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Area of octagon    2 s^2 (1+sqr2)

3 :     2 (9)*(1+sqrt2) = 43.456 in²      perimeter  =24 in     per/area = .55228

6 in    2(36)(1+sqrt2)= 173.823 in^{2     perimeter} =48             per/area =.27614

or marbe you want   ratio    per1/per2          area 1 / area2      I'll let you calc those     (perimeter doubles  area quadruples)