You will need two buttons approximately 1/2” (1.3 cm).

Finished measurements:
Chest circumference: 20.5(21.25, 22.75, 23.25)“ 52(54, 57.5, 59) cm
Finished length: 9.75(10.5, 11.5, 12.25)” 25(27, 29, 31) cm
Sleeve length to armhole: 5(6, 6.75, 7.5)“ 13(15, 17, 19) cm

Yarn used:
Rowan Summerlite DK
Shade 454 Mushroom - 3(3, 3, 4) balls