Resize and compress image

Resizing and compressing images without guesswork

“Make this image smaller” can mean two different things, and confusing them is why downloads sometimes come out larger than expected. This guide separates the two ideas — pixel dimensions and file weight — and explains how to hit a target with the resizer instead of trial and error. For a step-by-step walkthrough with target sizes, see how to resize an image for the web.

Dimensions versus file size

Dimensions are how many pixels wide and tall the image is, for example 4000×3000. File size is how many kilobytes or megabytes the file occupies on disk. They are related but not the same: a photo can have huge dimensions yet a modest file size, or small dimensions yet a heavy file if it is stored at maximum quality. Reducing dimensions almost always reduces file size, but you can also shrink the file at the same dimensions by lowering the export quality. Knowing which one a destination actually limits — a width in pixels, or a maximum file size — tells you which lever to pull.

How to reach a smaller file

For the web, work in this order: first set the dimensions you really need — a blog image rarely needs to be wider than the column it sits in, and a thumbnail needs far less — then lower the JPEG or WebP quality until the preview still looks good. Dropping a 4000-pixel-wide photo to 1200 pixels typically does most of the work, and a quality setting a little below maximum removes detail your eyes will not miss. The resizer keeps the original aspect ratio, so the image is never stretched or squashed; it does not crop, batch process, or target an exact file size for you, so you steer size by adjusting dimensions and quality.

Why a resized file can look bigger than you expected

Exporting re-encodes the image, and that is worth understanding. Choosing PNG output produces a lossless file, so the quality slider has no effect and photos can end up surprisingly large; PNG is the right pick for screenshots, graphics, and anything with transparency, not for photographs. Choosing JPEG or WebP re-compresses the image at the quality you set. If you reopen a file that was already heavily compressed and export it at full quality, the new file can be larger than the one you started with, because high quality means “re-encode with little compression,” not “match the original.” When in doubt, prefer WebP for the web and keep quality just high enough to look clean.

Sensible target sizes to aim for

If you are not sure what dimensions to use, a few rough targets cover most needs. Full-width web images rarely need to be wider than about 1600–2000 pixels; an image sitting inside an article column is fine around 1000–1200 pixels wide. Thumbnails and avatars usually live between 150 and 400 pixels. Email attachments are friendliest under a couple of megabytes, so resizing the dimensions down first is the quickest way to get there. Marketplaces and social platforms publish their own recommended sizes, so when a destination states a number, match it rather than guessing — uploading something far larger just gets re-compressed on their end anyway.

Everything happens in your browser

The image is resized locally with your browser's image and Canvas APIs and is not uploaded to a PixTools server. If a preview or download fails, try a smaller source file, switch the output to JPEG or PNG, or refresh in a current browser. When you instead need a bigger copy, use the Image Upscaler; to change the file type entirely, use the Image Converter. If the dimensions are already correct and only the file weight is too high, use the Image Compressor.