Ladabo

Cost Per Unit Calculator

Compare three package sizes and see which is actually cheaper.

€

Grams, millilitres, sheets, tablets — anything, as long as all three use the same unit.

€
€

Leave the price at zero if you are only comparing two.

Results update as you type. Nothing is sent anywhere.

Best value —
Option A per unit —
Option B per unit —
Option C per unit —
Cheaper than the next best by —
Saved per 100 units — Against the next best option.

How this is worked out

One division per option, then compare:

unit price = price ÷ quantity

Everything must be in the same unit. A 500 g bag against a 1.2 kg bag means entering 500 and 1200, not 500 and 1.2. Mixing units is the only way to get a wrong answer here, and it produces one that looks entirely plausible.

Shelf labels often show a unit price already, but they are inconsistent about which unit they use — per 100 g on one label, per kilo on the next — and promotions frequently show the pre-discount unit price. Working it out yourself takes ten seconds and is reliable.

The output worth watching is cheaper by. Bulk is usually better value, but often only by two or three per cent, which is not worth buying more than you will use. Occasionally the big pack is worse, especially when the small one is on offer.

A worked example

  • A: 2.49 for 500 g → 0.00498 per gram
  • B: 3.99 for 900 g → 0.00443 per gram
  • C: 5.99 for 1500 g → 0.00399 per gram

C wins, and it is 9.9% cheaper per gram than B — about 0.44 saved per 100 g.

But now suppose it is something perishable and you will throw away a third of the big pack. Effectively you paid 5.99 for 1000 usable grams, which is 0.00599 per gram — the worst of the three. The unit price only tells you the truth about the portion you actually use.

What this doesn't cover

  • Same unit for every option. Convert kilos to grams and litres to millilitres before you enter them.
  • Multi-buy offers need converting first: "3 for 2" on a 500 g pack is three packs at the price of two, so enter twice the price against 1500 g.
  • Waste is not modelled. For perishables, enter the quantity you will realistically use rather than the quantity printed on the pack.
  • Concentrated products need converting to made-up quantity to compare fairly with ready-to-use ones.

Common questions

Why does the shelf label sometimes disagree with this?

Usually because the label has not been updated for a promotion, or because it uses a different base unit than you assumed. Where they disagree, trust the arithmetic you can see.

Is bulk always cheaper?

No, and it is worth checking rather than assuming. Small packs on promotion regularly beat the large one, and some products are priced higher per unit in the large size precisely because shoppers assume otherwise.

How do I compare a subscription against a one-off purchase?

Work out the quantity the subscription delivers over a year and the total you pay over that year, then treat it as one option. That also forces you to notice how much it actually delivers, which is usually the part people have not looked at.

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