A GIF stores its animation frame by frame using an old, lightweight compression scheme that wasn't designed for photographic motion. It can't use the clever inter-frame compression that modern video codecs (like H.264 in MP4) rely on, where only the changes between frames are stored.
That's why a clip that's a few hundred kilobytes as MP4 can be several megabytes as GIF. To keep GIFs small, reduce the frame rate, dimensions and colour palette — or convert to MP4 when a real video will do.
Try Compress GIF or Resize GIF to bring the size down.
No compression across frames
This is the main reason. Video codecs store a frame as the difference from the previous one, so a clip where a small part of the picture moves against a still background costs almost nothing to continue. GIF stores each frame nearly independently, compressed only within itself, using a scheme designed in 1987. A ten-second GIF is closer to a hundred separate images than to a video.
Dithering noise
The 256-colour limit forces dithering on any content with gradients, and dithering scatters pixels in fine patterns specifically so the eye blends them. That destroys the local uniformity GIF's compression depends on, so the file grows precisely where the picture needed the most help. It is a genuine trap: the setting that makes a GIF look acceptable is also the one that makes it heavy.
The three levers, in the order to pull them
Trim first. Every frame removed is data that no longer needs storing, and length dominates GIF size — cutting ten seconds to three removes roughly seventy per cent before anything else happens. Crop next, to lose parts of the frame that were never the point. Then resize, which reduces pixels quadratically: halving both dimensions removes about three quarters of what remains. Only then lower the frame rate and compress. Reversing this order wastes most of the work.
What size to aim for
Under about 5 MB for messaging and email, and under 2 MB for anything going on a web page. Many platforms enforce their own limits and will reject or silently re-encode larger files. If a clip cannot get there without looking bad, that is a signal the content wants to be video rather than a GIF.
The honest answer
Sometimes the right fix is not to make the GIF smaller. If the destination accepts video, converting to MP4 typically cuts the size by 80-90% and looks better at the same time.