My lighting layout is pvc fence.post spacing 6'apart total #of post 11 total wire lenght 170'installed 12gauge what size 12v transform will i need?

Hi Bob, the transformer size depends on the total wattage consumed by your lights. If for example you have 11 lights of 10 watts each, you will need 11 lights x 10W = 110W minimum wattage rating on your transformer. The fact that you have 170' of wire is fine since you used some 12 gauge wire.