Unit price calculator
The grocery-aisle question: is the big one actually cheaper? Price and quantity for each option, winner announced.
Beating the shelf tag at its own game
Most US stores print a unit price on the shelf tag, so why type it in here? Because the tags cheat, not always deliberately. On the same shelf you will find one brand priced per ounce, the neighbor priced per 100 count, and the store brand per roll. The moment the units differ, the printed tags cannot be compared, and that moment is exactly when this calculator earns its keep: enter each item's real price and its quantity in the same unit, and the comparison becomes honest again.
Pick your unit with intent. For anything concentrated, detergent, dish soap, coffee, price per load or per brewed pot beats price per ounce, because a double-strength formula in a smaller bottle can lose the per-ounce contest while winning on cost per use. The quantity field takes any number you define, so "loads per bottle" is a perfectly legal input.
And read the "Cheaper by" percent with a cold eye. A 3% gap on paper towels is noise; buy whichever fits your cabinet. A 25% gap on something you buy weekly is a real annual sum. The percent is measured against the more expensive option, so it answers the question "what am I overpaying by if I grab the loser".
A grocery aisle example
Two packs of the same paper towels: Option A is 12 rolls for $8.99, Option B is 24 rolls for $16.49. Per-unit prices come out to 74.9¢ per roll for A and 68.7¢ per roll for B. The calculator declares Option B the better value, cheaper by 8.3%. Concretely, buying two of the small packs to match the big one would cost $17.98 against $16.49, a $1.49 penalty for the smaller boxes. Bulk won this round, but rerun it every time: "bulk traps," where the jumbo size quietly costs more per unit, show up often enough that the check pays for itself.
What the calculator computes
Each option's unit price is simply its price divided by its quantity. Unit prices below a dollar display in tenths of a cent, since grocery decisions often hinge on fractions of a cent, and prices of a dollar or more display in dollars to three decimals. The winner is whichever unit price is lower, and the savings percent is the gap divided by the higher unit price, rounded to one decimal. If the two work out identical to within rounding, it says "Dead even" rather than manufacturing a winner. Quantities must be above zero; a zero quantity has no unit price and the tool refuses to guess.
What it cannot judge
Unit price is necessary but not sufficient. The calculator has no idea whether you will finish the 24-pack before it goes stale, whether the big box fits your apartment, or whether the cheaper brand is worse at its actual job. It also assumes both quantities are in the same unit, and it will happily compare ounces against grams without warning you; convert first when labels mix systems. Coupons and loyalty discounts should be applied to the price before you enter it, since a discounted small size beats a full-price large one more often than shelf tags suggest.
Frequently asked questions
What is a unit price?
Price divided by quantity: cost per ounce, per roll, per load. It is the only fair way to compare a 12 oz jar at $3.49 against an 18 oz jar at $4.89 (29.1¢ vs 27.2¢ per ounce; the big jar wins).
Do the two options need the same units?
Yes, compare ounces to ounces or grams to grams. If one label is metric and the other imperial, convert one first; the unit converters on this site handle that.
Is bigger always cheaper per unit?
Usually but not always. Stores count on the assumption; "bulk traps" where the large size costs more per unit are common enough that checking pays for itself.