Gea ratio comparison site?

[Rolls]

As title - can anyone direct me in the direction of a site that maybe able to offer comparisons, or tell me how to work out the spread of gears that i have currently...

(Looking to go from 3x9 to 2x10, and want to have (broadly) the same upper and lower levels if possible...)

Cheers!

[walm]

You could just count the teeth (assuming your crank length doesn't change).
Then use the magic of ratios.

Otherwise AASHTA: http://sheldonbrown.com/gears/