How to make a GIF
Drop in an MP4, MOV or WebM. The first 15 seconds are selected, the most a GIF can hold here; drag the handles on the strip of frames to the moment you want. Pick a width and a frame rate, then press Make a GIF. The line above the button gives the size, the number of frames and roughly how big the file will be.
Keeping it small
A GIF stores every frame as a whole picture in at most 256 colours, so it grows fast. Each step down in width cuts it a lot: 320 wide has under half the pixels of 480. 10 frames a second instead of 20 halves it again. Three seconds at 10 frames a second is just 30 frames.
Crop and speed
Crop the clip to 1:1 or 9:16 first and the GIF takes that shape; it is never wider than the crop. Speed works too: at 2×, up to 30 seconds of the video fit into a 15-second GIF. GIFs never have sound.
Questions
Why 15 seconds at most?
A GIF has none of the compression a video has, so long ones get very large: 15 seconds at 20 frames a second is already 300 full pictures. For anything longer, save it as an MP4 instead, which is far smaller.
Can I turn a GIF into a video?
Yes: the GIF to MP4 converter does it in one step, and the file usually comes out much smaller than the GIF.
How is this different from the MP4 to GIF converter?
The MP4 to GIF converter turns the whole file into a GIF in one step, at its own size and frame rate, which suits a clip that is already short and small. This page lets you pick the moment, crop it, and set the width and frame rate, so the GIF stays a size you can send.