Pendulum Wave calculations for length of string

[OdyStarr]

can I plug in a formula to calculate the length of string for a 9, 12, 14, 16 pendulum wave?

[#2]

If your pendulum period is in cell A1 then the length can be calculated as:
=A1^2*9.8/(4*Pi()^2)

[#3]

Thanks, thought I might have to use some kind of matlab.