Compare pack sizes on one honest scale
Shelf prices are designed to be hard to compare: different pack sizes, different units, a multi-pack wrapped around smaller packs. Enter each product’s price, how many packs, and what is in each pack, and this page normalises everything to unit prices you can line up: per ounce and per pound, per fluid ounce and per litre, per item, per foot and per metre. Products are only compared within the same kind of measure, because a per-ounce winner between a drink and a detergent is a meaningless crown.
Quantity is what is in ONE pack; the packs field handles bundles (a 12-pack of 12 fl oz cans is 12 packs of 12 fl oz, or 1 pack of 144 fl oz: either way the total is the same, and the page multiplies it out).
Disclaimer: This calculator gives estimates for general information only. It is not financial, medical or other professional advice. Unit price compares quantity for money only; it says nothing about quality, concentration or how much of a product a job actually needs.
What this calculator does
It reduces every product to the price of one standard unit of what is inside, using exact conversion factors, and then ranks products that measure the same kind of thing. Weight is compared in grams under the hood and displayed per ounce and per pound; volume in millilitres, displayed per fluid ounce and per litre; count per item; length per foot and per metre. Multi-packs are multiplied out before the division, because the classic trap is a bundle whose per-pack quantity is quoted in a different unit from its rival. For every product that is not the cheapest of its kind, the verdict puts a dollar figure on the gap for the amount actually being bought, because “25% more per ounce” persuades nobody and “$0.90 extra for this much” does.
How to use it
- Copy the pack, not the shelf edge summary. Enter the net quantity printed on the packaging (drained weight where that is what is sold, for things packed in liquid), the number of packs in the bundle, and the price you would actually pay after any loyalty discount you genuinely hold. The unit price is only as honest as those three numbers.
- Watch the family lines. Results are grouped: weights with weights, volumes with volumes, counts with counts, lengths with lengths. A product alone in its family gets its unit prices but no verdict, because there is nothing legitimate to rank it against; that restraint is deliberate, and it is why a length of rope will never be declared better value than a litre of paint here.
- Bigger is usually cheaper per unit, and not always better. The unit price ignores spoilage, storage and cash tied up in a cupboard. The verdict’s “extra for the amount you are buying” line is deliberately framed on the purchase in front of you, not on a year’s supply: if the big pack will be half-wasted, its effective unit price is double the one printed here, and the smaller pack wins on the only terms that matter.
- Concentration is the invisible unit. Double-strength detergent, concentrated squash and high-yield ink all deliver more use per millilitre, so raw unit price overstates their cost per use. Where a product states doses, washes or pages per pack, compare on the per-use basis instead: divide price by uses, which the count family here does directly if you enter uses as the quantity.
- Unit price labels in stores use the same method (and in many places are required to), which makes this page a checking tool as much as a comparison tool: when the shelf label’s unit price cannot be reproduced from the pack’s own numbers, the label is wrong, the pack is mis-shelved, or the quantity you copied is the gross weight, and two of those three are worth a quiet word at the desk.
How it is calculated
- Total quantity = packs x quantity per pack, converted to the family base (grams, millilitres, items, inches) at exact factors: 1 oz = 28.349523125 g, 1 lb = 453.59237 g, 1 fl oz = 29.5735295625 mL, 1 gallon = 3,785.411784 mL, 1 ft = 12 in, 1 m = 39.3700787 in.
- Unit price = price / total quantity, expressed per display unit of the same family (for example per ounce = price per gram x 28.349523125).
- Best value = the lowest unit price within the family. Percent more = (unit price / best unit price – 1) x 100, computed on unrounded figures. Extra for this amount = (your unit price – best unit price) x your total quantity, the money saved on this purchase size by switching to the best.
- Rounding: unit prices display to the cent, or to four decimals below a dollar, since the differences that matter live there; percentages to two decimals.
Worked examples
The two bags. A 12 oz bag at $4.50 is $0.3750 per oz ($6.00 per lb). A 24 oz bag at $7.20 is $0.3000 per oz ($4.80 per lb) and takes the Best value mark: the small bag costs 25.00% more per ounce, which on the 12 oz you were about to buy is $0.90 extra. Unit pricing turns a shrug into a number.
The drinks shelf. A 12-pack of 12 fl oz cans at $10.99 holds 144 fl oz in total: $0.0763 per fl oz, $2.58 per litre. A single 2 litre bottle at $4.50 is $2.25 per litre and $0.0665 per fl oz, and wins: the cans cost 14.70% more per litre, about $1.41 extra across the pack. Convenience may still justify the cans; now it has a price, and you can decide whether it is worth it.
The hardware count. 100 screws at $6.00 is $0.0600 each; 240 at $12.00 is $0.0500 each, so the small box costs 20.00% more per screw. Unless 140 screws will live in a drawer for a decade, the big box is the rational buy, and the calculator’s job is done the moment that trade-off is visible.
Reading your results
Start with the verdict, then sanity-check it against the total quantities: a best-value win built on a quantity you mis-copied (net weight entered as gross, millilitres as fluid ounces) is the commonest failure, and the totals column exists so the error can be seen. Then read the extra-cost line rather than the percentage when deciding: percentages exaggerate small purchases and understate big ones, while the dollar line is exactly what changes hands. Finally, apply the two judgement calls no calculator can make for you: will the larger quantity actually be used before it spoils, separates or goes out of date, and is the cheaper-per-unit product the same strength and quality, or a diluted cousin wearing the same shelf label?
Limitations
- Quantity is not value. Quality, concentration, yield and suitability are outside the arithmetic. The page normalises amount for money, nothing else, and its disclaimer says so on the card.
- Cross-family comparisons are refused by design, including tempting ones like price per ounce of a solid versus a liquid; densities differ, jobs differ, and the ranking would be fiction.
- Prices are as entered. Deposit charges, delivery fees, and loyalty pricing you do not actually qualify for all bend the real unit price; enter the price that will leave your account.
- Display rounding can tie. Two products whose unit prices differ below the displayed precision are ranked on the unrounded figures; a photo-finish at the fourth decimal is a tie for every practical purpose, and the percent line will show it as a fraction of a percent.
Frequently asked questions
How is unit price calculated?
Total price divided by total quantity, after the quantity has been converted into one standard unit. A bundle is multiplied out first (packs times quantity per pack), the quantity is converted at exact factors into grams, millilitres, items or inches, and the price is divided by that. The result is then expressed in shopper-sized units: per ounce and per pound, per fluid ounce and per litre, and so on.
Why does the bigger pack sometimes lose?
Because pack size and pricing are set by different people with different aims: promotions often discount the mid-size, own-brand lines price the large pack for a different shelf, and multi-buy bundles can carry a worse unit price than the single under a banner that says otherwise. The arithmetic on this page assumes nothing about size; it divides, converts and ranks, which is precisely how the occasional upset gets caught.
Can I compare products in different units, like grams against ounces?
Yes: that is the normal case this page is built for. Any weight can be compared with any other weight and any volume with any other volume, across metric and imperial freely, because everything is converted to one base before dividing. What cannot be compared is different kinds of measure: weight against volume, or length against count, and the results keep those families separate so the mistake cannot happen quietly.
What about products sold by dose or use?
Enter the number of doses, washes, loads or pages as the quantity and “each” as the unit: the count family then prices one use, which is the comparison that matters for concentrated and high-yield products. It is also the fairest way to compare a small strong product against a large weak one, where the raw per-millilitre price points the wrong way.
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Method: total quantity (packs times quantity per pack) normalised to family base units at exact conversion factors; unit price as price over total quantity; ranking within measure families only, exactly as defined on this page. Last reviewed: 13 October 2026.