Learn to interpret your results
Price per usable kilo: when a larger pack stops saving money
Published on
A bigger pack saves money only when enough of its contents are used. A shelf price compares what you buy, while your household budget also pays for what remains unused. Separating those two quantities makes a bulk-buying decision more useful.
Put the packs on the same scale
Suppose pack A costs £3 for 750 g and pack B costs £4 for 1.2 kg. These are invented prices for equivalent products, not a market survey. A costs £4 per kg; B costs about £3.33 per kg. Buying B still requires an extra pound at checkout. Lowest unit cost and lowest immediate outlay are different measures.
Count usable quantity separately
If all of A is used but only 80% of B is used, B provides 0.96 kg. Its cost per usable kilo is 4 / 0.96, or £4.17 after rounding. A now costs less for the quantity actually used. The assumed 20% loss is a scenario, not an estimate of normal household waste.
Divide the purchase price by purchased weight multiplied by the usable fraction. Dividing price by a percentage alone does not give a price per kilo. Keep the shelf comparison alongside the adjusted comparison so that the reason for the change remains visible.
Find the switching point
B matches A’s £4 per usable kg when one kilo of its 1.2 kg is used. That means using approximately 83.33% of the pack: losing one sixth gives a tie. Lower utilisation makes B more expensive in this example. If some of A is also unused, recalculate both alternatives rather than reusing this threshold.
Reproduce the example in Simuily
In the unit-price calculator enter A with price 3, quantity 750, unit g and one pack. Enter B with price 4, quantity 1.2, unit kg and one pack. This first comparison uses purchased quantities. For the utilisation scenario, change B’s quantity to 0.96 kg while keeping its purchase price. Do not enter several packs and also multiply the quantity by their count.
Check whether the products are comparable
Think about your actual consumption between shopping trips, storage space and the manufacturer’s storage instructions. Concentration, quality and serving size may make equal weights deliver different results. Add a genuinely necessary extra cost of using the larger pack, but do not assign it the whole cost of a shopping journey that would happen anyway.
What about offers and freezing?
Apply a discount to the total price before comparing again; an offer is not proof of a saving. Freezing is not proof that all contents will be used either. Product suitability, storage and whether you eventually use it still matter. An economic calculation does not extend food safety dates.
Choose using unit cost, usable quantity and the cash needed now. Save your assumptions, then change one at a time to see what actually drives the decision.