Compare different pack sizes
Shelf prices are hard to compare when the packs are different sizes. Unit price turns every offer into the same yardstick, such as price per kilogram, per litre or per item. Pick what you are comparing (weight, volume, count or area), enter each offer, and the calculator ranks them from the lowest to the highest unit cost. You can compare up to five offers at once, each with its own pack count, size and unit.
Unit-price formula
Unit price = adjusted offer price ÷ total quantity. The adjusted price is the price of the whole offer after any percentage discount, plus any fixed added cost: price × (1 − discount ÷ 100) + added cost. The total quantity is packs × size per pack, converted to a common unit. A 500 g pack at $6 is 6 ÷ 0.5 = $12.00 per kg.
Price per ounce, and ounce versus fluid ounce
An ounce of weight and a fluid ounce of volume are different units, so they are kept in separate comparison types and cannot be mixed. Weight uses the exact international definitions (1 oz = 28.349523125 g, 1 lb = 453.59237 g) and volume uses the US fluid ounce (29.5735295625 mL). A 32 oz pack at $6.38 is exactly 2 lb, or $3.19 per lb. Converting between weight and volume would need a density, so the calculator does not do it.
Multipack and discount example
Offer A is one 500 g pack for $6. Offer B is two 300 g packs for $7.20 with 10% off and a $0.50 bag fee. B costs 7.20 × 0.9 + 0.50 = $6.98 at the checkout for 0.6 kg, so $11.63 per kg against $12.00 for A. B is about 3.06% cheaper per kilogram, even though you pay more at the till. A multipack is not always cheaper: enter the real prices and let the unit cost decide.
When coupons stack, compare ordered coupons to get the real checkout price before you enter it as an offer.
Include shipping and tax amounts
Use the added-cost box for any fixed amount you pay for the whole offer, such as delivery, a deposit or a tax amount you already know. Enter it as money, not a rate. To model a buy-one-get-one offer, enter the total quantity you receive and the total price you pay. All offers share one currency label; the calculator never converts currencies. Shipping parcels yourself? Check dimensional shipping weight before you price delivery into an offer.
Unit cost versus checkout spending
The lowest unit price is not always the best choice. A big pack can cost more today, take more space, or go to waste before you use it, and the calculator cannot judge quality. For flooring, compare tile cartons per square metre here after estimating how many boxes you need with the tile calculator; area offers in m² and ft² are converted exactly. For decorating, work out how many paint cans to buy, then compare can sizes here as volume offers in litres or gallons. For example 1.44 m² for $72 is $50.00 per m², while 16 ft² for $80 is $53.82 per m². Businesses buying stock can carry the unit cost into the margin and markup calculator to set a selling price, or into the break-even calculator as a variable cost.
Once a discount is applied, you may also want to split a bill with tax and tip and see the final amount a group pays.
Shelf prices abroad often include value-added tax: compare prices including VAT on a like-for-like basis before you compare sizes.
In the United States tax is added at the till, so compare unit prices after sales tax when only some items are taxed.
Buying abroad? You can compare currency conversion after fees before comparing foreign unit prices.
FAQ
How do I calculate unit price?
Divide the price you pay by the quantity you get, in the same unit for every offer. Include discounts and added costs in the price first.
Is a multipack always cheaper?
No. Some multipacks cost more per unit than a single large pack. Compare unit costs rather than assuming.
Is an ounce the same as a fluid ounce?
No. An ounce measures weight and a fluid ounce measures volume. This calculator keeps them in separate comparison types.
How are discounts and added costs treated?
The percentage discount is applied to the whole-offer price, then the fixed added cost is added once for that offer.
Can I compare price per square metre and square foot?
Yes. Choose Area, enter each offer in m² or ft², and the calculator converts with 1 ft² = 0.09290304 m².
Why does a low unit price cost more at checkout?
Because you buy more units. A lower price per unit on a bigger offer can still mean a bigger bill today.