I have a model motorcycle that is all metal parts and is 18" long. Since the size all the models online are given in a scale, What scale to an actual motorcycle do I have and where do I look to find a value?

See below.

Step-by-step explanation:

The model may have the scale written somewhere. Try looking for it.

If you can't find it, then you can calculate this way.

Search online for the real motorcycle's length.

Then divide the scale model's length, 18 inches, by the real length. Express that as a ratio. That is the scale.

Let's say the length of a real motorcycle of this type is 90 inches.

Divide 18 inches by 90 inches.

18/90 = 1/5

The scale, then, is 1:5.