Webtoon format guide
Webtoon format specifications: what to check before you upload
WEBTOON Canvas is not one canvas size. It sets separate limits for the series thumbnail, the episode thumbnail and the episode images — and the episode images have the smallest per-image limit of the three. Getting the first two right and the third wrong is the most common upload failure.
What are the WEBTOON Canvas image size requirements?
A square series thumbnail must be 1080 × 1080 px under 500 KB. A vertical series thumbnail must be 1080 × 1920 px under 700 KB. An episode thumbnail must be 160 × 151 px under 500 KB. Each episode image must stay under 800 px wide and under 1280 px long, at under 2 MB.
| Asset | Dimensions | Maximum file size | Accepted formats | Filename rule |
|---|---|---|---|---|
| Series thumbnail — square | 1080 × 1080 px | under 500 KB | JPG, JPEG, PNG | English letters and numbers only |
| Series thumbnail — vertical | 1080 × 1920 px | under 700 KB | JPG, JPEG, PNG | English letters and numbers only |
| Episode thumbnail | 160 × 151 px | under 500 KB | JPG, JPEG, PNG | English letters and numbers only |
| Episode image (each) | under 800 px wide and under 1280 px long | under 2 MB after slicing or resizing | JPG, JPEG, PNG | — |
| Upload batch | up to 100 images | up to 20 MB in total | — | — |
Source: WEBTOON's official Before You Publish Checklist. Confirm these numbers against WEBTOON's current published checklist before you upload — platform limits change, and the destination's own page always wins over any guide, including this one.
How do I format a webtoon for mobile reading?
Confirm the destination's current limits, scale width and height together, keep faces and dialogue clear of the cut lines, check the file size of every segment after slicing, and preview the lettering on an actual phone before uploading.
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01
Confirm the destination's current limits
Width, height, file size, format, filename and episode limits differ by platform and change over time. Read them on the destination's own creator help or publishing checklist.
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02
Preserve the aspect ratio
Scale width and height together. Stretching one dimension independently distorts lettering first, before it distorts the art, and lettering distortion is the harder problem to spot.
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03
Split a long image at safe lines
Keep faces, dialogue and important action clear of the cut. A split through a speech bubble reads as an error even when nothing is technically wrong.
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04
Check the per-image size after slicing
Slicing one tall image produces several files, and the file size limit applies to each of them. A file that passed as one piece can fail as seven.
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05
Preview for legibility on a phone
Lettering that reads comfortably on a desktop monitor is often too small in the app. Preview on the device readers will actually use.
Why 1080 × 1920 is the wrong size for an episode image
Series thumbnails are 1080 × 1920, which is the size most creators learn first. Episode images are not. A single episode image must stay under 800 px wide and under 1280 px long, with a 2 MB cap. WEBTOON's system automatically slices and reduces images that exceed the maximum dimensions, so an oversized upload is not rejected — it is silently changed.
That distinction matters because the two failures look completely different. A rejected upload tells you something is wrong. A silently optimized upload does not: the episode publishes, the reader sees something, and the artwork on the screen is not the artwork you approved. If you want the pages to survive untouched, upload within 800 × 1280 px and stay inside the total file size limit.
Two smaller rules sit alongside the dimensions. Thumbnail filenames may only use English letters and numbers, so a title with spaces, accents or punctuation needs a working filename before it needs a working image. And WEBTOON advises against putting text on a series thumbnail at all — it distracts from the art and is frequently hard to read at the size the thumbnail is actually displayed.
The three sizes people confuse
Almost every webtoon sizing question is really a question about which asset is being sized. Three different things carry three different limits, and only one of them is the artwork.
- The series thumbnail is the cover readers see in the app. It comes in a square version and a vertical version, and it is the largest thing you upload.
- The episode thumbnail is the small image beside an episode in the list. It is tiny — a few hundred pixels wide — and it is usually the asset creators forget to prepare until the upload form asks for it.
- The episode images are the actual pages. They carry the smallest per-image limit of the three, which is the opposite of what most creators assume.
A creator who designs at 1080 × 1920 because the thumbnail uses that size will hand in episode images that the platform then slices and reduces. Nothing errors. The artwork just comes out different from what was uploaded, and the difference is only visible if someone compares the upload against the published page.
How to verify a limit instead of trusting a guide
Platform limits are published, change without much notice, and are sometimes different between the web uploader and the app. Treat any sizing guide — including this one — as a starting point, then confirm against the destination.
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01
Open the destination's own documentation
Use the platform's current creator help or publishing checklist, not a blog post about it. Third-party summaries go stale silently.
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02
Find the number for the exact asset you are preparing
Thumbnail, episode thumbnail and episode image carry three different limits. Reading the wrong row is the most common mistake.
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03
Note the file size cap, not just the pixel cap
The file size is usually the limit people hit first, especially after slicing a long strip into segments.
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04
Check whether the platform auto-processes oversized uploads
If it does, an oversized file is not a rejection — it is a silent edit. That changes what you need to verify after uploading.
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05
Export, then re-check the file you actually produced
Inspect the output file, not the settings you typed. Export dialogs and post-processing steps can change dimensions on their own.
Working with a long vertical image
A vertical webtoon is drawn as one long strip, but it is rarely uploaded as one file. Destinations cap image height, so the strip gets split into ordered segments. Two things decide whether the split is clean: where the cut lands, and whether the segments stay in order.
Keep faces, dialogue and important action away from the cut line. And number the segments so they cannot reorder in transit — a folder sorted as plain text will place 10 before 2 unless the numbering is zero-padded to the same width.
The StoriesToon webtoon size calculator scales by aspect ratio and estimates how many segments a long image becomes. The image splitter sets target limits, shows the cut lines, and exports numbered segments in order.
Choosing a width for a vertical webtoon
Vertical webtoons are read on phones, held one-handed, at arm's length. That has two consequences worth designing for. First, the effective canvas is narrow — a composition that needs a wide frame fights the format. Second, lettering has a floor: text that is comfortable on a desktop monitor is often too small in the app, which is why previewing on an actual phone before uploading is worth the extra minute.
Both consequences push in the same direction: fewer panels per screen, larger lettering, and more deliberate use of vertical space. A page designed for print will read as dense in the app, and density is the thing mobile reading punishes hardest.
Format questions
What are the WEBTOON Canvas image size requirements?
A square series thumbnail must be 1080 × 1080 px under 500 KB, a vertical series thumbnail 1080 × 1920 px under 700 KB, an episode thumbnail 160 × 151 px under 500 KB, and each episode image under 800 px wide and under 1280 px long at under 2 MB. Only JPG, JPEG and PNG are accepted.
How do I format a webtoon for mobile reading?
Confirm the destination's current limits, scale width and height together, keep faces and dialogue clear of the cut lines, check the file size of every segment after slicing, and preview the lettering on an actual phone before uploading.
Are webtoon specifications the same on every platform?
No. Width, height, file size, format, filename and episode limits differ by platform and change over time. Confirm the current destination requirements before exporting.
Should I preserve the original aspect ratio?
Yes. Scale width and height together so the original aspect ratio is preserved. Stretching one dimension independently distorts lettering first, before it distorts the art.
How can I split a long webtoon image?
Use the StoriesToon webtoon image splitter to set target limits, review the cut lines, and export numbered segments in order. The size calculator scales by aspect ratio and estimates how many segments a long image becomes.
Why are the thumbnail and the episode image different sizes?
They are different assets with different jobs. The series thumbnail is a promotion image at 1080 × 1080 or 1080 × 1920; an episode image is capped at 800 × 1280. Learning one size does not give you the other.
What happens if my image is too large?
WEBTOON's system automatically slices and reduces images that exceed the maximum dimensions. The upload is not rejected — it is silently changed. To keep the artwork untouched, upload within 800 × 1280 px and stay inside the total file size limit.
How many images can I upload at once?
WEBTOON's published checklist allows up to 100 images and up to 20 MB in total per upload, with a 2 MB cap applying to each sliced, resized or unchanged image.