Model kits come in many different scales or sizes. All those numbers can be confusing, but it is actually fairly easy to understand how scale works. The "scale" of a model is it's size relative to the size of the "real" version. So compared to a 1:24 scale model, the real version is 24 times larger in size or 1:1 in scale.
Example; In the pictures below...
- The model on top is "1:18 Scale", which means it is one eighteenth the size of the real thing.
- The next is "1:24 Scale", so it is one twenty-fourth the real thing and smaller than "1:18 Scale".
- And the last is "1:43 Scale", so it is one forty-third the real thing and smallest of the three.
For a list of all model scales, check out TheWikipedia list of scale model sizes.