Why are Toric contact lenses bigger?

Hello!

I was just wondering:
Why are Toric contact lenses bigger? ~14.4, 14.5 DIA and normal sph
lenses ~ 14.0, 14.2 DIA

What is the appropriate equivalent of a 14.5 toric lense for a normal
sph lense?

(For example: I was measured half a cylinder astigmatism and no
dioptry in the right eye and since the lowest value of a toric lense
is -0.75 cyl i would like to try with a normal spheric soft contact
lense with -0.25 sph power.. because with a toric -0.75 i see blurry..
and would like to try the half of cyl rule for sph lense and don't
know wheather to get a 14.0 or 14.2 DIA? 14.5 toric was comfortable)

Thanks!

Have a nice day