Last updated: 2026-06-03

Understanding Unit Price Comparison

A unit price comparison calculator divides the total price of each product by its quantity and converts both to the same base unit — grams for mass, milliliters for volume — so you can compare them on equal footing. Anyone who has stood in a supermarket aisle wondering whether the 400 g box or the 750 g bag is the real bargain will find this calculator useful.

How to use this calculator

1. Measure by — Choose whether the items are sold by weight, by volume, or by count. This sets the measurement family for both items at once, so the comparison can never slip into mismatched units.
2. Item A — Enter the price, the quantity number printed on the label, and the unit. Within a weight comparison you can still mix g and oz; within a volume comparison you can mix L and fl oz.
3. Item B — Do the same for the competing product.
4. The calculator shows the cost per base unit for each item, which one is the better value, the percentage savings, and the absolute price difference per unit.

Worked example

You are choosing between two packages of pasta:

• Item A: $1.79 for 340 g
• Item B: $2.49 for 500 g

Enter price and quantity, select "g" for both, and the calculator shows:

• Unit price A = $1.79 / 340 = $0.00526 per gram
• Unit price B = $2.49 / 500 = $0.00498 per gram

Item B is the better deal by about 5.3% — or roughly $0.00028 per gram. Over a 340 g serving, that is about $0.10 saved.

Why this formula works

Dividing price by quantity in a common unit produces a ratio — cost per gram, cost per mL — that strips away package-size differences. Once both products share the same denominator, the lower number wins. The savings percentage shows the relative gap: (pricier − cheaper) / pricier, which expresses how much more per unit you pay for the worse deal.

Converting between unit families (oz to g, fl oz to mL) uses fixed, internationally agreed conversion factors:

• 1 oz = 28.349523125 g
• 1 lb = 453.59237 g
• 1 fl oz (US) = 29.5735295625 mL
• 1 L = 1,000 mL, 1 kg = 1,000 g

Common pitfalls when comparing prices

Ignoring perishability. A 2 kg bag of flour may be 15% cheaper per gram, but it is only a bargain if you can use it before it goes stale. Calculate whether the savings outweigh the waste risk.

Store-brand vs. name-brand gaps. Unit price neutralizes brand packaging, which is why store-brand products often look more competitive once the math is visible. The calculator does not include quality differences — you make that call.

Sale prices that flip the ranking. A smaller size on promotion can beat the "economy" size. Always check the actual shelf price, not the regular price, before entering numbers.

Different unit systems on the label. A US product may list 12 fl oz while an imported equivalent lists 355 mL. Select "fl oz" and "mL" respectively; the calculator converts both to milliliters.

Loyalty-card or multi-buy discounts. If a deal requires buying two or three units, enter the combined price and combined quantity to get the effective unit price.