Materials: 24" x 24" paver
(4 SF ea), 1000 SF patio = 250 pavers (for the field, 1 pedestal each paver)
Perimeter: (LF) 20'x50' = 20'+50'+20'+50' = 140 LF multiply by 12"
= 1680" divided by 24" (dimension of paver)  = 70 pedestals
Total: 250 + 70 = 320 pedestals needed

Materials: 18"x18" paver
(2.25 SF ea), 800 SF patio = 320 pavers (for the field, 1 pedestal each paver)
Perimeter: (LF) 20'x 40' = 20'+40'+20'+40' = 120 LF multiply by 12"
= 1440" divided by 18" (dimension of paver) = 80 pedestals
Total: 320 + 80 = 400 pedestals needed