|---|---|---|
| 100 decimal kB | 100,000 | 97.65625 (units of 1,024 bytes) |
| 100 binary KiB | 102,400 | 100 |
Check the destination’s byte convention and formats. Measure the download instead of trusting a quality setting.
Choose the output format before tuning quality
The tool accepts supported JPEG, PNG or WebP source files and produces JPEG or WebP. JPEG output turns transparent regions white. WebP can retain transparency where the browser supports the encoder, but the destination must accept that format. Choose based on the receiving requirement, not the filename you want. This is lossy processing and animated input becomes a single frame. If retaining animation, metadata or a transparent background is essential to your task, check whether the offered workflow fits before spending time reducing a quality setting.
Use dimensions to control the amount of detail
Set a maximum width or height appropriate for the destination. The compressor keeps the aspect ratio and does not enlarge a small image. For example, fitting a 1,200 by 800 pixel source inside a 600 pixel maximum side gives 600 by 400 pixels. That is a geometric calculation, not a prediction of the output bytes. A smaller image has fewer pixels available to preserve detail, which may matter for small text or a diagram. The tool can reduce dimensions further when necessary to meet the selected file-size target, so read the actual output dimensions afterward.
Let measured bytes decide whether the target is met
The compressor tries browser-encoded output and measures its actual byte size. It searches quality settings and, when needed, reduces dimensions rather than assuming a quality percentage corresponds to a particular file size. MDN documents browser canvas encoding and Blob size in bytes. Browser encoders can produce different outputs from the same input, so a tutorial should not promise a universal final size. The generated sample lets you explore the process without selecting a file. Its 40 KB target corresponds to 40,960 bytes; the actual resulting size and dimensions are reported after that run.
Inspect legibility instead of trusting the quality number
Open the compressed preview and examine the parts the recipient needs: fine text, labels, faces or edges. The encoder quality percentage is a browser setting, not a measured perceptual-quality score. A target can be met while a necessary detail becomes difficult to read. Compare with the original at a sensible viewing size, then download and inspect the actual output if the task depends on it. If the result is inadequate, try a less restrictive target where the destination permits it, or reconsider the crop and source image before repeatedly lowering quality.
Verify the downloaded file at the destination
Check the downloaded file’s extension, bytes and dimensions, then upload that file rather than accidentally choosing the original. If the destination still rejects it, compare its exact requirement with the actual output. Some systems apply additional checks unrelated to size. A target-meeting preview cannot certify that the destination will accept the file. Keep a small margin below a strict cap when its comparison or display is unclear, and record the successful settings for later uploads. Avoid repeated recompression of already compressed downloads when you can return to the original source.
Keep local processing and image requirements distinct
The current compressor processes image data locally in the browser and does not upload your source image. That is separate from what happens when you later submit the download to another website. It also does not copy source metadata, which may affect workflows that depend on that information. Supported source limits include 25 MB, sixteen million pixels and 8,192 pixels per side; very large files may need a different preparation workflow. Save the original, chosen byte convention, format and dimensions together. This turns a one-off successful upload into a repeatable process with understandable tradeoffs.