You will need six buttons. Rowan used # BV1800 from Bedecked.

Finished measurements:
Body circumference: 35.5(40, 43.5, 47.5, 51)“ 90(101, 110, 121, 1310 cm
Finished length: 17(17.5, 18.5, 19.5, 20)” 43(45, 47, 49, 51) cm
Sleeve length to underarm: 17.5(17.5, 18, 18, 18)“ 45(45, 46, 46, 46) cm

Yarn used:
Rowan Alpaca Classic
109 Deep Teal - 6( 6, 7, 8, 8) balls