How to compare unit prices
- Enter the Item A price, its amount and its unit, such as 3.99 for 500 grams.
- Do the same for item B, and item C if you’re comparing three. The units can differ, such as 500 g against 1 kg or 12 oz against 1 lb, as long as they measure the same thing.
- Read which item is the better buy, each one’s price per 100 g, kg, oz or litre, and how much cheaper the winner is.
Price per 100 grams instead of per gram
Per-gram prices are tiny numbers like 0.008 that are hard to compare at a glance, so the calculator shows prices the way shelf labels do: per 100 g and per kg for metric weights, per oz and per lb for imperial ones, and per 100 ml and per litre for drinks. The unit of item A decides which.
| Pack | Price | Amount | Per 100 g | Per kg |
|---|---|---|---|---|
| A | 3.99 | 500 g | 0.798 | 7.98 |
| B | 6.49 | 1 kg | 0.649 | 6.49 |
Pack B is 18.7% cheaper per 100 g. The better buy and the percentage are the same whichever unit you compare in.
Things a unit price doesn’t tell you
The cheapest per unit isn’t always the best buy. Food that spoils before you finish it, a big pack you have no room to store, or a bulk tub you’ll need to pay for all at once can all cancel the saving. For cleaning products and drinks, check the concentration too: a concentrate that needs diluting can work out cheaper than a ready-to-use bottle that looks cheaper per litre.
The same sum works for anything sold by quantity: price per sheet of toilet roll, per wash for detergent, per tablet for vitamins or per GB for storage. Choose items or any other unit, and use the same one for every item.