Filewhisk

Guides to file size, formats and quality

Short, practical write-ups about the things our tools do: what actually makes a file smaller, which format to pick, where a PDF's megabytes really are.

Every guide is built on measurements we ran ourselves rather than numbers copied from other articles. Where a figure appears, the test file, the settings and the encoder are named, so you can repeat the test and get the same result.

Social media image sizes, checked against each platform's help page We read every platform's own help page. Four of the sizes most guides repeat are no longer what the platforms say, including YouTube's thumbnail. 4 min read Upload size limits for email, chat and photo applications Every number in the table comes from the service's own help page, and one of them is smaller in practice than it looks: a 25 MB email limit fits an 18 MB file. 5 min read One photo, eleven countries Only 23 of the 55 country pairs we checked have any overlap at all, and resizing a US photo fails Schengen, Japan, Australia and India outright. 7 min read What actually makes a GIF large The advice is always the same five levers in the same order. We measured them, and the winner changes completely depending on what is in the GIF. 6 min read When 500 KB is not 500 KB The same file is two different sizes depending on who is counting, and the gap is exactly wide enough to get your upload rejected. 6 min read What actually removes the location from a photo Measured results for eight image operations, and the one case where a "compressed" photo still carries your GPS coordinates. 6 min read What is actually inside a PDF after you sign it We took a signed PDF apart object by object. The signature is an image drawn onto the page, and that has consequences worth knowing. 6 min read JPEG, PNG, WebP or AVIF: which one to actually use Measured sizes for the same photo in four formats, and the cases where the smallest file is the wrong answer. 4 min read How to make a photo smaller without ruining it The same 15-megapixel photo, compressed 40 different ways, with every file size measured - and the one setting that does most of the work. 5 min read Where a PDF's file size actually comes from Two PDFs taken apart object by object, then compressed - and why the same tool shrinks one by 96% and the other by 13%. 4 min read

Why we measure instead of repeating

File-size advice online is mostly inherited: one article says lowering quality is the main lever, the next twenty repeat it, and nobody re-checks. When we measured it, resizing a photo turned out to save four times more than the quality slider everyone recommends, and re-saving a JPEG ten times at the same settings turned out to do almost no damage at all — the opposite of the advice you will find nearly everywhere.

The guides are written to be useful without the tools on this site. Where one of our tools is the convenient way to do the thing being described, it is linked — but the explanation works the same in Photoshop, in Preview, or on a command line.

Missing something? If a guide would have saved you time, tell us at hello@filewhisk.com — the requests that explain the task you were trying to finish are the ones that get written first.