Rear gear change vs driveshaft RPM

Anyone have a good formula for calculating what wheelspeed should be after a rear gear change? I did a search and seen that Canter posted some good numbers for different rear gear combos, but it would be nice to have a formula to plug numbers in and get a 'close' guesstimate. Currently running 3.89s for quarter mile stuff but thinking of changing to something in the 4.56 to 4.71 range for correct rpm at the stripe and less rpm drop between shifts for 1/8 mile stuff.