Unit Price Calculator
Which pack is the better buy? Enter the price and size of each and see the price per kg, litre or item, ranked. Advanced adds multipacks, deals, coupons and your monthly saving.
Right for water, milk and most drinks. Not for oil, honey or powders.
How your unit prices are worked out
Price per unit = price you pay ÷ how much you get, with every pack turned into the same unit first.
- 1
Same unit for all
Big pack: 1.2 kgSmall pack: 500 g= 0.5 kg
- 2
Price you pay
Big pack: 9.60Small pack: 4.50no deals
- 3
Price per kg
9.60 ÷ 1.2= 8.004.50 ÷ 0.5= 9.00
- 4
The better buy
Big pack wins8.00 vs 9.0011.11% cheaper
Read more: the formula, worked example, deals and unit tables
The formula
amount you get = packs × size, turned into one unit (g, ml, m or items)
unit price = price you pay ÷ amount you get
price per kg = unit price per g × 1,000 (per 100 g: × 100)
% cheaper = (1 − best unit price ÷ dearest unit price) × 100
saving a month = (dearest − best unit price) × how much you use a month
Worked example
A small pack is 500 g for 4.50 and a big pack is 1.2 kg for 9.60.
- Small: 500 g = 0.5 kg, so 4.50 ÷ 0.5 = 9.00 a kg.
- Big: 9.60 ÷ 1.2 = 8.00 a kg.
- The big pack is the better buy: 1 − 8.00 ÷ 9.00 = 0.1111, so it is 11.11% cheaper. Looked at the other way, the small pack costs 12.5% more per kg.
- On the same 500 g, the big pack costs 0.5 × 8.00 = 4.00 instead of 4.50, a saving of 0.50. The small pack would have to cost 4.00 or less to match it.
- If you use 2 kg a month: 2 × 9.00 = 18.00 against 2 × 8.00 = 16.00, so you save 2.00 a month, or 24.00 a year.
Multipacks and deals
The calculator counts what you actually take home for what you actually pay.
- Multipack: 3 × 500 g for 6.00 is 1.5 kg, so 6.00 ÷ 1.5 = 4.00 a kg.
- Buy X get Y free: buy 2 get 1 free on 400 g packs at 3.00 gives 3 packs (1.2 kg) for 6.00, which is 5.00 a kg instead of 7.50.
- Multi-buy: "3 for 5" on 250 ml bottles is 750 ml for 5, which is 6.67 a litre.
- % off: 25% off 2.00 is 1.50.
- Coupon: money off is taken once from what you pay (after any deal), e.g. 1.00 off a 5.00 bag of 1 kg is 4.00 a kg.
A deal only saves money if you will use it all before it goes off. Use the monthly amount in Advanced to check.
Unit conversions used
| Unit | Equals |
|---|---|
| 1 oz | 28.3495 g |
| 1 lb (16 oz) | 453.592 g |
| 1 US fl oz | 29.5735 ml |
| 1 UK fl oz | 28.4131 ml |
| 1 US pint / quart | 473.176 ml / 946.353 ml |
| 1 UK pint | 568.261 ml |
| 1 US gallon | 3.78541 L |
| 1 UK gallon | 4.54609 L |
| 1 ft / 1 yd | 0.3048 m / 0.9144 m |
| 1 dozen | 12 items |
Tips for the shelf
- Shelf labels in many countries show a unit price, but check the unit: one label may say per 100 g and the next per kg.
- For toilet paper and kitchen rolls, compare per sheet, not per roll, since roll sizes differ.
- For washing powder and pods, compare per load (wash), not per kg.
Common questions
How do I work out the unit price?
Divide the price by how much is in the pack, after turning every pack into the same unit. 500 g for 4.50 is 4.50 ÷ 0.5 kg = 9.00 a kg. 1.2 kg for 9.60 is 9.60 ÷ 1.2 = 8.00 a kg, so the big pack is the better buy, 11.11% cheaper.
Is the bigger pack always cheaper?
No. Big packs are often cheaper per kg, but not always, and a deal on the small pack can beat them. Shops sometimes price the large size higher per unit. Always compare the price per kg, litre or item, which is what this calculator does for up to six products.
How do I compare ounces with grams?
Turn both into the same unit. One ounce is 28.35 g and one pound is 453.59 g, so 16 oz is 453.59 g. Pick any unit for each product here and the calculator converts them for you before comparing.
How do I work out the unit price with a buy one get one free deal?
Count what you actually get for what you pay. Buy 2 get 1 free on 400 g packs at 3.00 means 1.2 kg for 6.00, which is 5.00 a kg instead of 7.50. For "3 for 5" you get three packs for 5, so divide 5 by the total of the three packs.
Can I compare milk in litres with a powder in grams?
Weight and volume can only be compared if you know how heavy the liquid is. For water, milk and most drinks, 1 ml weighs about 1 g, so in Advanced you can switch on "Treat 1 ml as 1 g". For oils, syrups or powders this is not accurate.
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