Too much Youtube I guess.

NOWAY.. The calculation will get back to old concept:

The material for spherical area is a cylinder with l = C = 6.34314 and h or w = 1/2C = 3.17157.

And then the height and length gets curved and lost 0.2071 part each.

sA = C × 1/2 C × 0.79289 × r² = 6.34314 × 3.17157 × 0.79289² = 12.6475 r².

That's it.