On the shipping tab, create 3 rules:
1) Less than 1kg:
Triggers:
SubTotal For Any Column
If the subtotal of column [TotalWeight] is [<] a value of [1]
calculations:
Flat rate of 5
2) Greater than 1kg Less Than 3kg:
Triggers:
SubTotal For Any Column
If the subtotal of column [TotalWeight] is [>=] a value of [1]
AND
SubTotal For Any Column
If the subtotal of column [TotalWeight] is [<=] a value of [3]
calculations:
Flat rate of 7.5
3) Greater than 3kg:
Triggers:
SubTotal For Any Column
If the subtotal of column [TotalWeight] is [>] a value of [3]
calculations:
Flat rate of 8.5
