Yarn requirements given in 50 gram balls.
To fit chest/bust:
24/26 ins (61/66 cms) 9 balls and 5 buttons
28/30 ins (71/76 cms) 12 balls and 5 buttons
32/34 ins (81/86 cms) 15 balls and 5 buttons
36/38 ins (91/96 cms) 16 balls and 6 buttons
40/42 ins (102/107 cms) 18 balls and 6 buttons
44/46 ins (112/117 cms) 21 balls and 6 buttons.

Leaflet also gives instructions for a round necked cardigan

http://www.ravelry.com/patterns/sources/sirdar-squiggle-s...