I have to express the following logic.

Available Plate Thickness 8, 10, 12, 14, 16, 18, 20, 25, 28, 30, 32

The logic is if my calculated thickness is, THKcal < 8, Thk Provided,
THKprov = 8

8< THKcal <10
THKprov = 10

10< THKcal <12
THKprov = 12


........................... ................


......................... ....................

28< THKcal <30
THKprov = 30

30< THKcal
THKprov = 32

Now this logic I have tried as
=if(THKcal<8,8,if(and(8<THKcal,THKcal<10),10,if(an d(10<THKcal,THKcal<12),12,........................ if(and(28<THKcal,THKcal<30),30,32))...)
But problem is I can no go beyond certain amount of limit for the nested loop.
What is the solution. Any easier way to express it. Anyway thanks.

Regards