How to use it
- Type one product on each line in Products, one per line: name; price; quantity per pack; unit; pack count.
- Enter the Amount you buy in kilograms, litres or pieces, the unit your products use.
- Read the Lowest unit price and the Cheapest product, then the ranking table.
- Check Money saved on the amount to see what the cheapest choice saves for the amount you buy.
How the unit price is calculated
The unit price is the price of one unit of measure of a product: one kilogram, one litre or one piece. Wikipedia defines unit price as the price for a single unit of measure of a product sold in more or less than that single unit. A 500 ml bottle at 6.50 costs 13.00 per litre, because 6.50 divided by 0.5 litres is 13.00.
The pack count multiplies the quantity of one pack: six packs of 500 ml hold 3 litres. Grams are divided by 1,000 to get kilograms, and millilitres by 1,000 to get litres.
Total amount = quantity per pack × pack count
Unit price = price ÷ total amount (kilograms, litres or pieces)
1 kg = 1,000 g and 1 l = 1,000 mlHow the ranking and the saving are calculated
The products are ranked from the lowest unit price up. The saving on your amount is the difference between the most expensive and the cheapest unit price, multiplied by the amount. The percentage in the table is how much cheaper the cheapest product is than that row's product: the difference divided by that row's unit price.
Saving on the amount = (most expensive unit price − cheapest unit price) × amount
Cheaper by (%) = (unit price − cheapest unit price) ÷ unit price × 100What this comparison does not include
- VAT, deposits and taxes. Whether the shelf price includes them depends on the shop; add them to the price you type when they change what you pay.
- Discounts, coupons and loyalty points, which change the price you pay. Type the discounted price, or use the successive discount calculator.
- Quality, brand, taste and how long the product keeps. The figures compare price and amount only.
- Weights and volumes in one list. A kilogram cannot be compared with a litre, so each list uses one measure.
Worked example: three olive oil packs, for 3 litres
Prices are in dollars in this example. The 500 ml bottle at 6.50 costs 13.00 per litre. The 1 l bottle at 11.90 costs 11.90 per litre. The 3 l tin at 31.50 costs 10.50 per litre, so it is the cheapest.
For 3 litres the tin costs 31.50, the 1 l bottle 35.70 and the 500 ml bottle 39.00. Against the 500 ml bottles the tin saves 7.50, which is 19.23% of what 3 litres cost in those bottles.
| Product | Unit price per litre | Cost for 3 litres |
|---|---|---|
| Olive oil 3 l tin | 10.50 | 31.50 |
| Olive oil 1 l | 11.90 | 35.70 |
| Olive oil 500 ml | 13.00 | 39.00 |
Frequently asked questions
Why is the smallest pack not always the cheapest per unit?
A small pack can have a low shelf price and still cost more per kilogram or litre. Compare the unit price, which is the price of the same amount, because a bigger pack can cost more in total and still be cheaper per litre.
Can I compare grams with kilograms in one list?
Yes. Grams and kilograms are both weights, and millilitres and litres are both volumes, so they can share a list. A weight and a volume cannot share one list, because a kilogram of one product cannot be compared with a litre of another.
Does the calculator include VAT, deposits or discounts?
No. It uses the prices you type. If a VAT, deposit or discount changes the amount you pay, type the price you actually pay before you compare.
What does the money saved on the amount mean?
It is the difference in unit price between the most expensive and the cheapest product, multiplied by the amount you buy. It is how much less you pay for that amount if you choose the cheapest product.
Is the list of products I type sent anywhere?
No. The calculation runs in your browser, and nothing you type is sent to us.
Sources
Figures and text last checked on Tuesday, November 10, 2026.