You will need 3 buttons. Rowan used .75” (20 mm) buttons from Textile Garden in UK (#TBG4915 - imitation horn)

Finished measurements:
Chest circumference: 36.75( 40.25, 44.75, 488.25, 52.5, 56, 60.5, 64, 69)“ 93.5( 102.5, 113.5, 122.5, 133.5, 142.5, 153.5, 162.5, 175.5) cm
Finished length: 17.75( 18.5, 19.25, 20, 20.75, 21.75, 22, 22.75, 23.25)” 45( 47, 49, 51, 53, 55, 56, 58, 59) cm

Yarn used:
Rowan Summerlite DK
A. 477 Cecily - 4(4, 5, 5, 6, 6 ,7, 7, 8) balls
B. 475 Pickles - 2(2, 2, 2, 3, 3, 3, 34) balls