You will need 4 buttons - approximately 5/8” (1.5 cm). Rowan used buttons with two holes.

Finished measurements:
Chest circumference: 19.75(20.5, 21.25, 22)“ 50(52, 54, 56) cm
Finished length:9(9.75, 10.5, 11.5)” 23(25, 27, 29) cm
Sleeve to armhole: 4.25(5, 5.75, 6.5)“ 10.5(12.5, 14.5, 16.5) cm

Yarn used:
Rowan Cotton Wool
Shown in 203 Tiny and 208 Pickles - 2(2, 3, 3) balls