Here is a guide to how much sugarpaste we use @ Bakeworld to cover.
6” round (15.24 cm) 5” square (12.7 cm) 500g
7” round (17.78 cm ) 6” square (15.24 cm) 600g
8” round (20.32 cm) 7” square (17.78 cm) 800g
9” round (22.86 cm) 8” square (20.32cm) 1kg
10” round (25.4 cm) 9” square (22.86 cm) 1kg 250g
11” round (27.94 cm) 10” square (25.4 cm) 1kg 500g
12” round (30.48 cm) 11” square (27.94 cm) 1kg 750g
13” round (33.02 cm) 12” square (30.48 cm) 2kg