You will need 5(5, 6, 6, 6) buttons.

Finished measurements:
Chest circumference - 26.75( 29, 30.5, 33.25, 35.5)“ 68( 73.5, 77.5, 84.5, 90) cm
Finished length: 15.75( 17.25, 19, 20.5, 21.75)” 40( 44, 48, 52, 55) cm
Sleeve seam: 6(7.5, 9, 10, 10.75, 12.5)“ 15( 19, 23, 27, 32) cm

Yarn used:
Rowan Summerlite DK
Shade 479 Giggle - 5(5, 6, 6, 7) balls