The formula
cost of an ingredient = amount used ÷ pack size × pack price
Where it comes from
Confusing the price of the pack with the cost of the ingredient is what makes a home-cooked dish look ruinous. Three hundred grams of rice out of a one-kilo bag that cost two is sixty cents, not two: the rest of the bag is still in the cupboard. The right sum is the proportion, and the answer usually surprises people on the low side. The full shop is shown separately because that is what goes through the till, even if you do not use it today.
How to work it out by hand
- Note for each ingredient how much you use and how much the pack holds
- Divide what you use by what it holds and multiply by the price
- Add up all the ingredients
- Add the energy and divide by the servings
What is worth knowing
Energy is easy to estimate: a hob uses around 1.5 kWh per hour and an oven about 2, so half an hour of oven is one kilowatt hour, which at your tariff usually lands between fifteen and thirty cents. It is worth counting on long roasts, where it can beat some of the ingredients. Comparing this figure with the same dish in a restaurant or ready-made is the commonest use of this calculator, and for that the number that matters is the cost per serving, not the total.