Which format compresses best?

For photographs, AVIF is usually smallest, WebP is close and far more widely supported for encoding, and JPEG is the most compatible. For flat graphics and screenshots, PNG or WebP will normally beat JPEG at any comparable quality.

Can I compress PNG files?

PNG is lossless, so there is no quality slider. Reduce PNG size by lowering the pixel dimensions or converting to WebP, which supports both transparency and lossy encoding.

Will compressing twice degrade the image?

Yes. Every lossy encode discards information permanently, and re-encoding an already-compressed file compounds it. Work from originals where you can.

Compress a folder of images at once

Set a quality level, convert format if it helps, and see the real size of every file after it is encoded.

Drop images here

JPG · PNG · WebP · AVIF · GIF · BMP

Processed on your device
Built for large batches
No account, no upload

Where the savings actually come from

Two things determine an image file's size: how many pixels it contains and how aggressively those pixels are encoded. Most oversized files on the web are oversized because of the first, not the second — a 4000-pixel-wide photo displayed in an 800-pixel column is carrying twenty-five times the pixel data it needs.

So the largest single win is usually resizing, not compressing. If you have not already capped your dimensions, turn resizing on and set a width that matches how the image is displayed. Compression then works on a sensible starting point instead of squeezing detail nobody will see.

Choosing a quality level

Quality values are not percentages of anything meaningful, and they are not comparable across formats — WebP at 75 and JPEG at 75 make different trade-offs. In practice, 85 is a safe default for photographs you care about, 75 is a good balance for the web, and 60 starts to show visible artefacts in smooth gradients like skies.

Flat graphics, screenshots and text behave differently: they suffer at low quality much sooner than photographs, and often compress better as PNG or WebP. If a compressed screenshot looks smeared around the lettering, that is the format choice talking, not the quality slider.

Why sizes appear only after processing

Predicting an encoded file size without encoding it is guesswork, because it depends on the content of the image as much as the settings. Rather than showing an estimate that will be wrong for half your batch, this tool reports the measured size of each file once it exists, along with the percentage change against the original.

Occasionally a file will come out larger — usually a flat graphic converted into a photographic format, or an already-compressed JPEG re-encoded at a higher quality than it started with. The results table shows this plainly instead of hiding it.

Questions

Which format compresses best?: For photographs, AVIF is usually smallest, WebP is close and far more widely supported for encoding, and JPEG is the most compatible. For flat graphics and screenshots, PNG or WebP will normally beat JPEG at any comparable quality.
Can I compress PNG files?: PNG is lossless, so there is no quality slider. Reduce PNG size by lowering the pixel dimensions or converting to WebP, which supports both transparency and lossy encoding.
Will compressing twice degrade the image?: Yes. Every lossy encode discards information permanently, and re-encoding an already-compressed file compounds it. Work from originals where you can.