Calculate savings from buying generic over branded food.
Pack sizes rarely match between a branded product and its store-brand equivalent, and that is not accidental — a slightly smaller store pack at a much lower headline price can obscure the true comparison in either direction. Reducing both to cost per 100 grams or millilitres removes the trick. The annual figure then holds quantity constant, using the branded pack size as the reference, so the saving reflects buying the same amount of food rather than the same number of packs. Applied across a whole basket, a 30 to 40 percent unit saving on staples is where most of the value of switching sits.
Unit cost
Per 100 units = pack price / pack size x 100
Saving
Saving % = (branded unit cost - store brand unit cost) / branded unit cost x 100
Because pack sizes differ, often deliberately. A store brand at 20 percent less money but 25 percent less product is more expensive, not cheaper. Cost per 100 grams or millilitres is the only comparison that survives a size difference.
Often they come from the same factories under contract, particularly for staples like flour, sugar, milk and tinned tomatoes, where there is little to differentiate. The gap tends to be wider for products where recipe and formulation matter — chocolate, coffee, cleaning products.