You will need four buttons.

Finished Measurements:
Back width: 20(21.5, 22.5 ,24, 25, 26, 27)“ 51(54.5, 57 ,60.5, 63, 65.5, 69) cm
Finished length: 28.5(29, 30, 30, 30.5, 30.5, 31.5)” 72(74, 76, 76, 78, 78, 80) cm
Sleeve to underarm: 18(18.5, 19, 19.5, 20, 20.5)“ 46(47, 48, 49, 50, 51, 52) cm

Yarn Used:
Rowan Alpaca Soft DK
Shade 204 Classic Brown - 12(13, 14, 15, 16, 17) balls