Compare equal quantities before comparing labels
A pack price tells you the amount due for that pack. A unit price tells you the rate for an equal quantity of product. A larger pack can have the lower rate while requiring a larger immediate payment, so these two questions should remain separate.
In the unit price calculator, 500 g for 3.50 works out at 7.00/kg. One kilogram for 6.00 is cheaper by 1.00/kg, approximately 14.29%. The calculation does not mean that choosing the larger pack reduces that particular checkout bill by 1.00.
Make the amount match the price
For six bottles sold together, use the contents of all six bottles and the price of the complete multipack. If only one bottle is priced, enter one bottle’s amount. Exclude the container mass when comparing the product itself.
For diluted or concentrated goods, consider whether the useful result is comparable. A litre of concentrate and a litre of ready-to-use liquid can have different yields. The tool compares entered physical quantities; it cannot decide the amount of usable cleaning solution, food or paint they produce.
Keep measurement families distinct
Weight, liquid volume and item count are separate families. An ounce of weight is not a fluid ounce. A US gallon and an Imperial gallon are also different volumes. The selector names identify these distinctions rather than hiding them behind an ambiguous label.
If two products are sold in different families, find suitable product-specific information before trying to compare them. A density assumption may be appropriate in some contexts, but it is deliberately not invented by this tool.
Check value beyond the numerical winner
A low unit rate can be poor value if half the contents expire unused. Storage space, quality, concentration, returns and shipping can also affect the practical choice. Adjust the prices consistently for known charges, then treat the unit result as one input to the decision.
Use the percentage calculator to inspect a relative price change over time. For resale pricing, the margin and markup calculator answers a different question: how cost and selling price relate to profit.