How to compare prices
- Type the price and size of each pack, and pick the unit printed on it (grams, ounces, litres, items…).
- Compare up to four products. You can mix units of the same kind, such as grams and pounds, or millilitres and fluid ounces.
- The best value is highlighted, and each other product shows how much more it costs per unit.
How it's calculated
Every size is turned into the same small unit (grams, millilitres or items), then the price is divided by it. That gives a fair price per unit, whatever size the pack is.
Price per unit = price ÷ size (in the same unit)
How much more = (this price per unit ÷ cheapest price per unit − 1) × 100
1 oz = 28.349523125 g 1 lb = 453.59237 g
1 US fl oz = 29.5735295625 ml 1 UK fl oz = 28.4130625 ml
Worked examples
500 g for $3.49 → $6.98 per kg
1 kg for $6.29 → $6.29 per kg ← best value; the small pack costs 11% more per kg
12 US fl oz for $1.29 → $3.635 per litre
2 litres for $2.49 → $1.245 per litre ← best value (the can costs 192% more per litre)
Frequently asked questions
Is the bigger pack always cheaper?
No. Multi-buy deals and offers on small packs often make the smaller size cheaper per unit, which is why comparing the unit price is worth doing. And a cheaper pack only saves money if you'll use it all before it goes off.
Shops already show unit prices. Why use this?
Shop labels sometimes use different units for different products (per 100 g on one, per kg or per item on another), and online prices often don't show one. Typing the prices here puts them all on the same footing.
Why can't I compare grams with millilitres?
Weight and volume aren't the same thing: a litre of oil weighs less than a kilogram. Compare products measured the same way.