Compare the same product basis
A smaller sticker price does not always mean a cheaper purchase. Divide the amount you actually pay by the quantity you receive, then compare both packages in the same unit and currency. This guide uses arithmetic examples rather than live retail prices. It does not assume that two products have the same quality, ingredients or useful life.
Convert quantities before dividing
Suppose package A costs 3.60 for 750 g and package B costs 4.20 for 1 kg. Convert 750 g to 0.75 kg. A costs 3.60 ÷ 0.75 = 4.80 per kg; B costs 4.20 ÷ 1 = 4.20 per kg. B has the higher checkout price but the lower unit price. In the calculator, enter quantities 0.75 and 1 for a comparison per kilogram, or 750 and 1000 for a comparison per gram. Never compare 750 with 1 while treating both numbers as the same unit.
Calculate savings against a stated baseline
For an equal quantity of 1 kg, the difference is 4.80 − 4.20 = 0.60. Relative to A, B is 0.60 ÷ 4.80 × 100 = 12.5% cheaper per kg. Relative to B, A is 0.60 ÷ 4.20 × 100 ≈ 14.29% more expensive. These percentages use different denominators and are both valid when labelled correctly. Our comparison reports the reduction relative to the higher unit price.
Handle multipacks and usable contents
For six bottles containing 330 mL each, the total is 6 × 330 = 1980 mL, or 1.98 L. At a total price of 5.94, the price is 5.94 ÷ 1.98 = 3.00 per litre. Compare drinks by volume, identical individual items by count, and solids by mass when that fits the product. For canned food, decide whether drained or net weight reflects what you will use. Do not compare one product using drained weight and another using total weight without recognising the difference.
Apply an offer to the amount you really buy
If an offer gives three identical 500 g packs for 8.00, the relevant quantity is 1.5 kg and the unit price is 8 ÷ 1.5 ≈ 5.333333 per kg. Do not divide 8 by the quantity of just one pack. A loyalty discount is relevant only if you qualify. Include delivery charges or taxes consistently on both sides if they change your actual cost. A refundable deposit can be treated separately when you expect to recover it, but document that choice.
Round after comparing
Keep the unrounded unit prices during the comparison. A tiny difference can disappear when both values are displayed to two decimal places. A price per gram of 0.0048 equals 4.80 per kilogram; showing 0.00 per gram would hide useful information. The calculator displays additional precision for small unit prices. An estimate based on rounded package weights remains approximate even when the output contains many digits.
Check whether the lower unit price helps you
A larger pack can waste money if some contents expire or go unused. If a 2 kg pack costs 8.00 but only 1.5 kg is used, its effective cost per usable kilogram is 8 ÷ 1.5 ≈ 5.33. A smaller pack at 4.80 per kg could be better for that household. Storage, dietary needs and quality also matter. Unit price answers a narrow cost question; it does not decide which product is best.
Check the inputs before trusting the result
Prices must be non-negative and quantities greater than zero. To compare B, complete both of its fields. Use a consistent currency; this tool does not retrieve exchange rates. The calculation treats your inputs as numbers, not as a live offer, inventory check or legal assessment of a shelf label. Recalculate if a price, pack size or promotion changes.
Try the calculation
Maintained by Muhammad Bhutto · 2026-11-04 · Methodology