It depends on how big or small the stones are. There are no agreed boundaries separating pebbles from stones, and stones from boulders.
Two main types; precious stones and non precious stones.
13st = 82.55kg
9 stones is 57.2kg
19 stone = 120.656kg (6.35029 kg per stone).
10.85 stone.
54
7 inches
Assuming you don't want to cut and paste, then 4 x 11 = 44
This needs more information to supply a "best" answer. however.. assuming you mean 144 sq feet of patio and your stones are 16 inches x 20 inches. then accuratly you will need 66 stones. add at least 10% for cutting waste then i'd go buy 80 maybe 85.
7.1 Stones
11.32 stones
8.50354 stones.
13.7 stones
13.53 stones.
107.5kg = 16.928 stones
11.8104783 stones
stones has one syllable.