Your giant image won't save as WebP — the 16383-pixel ceiling

2026-11-13

Most images are nowhere near any format's size limit. Then you try to turn a very long stitched screenshot or a full-page capture of a website into WebP, and it simply won't work. The cause is a hard ceiling built into the format itself, and once you know the number, the fix is arithmetic.

The documented limit

Google's WebP FAQ (developers.google.com/speed/webp/faq, checked 2026-10-08) states that the maximum pixel dimensions of a WebP image are 16383 × 16383. The reason given is that WebP is bitstream-compatible with VP8, which uses 14 bits to store the width and the height.

Notice that this is a limit per side, not on the total number of pixels. An image of 1000 × 20000 pixels is modest in total, but its height is over the ceiling, so it can't be a WebP at that size.

Which images hit it

• Stitched screenshot strips. Ten phone screenshots of 2400 pixels each, stacked, make a strip 24,000 pixels tall.
• Full-page captures of long web pages, which are often tens of thousands of pixels tall.
• Panoramas produced by stitching software.
• Long infographics and timelines designed as one tall canvas.

JPG and PNG allow much larger dimensions, which is why these images exist and work in the first place — the problem only appears when you ask for WebP.

What our converter does — and doesn't promise

Our PNG to WebP converter draws your image onto a canvas in your browser and asks the browser's own WebP encoder for the file. Nothing is uploaded. What a browser does when asked to encode past the format's ceiling isn't something we control, so we don't promise any particular outcome there. What we do guarantee: the file you download is named by the format that was actually produced. If a result doesn't end in .webp, it isn't a WebP, and we won't pretend otherwise. The dependable approach is to bring the image under 16383 pixels on its long side before converting.

Option one: scale it down

Work out the scale from the long side: 16383 divided by the current long side. For a 24,000-pixel-tall strip that's about 0.68.

• In Resize image, choose Percentage and set 68%: 1080 × 24000 becomes about 734 × 16320 — just under the ceiling.
• Or choose Pixels, keep the aspect ratio locked, and type the width; the height follows.

Be honest with yourself about the result: shrinking a tall strip this way also narrows it, and text in screenshots gets smaller with it. If the strip is meant to be read, splitting may serve you better.

Option two: split it

Cut the image into parts that are each under the ceiling, at full width. In Crop image, keep the ratio on Free and type the numbers: for a 1080 × 24000 strip, width 1080, height 12000, Y position 0 for the first half. Apply and save, then use Adjust area, set Y to 12000, Apply and save the second half. Each part converts to WebP without trouble, and nothing gets smaller.

Option three: keep the format you have

WebP's advantage is smaller files on web pages. For a document-like strip that will be downloaded or shared rather than shown inline, a PNG or JPG at full size is a perfectly good answer — and our stitch tool produces a JPG anyway.

The short version

• WebP's maximum is 16383 × 16383 pixels, a per-side limit (Google WebP FAQ, checked 2026-10-08).
• Tall stitched strips, full-page captures and panoramas are the usual offenders.
• Scale by 16383 ÷ long side, or crop the image into parts under the ceiling.
• Our converter names files by the format actually produced — check for .webp.