You will also need a circular needle size US 3 (3.75 mm), at least 16” (40cm) long

You will need one button. Rowan found one at Groves & Banks in the UK.

Finished measurements:
Back: 14(15, 16, 16.5, 18.5)“ 35(38.5 ,40.5, 42.5,47.5) cm
Length: 15(17, 18.5,20, 21.5)” 38(43, 47, 51, 55) cm
Sleeve length: 10(12, 13.5, 15, 17)“ 26(30, 34, 38, 43) cm
Raglan cap: 6(6.5, 6.5, 7, 8)” 15(16, 17, 18, 20) cm

Yarn used:
Rowan Softyak DK
Plain 232 - 6(7, 8, 10, 11) balls