Unit Price Calculator

What this calculator answers

Which of several sizes, brands or multipacks costs the least for what you get, and how much more each of the others costs. Enter each package the way its label reads, such as $4.99 for 6 × 16.9 fl oz, and the calculator puts every item on one unit (per ounce, pound, 100 g, fluid ounce, liter, sheet or item), ranks them, marks the best value and shows each other item’s percentage and dollars more per unit. Items that can’t be measured against each other, such as a jar sold by weight and a bottle sold by volume, are ranked in separate groups with the reason. If you say how much you need, it also works out the cheapest way to buy that amount in whole packs.

How to use it

Each row is one item. Press Add item for up to 10, or Paste rows to bring in a list copied from a spreadsheet.

• Name (optional): anything that tells the items apart, such as “Store brand” or “Family size”. Unnamed rows are called Item 1, Item 2 and so on.
• Price: what the whole pack costs, in dollars.
• Pack count: how many packages come together, such as 6 for a 6-pack. Leave it blank for a single package.
• Size and Unit: the net contents of one package, from the label. The unit list marks which ounces weigh (oz) and which measure volume (fl oz), and has counts such as items, sheets, rolls, loads and servings.
• Coupon or discount (optional): dollars off (1 for $1 off) or a percentage (20%), taken off that item’s price.
• Compare per: Automatic uses the unit most of your items are labeled in. Pick another, such as per pound or per liter, to match a shelf tag.
• Amount you need (optional) and its unit: how much you will use before it spoils or you tire of it. The calculator then prices whole packs of each item for that amount.

Results update as you type. The Try buttons load the cases below: a cereal aisle with 24 oz needed, a tie, the ounce trap, a coupon and toilet paper by the sheet. To compare the same products at two stores, press Save for comparison, change the prices and save again.

How to calculate unit price

Divide the price by the quantity, with every item’s quantity in the same unit.

$$\text{unit price} = \frac{\text{price} - \text{discount}}{\text{pack count} \times \text{size of one package}}$$

• The price is for the whole pack, and the discount is any coupon or sale amount taken off it.
• The quantity is the pack count times the size of one package, converted to the comparison unit. For a price per 100 g or per 100 sheets, multiply the result by 100.
• To see how much more an item costs than the cheapest, divide its unit price by the lowest one and subtract 1: $(\text{unit price} \div \text{lowest} - 1) \times 100$ gives the percentage.

Worked example: a 2-liter bottle, a 12-pack and a 6-pack

A 2-liter bottle of soda costs $2.29, a 12-pack of 12 fl oz cans $7.49 and a 6-pack of 16.9 fl oz bottles $4.99. Two of the three are labeled in fluid ounces, so that is the unit.

1. Quantities in US fluid ounces: 2 L = 2,000 mL ÷ 29.5735 mL = 67.628 fl oz; 12 × 12 fl oz = 144 fl oz; 6 × 16.9 fl oz = 101.4 fl oz.
2. Unit prices: $2.29 ÷ 67.628 = $0.0339 per fl oz; $4.99 ÷ 101.4 = $0.0492 per fl oz; $7.49 ÷ 144 = $0.0520 per fl oz.
3. The 2-liter bottle is the best value. The 6-pack costs $0.049211 ÷ $0.033862 − 1 = 45.3% more per fluid ounce, and the 12-pack 53.6% more.
4. At the bottle’s rate, the 144 fl oz in the 12-pack would cost 144 × $0.033862 = $4.876, so the 12-pack would need to be $4.87 or less to match it. The 6-pack would need to be $3.43 or less.

Per liter the order is the same: $1.15 for the bottle, $1.66 for the 6-pack and $1.76 for the 12-pack. NIST’s unit pricing guide uses this very pairing, 2 L bottles and 12 fl oz cans, to show why a store should price them in one unit.

Multipacks, “2 for $5” and coupons

Enter a multipack as the pack count and the size of one package, the way the label’s quantity statement is written (6 × 16.9 fl oz = 101.4 fl oz). If a label gives only the total, leave the pack count blank and enter the total as the size.

• “2 for $5”: enter $5 as the price and 2 as the pack count. The unit price is the same whether you think of it as one deal or two packages at $2.50.
• Buy one, get one free: enter the price of one and 2 as the pack count.
• Coupons and percent-off sales: enter them under Coupon or discount on the item they apply to.

A coupon can reorder the shelf. A 12 oz bag of coffee at $8.99 is $0.749 per oz, the most of three sizes, but with a $2 coupon it is $6.99, or $0.583 per oz. That beats a 40 oz canister at $23.99 ($0.600 per oz, 3.0% more) and a 24 oz bag at $14.49 ($0.604 per oz, 3.6% more).

Comparing price per ounce, pound, liter or item

Any unit of the same kind gives the same order; only the numbers change. The calculator picks the unit most of your items are labeled in, the rule NIST’s guide gives stores for choosing a category’s unit, so a comparison doesn’t mix metric and US units. Grams compare per 100 g and milliliters per 100 mL. Sheets and items switch to per 100 when every pack holds at least 100, so toilet paper at $0.00399 per sheet reads as $0.399 per 100 sheets.

Conversions are exact: 16 oz = 1 lb = 453.59237 g, and 128 US fl oz = 1 US gallon = 3.785411784 L. That is why a 16 oz jar at $3.20 and a 2 lb jar at $6.40 come out as a true tie at $0.200 per oz, and the calculator says so instead of picking a winner. A twin pack of 12 oz jars at $5.28 is $0.220 per oz, 10.0% more; it would match the others at $4.80.

For toilet paper, compare sheets, not rolls, because roll sizes vary. Twelve double rolls of 264 sheets for $13.99 are $0.442 per 100 sheets, 24 regular rolls of 176 sheets for $17.99 are $0.426, and 6 mega rolls of 396 sheets for $9.49 are $0.399, the best value. A pack described only as 18 rolls can’t join that ranking, so it is shown on its own at $0.722 per roll.

Weight ounces vs fluid ounces

An ounce (oz) is a weight and a fluid ounce (fl oz) is a volume, so they can’t be compared without the product’s density. Federal labeling rules declare liquids in fluid measure and solid, semisolid or viscous products by weight, so a thick product such as honey or peanut butter is normally declared by weight (“net wt”). If one package of a product says oz and another says fl oz, check both labels before comparing.

The calculator keeps them apart. With two jars of honey sold by weight and a squeeze bottle labeled 16 fl oz, the jars are ranked (a 32 oz jar at $10.99 is $0.343 per oz; a 12 oz bear at $4.99 is $0.416 per oz, 21.1% more) and the bottle is listed separately at $0.374 per fl oz, with a warning that names both units.

The unit list also has the UK imperial fluid ounce. A US fluid ounce is 29.5735 mL and a UK one 28.4131 mL, so the US ounce is about 4.1% larger. US packages use the US fluid ounce; if you enter both, the calculator converts them before ranking and says so.

Is the bigger package always cheaper?

No, on two counts. First, the largest pack doesn’t always have the lowest unit price: in the worked example, the 12-pack holds the most soda and costs the most per fluid ounce. Second, the lowest unit price is only a saving if you use what you buy.

A cereal aisle shows the second point. A 12 oz regular box costs $3.79 ($0.316 per oz), a 19.3 oz family size $5.29 ($0.274 per oz) and a club 2-pack of 28 oz boxes $12.49 ($0.223 per oz, the best value). If you will eat only 24 oz before it goes stale, two regular boxes cost $7.58 with nothing left over, while the club pack costs $12.49 and leaves 32 oz. Per ounce you actually eat, that is $0.316 against $0.520. Enter the amount under Amount you need and the calculator does this for every item, including the cheapest mix of sizes: for 30 oz, one regular box and one family size (31.3 oz for $9.08) cost less than any single size, the cheapest of which is two family-size boxes at $10.58.

Reading the result

• Best value: the item with the lowest price per unit, or every item that ties for it. Below it are its unit price, how much more the next cheapest costs and, if you entered an amount, the cheapest way to buy it.
• The ranked list runs from cheapest to dearest per unit. Each bar is that item’s unit price as a share of the most expensive one, and each item shows its percentage more than the cheapest.
• Buying … (with an amount you need) lists what each item costs for that amount in whole packs, what is left over and the price per unit of what you use.
• Ranked separately or not ranked holds items measured a different way from the main group, with the reason.
• How this was calculated shows every conversion and division with your numbers.
• The table adds the price paid, the quantity in the comparison unit, the extra per unit and the price to match the cheapest: the highest whole-cent price at which that pack would be at least as good a buy. Download it as a CSV file with Download CSV.

Reading the unit price on a shelf tag

A unit price tag gives the price per unit next to the retail price, and NIST’s guide recommends showing it to the nearest cent at $1 or more and to the nearest cent or tenth of a cent below $1, so 5.2¢ per fl oz is $0.052. Before comparing two tags, check that they use the same unit: per quart on one and per fluid ounce on the other are 32 times apart. A sale or coupon price should have its own unit price; if it doesn’t, enter the deal here. Tags round, so two tags showing the same figure may still differ slightly, and a tag can be wrong; the label’s net quantity and the price you pay are what count.

Assumptions and limitations

• The prices and sizes are the ones you enter; nothing is looked up from a store, and nothing you enter is sent anywhere.
• Unit price measures cost per unit only. It says nothing about quality, how much of a product is usable (bones, packing liquid) or whether a bigger pack will keep.
• Items are ranked only against items measured the same way. Converting a weight to a volume, or rolls to sheets, needs figures that labels don’t give.
• Sales tax, container deposits and delivery fees are left out. A deposit charged per container, where one applies, adds more per ounce to small containers than to large ones.
• The ranking uses exact values. Unit prices are displayed to the cent from $1 and to a tenth of a cent or finer below $1, so two items can show the same rounded price without being tied.
• A percent discount is not rounded to the cent before dividing, as a register might round it.

Common mistakes

• Counting a multipack twice. For 6 × 16.9 fl oz, enter 6 and 16.9, or leave the count blank and enter 101.4; 6 and 101.4 would count six times the soda.
• Treating oz and fl oz as the same unit. One is weight, the other volume; the calculator won’t rank them together, and neither should a shopping list.
• Comparing rolls, loads or “servings” of different sizes. A mega roll is not a regular roll. Compare per sheet, and check how the label defines a load or serving before relying on it.
• Comparing tags in different units. $0.10 per fl oz is $3.20 per quart, not a lower price.
• Assuming the bulk pack wins. Check the unit price, and if you can’t use it all in time, enter the amount you need.
• Forgetting the deal. A “2 for $5” sign or a coupon changes the price you pay; enter it, since the regular tag’s unit price doesn’t include it.