Unit price comparison calculator

Enter two package prices and quantities to find which option costs less for the same amount.

Item A: package price
Item A: quantity
g
Item B: package price
Item B: quantity
g

Better value

Item B is better value

Unit price A300 / kg
Unit price B260 / kg
Difference40 / kg
Savings13.33 %

Amounts use the same currency as the prices entered.

How the unit price comparison works

Two differently sized packages compared on the same unit-price scale

The calculator converts two package prices to the same kilogram, litre, pound, US gallon or single item, then identifies the lower unit price.

Put both packages on one basis

Choose the unit printed on both packages and enter each full package price and quantity. If the labels use different units, convert one first: 1 kg is 1000 g, 1 lb is 16 oz, 1 L is 1000 ml, and 1 US gallon is 128 US fluid ounces.

The calculation uses one simple relationship:

U=P⋅BQ\displaystyle U=\frac{P\cdot B}{Q}

UU is the unit price, PP is the package price, QQ is the package quantity, and BB is the base quantity. The base is 1000 for grams and millilitres, 16 for ounces, 128 for US fluid ounces, and 1 for units already entered as kg, lb, L, US gal or items.

Use one currency for both prices. The calculator does not need to know whether the numbers are dollars, euros or another currency because it never converts money; every monetary result stays in the currency you entered.

The winner is the item with the lower normalized price. Savings are measured against the more expensive unit price, so a result of 20% means the cheaper option costs one fifth less for the same quantity.

Examples from the shelf

Rice by weight. Item A costs 150 for 500 g and item B costs 260 for 1000 g. Their prices are 300 and 260 per kg. Item B is cheaper by 40 per kg, or 13.33% relative to item A.

Juice by volume. A 1000 ml bottle costs 90 and a 500 ml bottle costs 45. Both equal 90 per litre. The larger bottle has no unit-price advantage, so size, storage and likely use can decide the purchase.

Batteries by count. Twelve batteries cost 720, while eight cost 500. The unit prices are 60 and 62.50. The twelve-pack is cheaper by 2.50 per battery, a 4% saving, provided the batteries are otherwise comparable.

Imperial package sizes. A 16 oz bag for 8 costs 8 per lb. A second 16 oz bag for 9 costs 9 per lb. The first is 1 per lb cheaper, or 11.11%. Both quantities must use ounces before this comparison.

A low unit price is only the first filter

Enter the amount actually paid after a discount. For a multipack, add the quantities in all included packages and use the full bundle price. Delivery or service charges belong in the price only when they differ between the two offers and are unavoidable.

Compare equivalent goods. Price per litre cannot fairly compare a concentrate used at 20 ml per dose with a ready-to-use liquid unless you first calculate the number of usable doses. Pizza prices should be compared by area, not diameter, because the amount of food grows with the square of the radius.

A large package can have the lowest displayed unit price and still waste money if part of it expires or requires costly storage. Quality, ingredients, warranty, refillability and the amount you will actually use remain outside this calculation.

Displayed values are rounded to at most two decimal places, while the comparison uses the unrounded finite numbers. Very small display differences can therefore appear equal after rounding; decisions that depend on fractions of a cent should use the source prices and quantities at their full precision.

Questions about unit prices

These answers cover the common cases where package labels, promotions or product differences make a quick division less obvious.

How do I compare 500 g with 1 kg?

Choose grams and enter 500 for the first quantity and 1000 for the second. Alternatively, choose kilograms and enter 0.5 and 1. Both methods produce the same price per kilogram.

Should I enter the price before or after a discount?

Use the amount you will actually pay. If a package marked 80 has a 25% discount, enter 60.

Can I compare multipacks?

Yes. Add the total number, mass or volume in the pack and enter the full bundle price. Three 500 ml bottles contain 1500 ml.

Why are two packages shown as equal?

Their unrounded prices may be equal or close within numerical tolerance. When the displayed values match, compare size, freshness, quality and likely waste instead.

Can the prices use different currencies?

No. Convert one price first so both use the same currency. This calculator compares ratios and has no exchange-rate data.

Does the cheaper unit price always mean I should buy it?

No. It answers only the price-for-equal-quantity question. Usable yield, quality, storage, expiry and the quantity you need can change the sensible choice.

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