This, a 1/18 scale diecast car is usually about 24 - 30cm (depending on the size of the actual car). A 1/24 scale diecast car is generally about 16 - 20cm. Many of the cars made in the smaller scales (1/32-1/38) are actually made so that the car will be exactly 5 inches long, regardless of the scale.

Finally, it's important to note that larger vehicles, such as trucks or construction vehicles, are often made on a smaller scale (1/50 or 1/64), but are in fact about the size of 1/24 scale cars, since the actual vehicle is much larger.