Go to Catalog -> Attributes-> New Attribute.
Call it Weight. Public name Weight (or Weight in kg, KG or what you want) Type of Attribute: List
Save.
Add New Value into the Group of Attribute Weight you just made. Call the Value 1kg save and Add New Value. 2kg, 3kg, 4kg, 5kg, 6kg...... and 10kg.
Save all of them even if you don´t use all of them if all your products.
Go to your Catalog-> Products -> Sugar (you mentioned). In the first tab Basic adjustments, at the right, Combinations, select Product with Combinations.
Then go to Combinations. Select the combinations you use for this product, go to Weight and select for example (if you only sell sugar in 1kg, 2kg, 5kg and 10kg) those values. In other products you can select only 5kg and 10 kg
Generate. After this you have the combinations.
Say we want to sell the sugar at 1€ one kg, 1,95€ for 2kg, 4,50€ for 5kg, 8€ for 10 kg
Select the cheapest value (1kg) edit with the pencil icon, set the price for 1kg, for example 1 euro, if it is final price Tax included. Tax excluded if you want to add taxes after. (If you at the beginin set the product price at 1€ you don´t have to edit 1kg, set to 0) If you didn´t set any original price, then set it to 1€
Edit 2kg set impact on price 0,95 (plus the original price for 1kg we get the final price set to 1,95€)
Edit 5kg, set Impact on price 3,50. Then you will get the final price of 4,50€
Edit 10kg, set Impact on price 7. Then you will get the final price of 8€