Image Compressor

Large photos slow pages down and fill up inboxes. This tool re-encodes your images at a lower quality and, if you wish, a smaller width, and shows the size before and after so you can judge the trade-off.

Everything happens in your browser. The images are not uploaded to a server, and nothing is stored once you leave the page.

How image compressor works

Choose an output format, a quality from 30 to 95 and an optional maximum width, then drop images onto the box or choose them. Each result shows the original size, the new size, the percentage saved and the new pixel dimensions, with a Download button.

Both output formats are lossy: they discard detail the eye is least likely to notice. Lower quality gives a smaller file and more visible artefacts. WebP is usually smaller than JPEG at similar visual quality and is supported by current browsers, while JPEG works everywhere. JPEG has no transparency, so transparent areas are filled with white.

Reducing the width has the largest effect. File size roughly follows the number of pixels, so halving the width leaves about a quarter of them. If a result comes out larger than the original, the tool says so, which can happen with images that were already well compressed.

The formula

Pixels  =  width × height
Space saved  =  (original size − new size) ÷ original size × 100

Scaling an image by a factor k in width and height multiplies the number of pixels by k².

Worked example: resizing a phone photo

A 4000 × 3000 photo has 12 million pixels. Scaling it to 1920 pixels wide gives 1920 × 1440, which is about 2.76 million pixels, or 23% of the original.

Before any change to quality, the amount of image data is already less than a quarter of what it was. That is why choosing a smaller maximum width usually saves more than lowering quality.