Compare milk, cheese and yogurt cost per serving.
Dairy products cannot be compared on price per kilogram, because their serving sizes differ by more than an order of magnitude. A 250 ml glass of milk and a 30 g slice of cheese are both one serving, so cheese at four times the price per kilogram can still be cheaper per serving. This calculator fixes a conventional serving for each product, converts the pack into servings, and reports cost on that basis — plus how many packs a month your household consumption actually needs, which is the figure that determines whether a larger pack's lower unit price is real or just an invitation to waste.
Servings per pack
Servings = pack size / serving size
Cost per serving
Cost = pack price / servings per pack
Because you do not eat a kilogram of each. Cheese costs far more per kilogram than milk but a serving is 30 grams against 250 millilitres, so the per-serving order can reverse entirely. Per-serving cost is the only basis on which a shopping decision makes sense.
Only if you finish it. Dairy has a short life once opened, so a larger pack's lower unit price is wiped out by anything you throw away. The packs-per-month figure tells you whether your household turns over a pack fast enough to justify sizing up.