If you have gears, you need to know the gear ratio between your motor and your axle. Also need to know your wheel diameter. Then you can use this equation:
Speed=RPM*GR*(2*pi*R)
Where:
RPM is your motor rotations/minute
GR is your gear ratio
pi = 2.14
R is your wheel diameter
It would have been nice if you would have explained your initial post rather than simply edit it. Leaving those of us who initially replied hanging in mid air.