Tumblr Media Checker
Drop in a photo, GIF or video and see whether it clears Tumblr’s limits: real file type, size, dimensions and length, checked in your browser.
How to use the Tumblr Media Checker
Drop in the file
Drag a photo, GIF or video onto the card, or click to pick one. The file is read on your own device and is never sent to a server.
Read what the file actually is
The checker reads the file header, not the filename, and reports the real type: format, file size, pixel dimensions and duration for video. That is how a photo named .jpg that is really something else gets caught.
Check each row against Tumblr’s rules
Every property is marked pass or fail: images against 20 MB and jpg, jpeg, png, gif or webp, video against 90 MB and 10 minutes with mp4 or mov.
Fix an image without leaving the page
If an image fails, convert it to JPEG, compress it under 20 MB or resize it here, then download the result and post it.
Re-export video from your editor
Video is measured and explained, never converted and never uploaded. Use the report to re-export at a size and length that clears the limits.
Tumblr media limits this checker tests against
Images are held to 20 MB, in jpg, jpeg, png, gif or webp, which is what Tumblr documents. A GIF counts as an image here and shares that same ceiling, so a heavy loop is the single most common reason a gifmaker gets stopped before the post even goes up.
Video is held to 90 MB and 10 minutes, in mp4 or mov. Those are the two formats Tumblr documents for posting video, so anything else has to be re-exported before it will go up.
One post carries up to 30 images. Video does not mix with images in the same post: a native video goes up on its own. Getting the count right matters as much as the file itself, because a set that is too large fails as a whole.
Two ceilings, named honestly
The 90 MB video ceiling on this page is JuzPost’s own. It sits below the ceiling Tumblr documents for direct uploads, which means a file can be perfectly fine for Tumblr’s web uploader and still be too large to schedule through JuzPost. That is a deliberate margin, not a Tumblr refusal, and this checker says so rather than letting you guess.
Images are the opposite case. The 20 MB here is Tumblr’s own documented ceiling, not a margin of ours, so a file that clears this page clears what Tumblr asks for. Several guides still print 10 MB, which was the older figure. Knowing which ceiling you actually hit is the difference between a five second fix and an afternoon of re-exporting.
Why Tumblr says the format is not supported
The most common cause is a file whose extension does not match its contents. A photo saved from a phone or renamed by hand can end in .jpg while the bytes inside say something else entirely, and Tumblr checks the bytes. This tool reads the first bytes of the file and reports the true type, which usually ends the confusion in one line.
Colour profile is the other quiet culprit. An image exported for print rather than for screen can carry a profile Tumblr will not take, and the error you get back says nothing about colour at all. Re-saving as a standard screen JPEG, which the convert action here does, clears that class of failure.
Everything runs in the browser: no upload, no account, no queue, no copy of your file sitting on somebody else’s server. That also makes it fast, because there is no round trip to wait on when you swap files or try a fix.
Frequently asked questions
What is the maximum image file size for Tumblr?
20 MB per image, in jpg, jpeg, png, gif or webp. That is the figure on Tumblr’s own image troubleshooting page. Several guides still print 10 MB, which was the older ceiling, so a file those pages call too large may post without trouble.
What image formats does Tumblr accept?
jpg, jpeg, png, gif and webp. If your file is one of those and still gets rejected, the likely reason is that the extension does not match the actual contents. This tool reads the file header rather than the filename, so it tells you what the file really is.
What GIF size does Tumblr allow?
A GIF is treated as an image here, so it has to come in under the same 20 MB ceiling as any other image. Drop the GIF on this page and the file size row tells you immediately whether it clears that limit, along with its dimensions.
Why does my GIF only show one frame on Tumblr?
A frozen GIF is almost always a weight problem rather than a frame count problem. The heavier the loop, the more likely it is to be reprocessed or to fail to serve as an animation. Check the file here first: if it is close to the 20 MB ceiling, cut frames or reduce the width before you blame anything else. Old advice about frame counts and oversaturated colours has been copied around for years and no longer matches how Tumblr handles GIFs.
What is the maximum video size and length on Tumblr?
This page checks video against 90 MB and 10 minutes, in mp4 or mov. The 90 MB figure is JuzPost’s own ceiling, held below what Tumblr documents for direct uploads, so a larger file can still work when posted by hand. MP4 and MOV are the formats Tumblr documents, so prefer those.
How many photos can I put in one Tumblr post?
Up to 30 images in a single post. Video is separate: a native video post goes up on its own and does not mix with images in the same post. If a large set fails to publish, count the images before you start testing individual files.
Why does Tumblr say my file format is not supported?
Usually because the file is not what its name claims. An extension can be renamed, but the bytes inside cannot, and Tumblr reads the bytes. A print oriented colour profile causes the same unhelpful message. This checker reports the true type from the file header, and the convert action re-saves the image as a plain screen JPEG.
Does this checker upload my file anywhere?
No. The file is read and any image fix is applied entirely in your browser. There is no upload, no server copy and no account needed. Video is measured and reported only: it is never converted and never sent anywhere.
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