A larger pack is better value only if its lower unit price survives the discounts, delivery costs and waste that apply to your purchase. Start by comparing equal quantities, then check how much you will actually use. The examples below use hypothetical prices, not live shop offers.
Use the Unit Price Calculator on our homepage for the first comparison. It accepts grams, millilitres or item counts; it does not automatically estimate waste or convert between currencies.
Compare the same amount before comparing the bill
Suppose Pack A contains 500 g for $4 and Pack B contains 750 g for $5. Divide each price by its quantity, then multiply by 100 to compare the cost of 100 g.
| Pack | Price paid | Quantity | Price per 100 g |
|---|---|---|---|
| A | $4.00 | 500 g | $0.80 |
| B | $5.00 | 750 g | About $0.667 |
Pack B is about 16.67% cheaper per gram: (0.80 − 0.6666667) ÷ 0.80 × 100. This does not mean you save cash at checkout: you spend $1 more and receive 250 g more. If you only need a small quantity once, the lower total bill may matter more.
Find the point where waste removes the saving
Assume you use all 500 g of Pack A. To match its $0.008 cost per gram, you need to use $5 ÷ $0.008 = 625 g of Pack B. That leaves 125 g, or 16.67% of the larger pack, that could go unused before its effective price reaches the smaller pack’s price.
| Amount of Pack B used | Effective cost per 100 g used | Compared with fully used Pack A |
|---|---|---|
| 750 g | About $0.667 | Cheaper |
| 625 g | $0.80 | Equal |
| 600 g | About $0.833 | More expensive |
The general calculation is effective unit price = total price ÷ quantity actually used. If both packs have waste, adjust both quantities. In the homepage tool, you can enter expected usable grams instead of labelled grams to compare this scenario, but keep your original quantities separately: the result then describes usable quantity, not shelf unit price.
A coupon can reverse the winner
If a $1 coupon applies only to Pack A, its price falls to $3. Its new cost is $0.60 per 100 g, below Pack B’s roughly $0.667. Enter the price you will actually pay after an eligible discount. Do not apply a coupon to both packs unless its terms allow that, and do not treat a future reward as an immediate price reduction without saying so.
Handle multipacks and mixed units correctly
Six bottles containing 250 mL each provide 1,500 mL. At $4.50, the multipack costs $0.30 per 100 mL. A 1 L bottle for $2.80 contains 1,000 mL and costs $0.28 per 100 mL. The single bottle is cheaper per volume despite the multipack label.
Multiply bottle size by bottle count before entering quantity. Convert litres to millilitres and kilograms to grams. Do not compare fluid ounces with weight ounces as though they measure the same thing. For the reasoning behind consistent comparison units, see NIST’s unit-pricing guide.
Check whether the products are genuinely comparable
- Concentration: a smaller concentrated product may provide more uses. If the label gives comparable usage counts, compare cost per use with the Items option.
- Delivery: include an unavoidable charge when comparing complete purchase alternatives. Do not allocate an entire shared basket delivery fee to one pack unless that is the decision you are modelling.
- Budget and storage: a lower unit price does not create extra cash or shelf space.
- Usability: compare the amount you can use under the product’s storage instructions. This calculation does not establish food safety or shelf life.
Make a purchase decision in three checks
- Compare final prices using the same measurement unit.
- Repeat with realistically usable quantities if waste could change the result.
- Choose the option that fits your budget, storage and required quality.
For ingredients bought for a business, continue with our batch-cost versus unit-cost example to separate purchase savings from production costs. The Cost Calculator adds fixed expenses and other charges to a batch; a cheap ingredient alone does not establish a profitable selling price.