Resize Image for Mastodon — Free Tool
Drop in one picture and get every Mastodon size back, cropped to fit. All 5 Mastodon formats are ticked before you start, including Post Image 1920x1080, Post Image (Square) 1080x1080 and Header 1500x500, so upload and download is the whole workflow. Cover-fit cropping, a top, centre or bottom focal point, JPEG or PNG, and nothing is ever uploaded.
Features
- Every Mastodon image size in one pass: Profile Photo 400x400, Header 1500x500, Post Image 1920x1080, Post Image (Square) 1080x1080, Post Image (Portrait) 1080x1350
- Mastodon formats arrive pre-selected, so a single upload produces Post Image 1920x1080, Post Image (Square) 1080x1080 and Header 1500x500 without touching a control
- Cover-fit cropping: the picture is scaled to fill each box and the overflow is trimmed, never stretched
- Per-size focal point of top, centre or bottom, so a face near the top of the frame survives the tall crops
- The other 10 networks are still listed underneath, 77 sizes across 11 platforms, and everything runs in your browser
Frequently asked questions
Which Mastodon sizes does this produce?
All 5 of them: Profile Photo 400x400, Header 1500x500, Post Image 1920x1080, Post Image (Square) 1080x1080, Post Image (Portrait) 1080x1350. Each one is exported at those exact pixel dimensions, so nothing is left for the platform to resample.
What happens to an image that is the wrong aspect ratio?
It is cover-fit cropped. The picture is scaled up until it fills the target box completely, and whatever hangs over the edge is cut away, so the shape is never squashed or stretched. What survives the cut is your choice: the focal point control on each size crops from the top, the centre or the bottom. Centre is the default and suits most photographs, top keeps heads and headlines in a tall crop, and bottom is there when the subject sits low in the frame.
Should I export as JPEG or PNG?
JPEG at quality 0.92 is the default and is right for photographs, giving far smaller files at effectively the same visible quality. Pick PNG for graphics, screenshots, logos and anything with flat colour, hard edges or text, where JPEG compression leaves visible artefacts.
Why does a big photo still look sharp at 1920x1080?
Because the reduction happens in halving steps. One huge downscale in a browser canvas throws away most of the source rows outright and looks aliased, so the image is halved repeatedly until it is within twice the target size, then drawn once at the exact dimensions, with high quality smoothing on at every step.
Are my images uploaded anywhere?
No. The whole tool runs on a canvas inside your browser. The file never leaves your device, there is no server round trip, nothing is stored or logged, and no account is needed.
Schedule Mastodon posts
Done writing? Schedule and bulk publish it to Mastodon with BulkPublish.
