How would you go about figuring out the gear ratio?

Question

I mean, yes, if it were a circle, all i'd have to do is find the circumfrence of the back gear, (on a bike) and divide the bigger front gear's circumfrence by that. but the thing is, the number of teeth vary from one set to another, and i want to make sure i'm putting my money in a new set of gears with a good enough difference. Also, some gear sets have slightly elliptical gears to make pedaling easier, (mine are too, but very very slightly.)

i'll need to know how to figure in the number of teeth and the tooth size if possible. thanks!

Answer 1

Count the teeth.
The tooth size is determined by the chain pitch, and must be the same for all sprockets in the set, both front and rear.
If the circumference is available, it's the number to use,
as a slightly eliptical shape won't effect the over-all ratio and the pitch is fixed by the chain.

Answer 2

gear ratios are all figured out with by dividing the driven gear by the driving gear so basically you would divide the amount of gear teeth on the rear gear by the amount of teeth on the pedaled gear and thats your gear ratio it works anytime there is a gear set