Free Unit Price Comparison calculator
Enter the price and size of two or three products — different units and multipacks are fine — and see the cost per unit for each, which one is the best value, and how much you save, updated live, as you type.
On this page15 sections
Option B gives you 40 oz of product for the lowest cost per oz.
Estimates only, based on the prices and sizes you enter. Confirm before you buy.
Results are estimates. Consult a professional.
How the unit price calculator works
A unit price is the cost of one standard unit of a product — one ounce, one litre, one item — instead of the price on the shelf. The calculator takes each product's total price and its total quantity, divides one by the other, and lines the results up side by side. The lowest number is the best value, and that is the only comparison that holds when packages come in different sizes.
What the result tells you
Two numbers do the work. The unit price for each item is what you compare; the percentage saving is what you pocket by picking the cheapest one. The calculator flags the winner and shows how much more every other option costs per unit, so a 7% gap that hides behind a tempting "value size" sticker becomes obvious before it reaches your cart.
What goes into a fair unit price comparison
A unit price comparison is built from four inputs per product. Get each one right and the ranking is right; mix up the units and the cheapest option can look like the most expensive.
Total price — what you pay at the register
The full shelf price of the package, before any per-unit math. This is the number the store advertises in big type, and it is the one that makes a bigger box feel like a bargain. On its own it tells you nothing about value.
Quantity and unit — how much you get
The size of the package, with its unit attached: 28 ounces, 2 litres, 12 rolls. The unit is the part shoppers skip, and it is the part that matters most. Comparing $4.49 to $5.99 is meaningless until both are expressed per ounce or per litre.
Pack count — for multipacks and cases
When a product is sold as several items in one package — a six-pack of cans, a case of 24 water bottles, a twin-pack of detergent — the total quantity is the pack count times the size of one item. Six 12-ounce cans is 72 ounces, not 12. The calculator multiplies this out so a case and a single bottle land on the same scale.
A worked example: comparing two jars by price per ounce
Maria is buying peanut butter. The small jar is 28 oz for $4.49; the big jar is 40 oz for $5.99. The big jar costs more, but is it the better value? She compares them by price per ounce.
Step 1 — Find each unit price
Small jar: 4.49 ÷ 28 = $0.1604 per oz. Big jar: 5.99 ÷ 40 = $0.1498 per oz.
Step 2 — Pick the lowest
$0.1498 is less than $0.1604, so the 40 oz jar wins. Here the bigger package is the cheaper one per ounce. Only the per-ounce math proves it.
Step 3 — Measure the saving
The small jar costs (0.1604 − 0.1498) ÷ 0.1498 = 7.1% more per ounce. Put the other way, choosing the big jar saves about 6.6% on every ounce of peanut butter.
How to compare different units and pack sizes
The hard comparisons are the ones where nothing matches: a bag priced per pound next to a box priced per ounce, or a six-pack of cans next to a single large bottle. The fix is always the same — convert everything to one unit first, counting multipacks in full.
Different units — convert to a common one
Pick one unit and move both products to it. A $6.38, 2-pound bag is $3.19 per pound, which is 3.19 ÷ 16 = $0.199 per oz — now it compares cleanly to anything sold by the ounce. The cubic feet calculator uses the same convert-first logic for volume.
Different pack sizes — count the whole pack
For a multipack, multiply before you divide. A six-pack of 12-ounce cans is 72 ounces total; at $5.49 that is 5.49 ÷ 72 = $0.076 per oz. Compare that against a large bottle's price per ounce, not against a single can.
Why the bigger package isn't always cheaper
Most shoppers assume the bigger size is the better deal. It often is — but not always, and brands count on the assumption. When a "value size" or "bulk" pack carries a higher price per unit than the regular size, that is a quantity surcharge, and it is common enough that consumer advocates treat it as a routine trick rather than a rare slip.
Consumer advocates and researchers have documented this for decades. Store surveys of multi-size brands have found roughly a quarter to a third charge a quantity surcharge on at least one product — the larger size costing more per unit than the smaller one. The only defence is to read the unit price, not the package size.
Grocery-shelf surveys have measured quantity surcharges on about 25–34% of multi-size brands (Journal of Consumer Affairs). University extension programs and USDA's MyPlate both teach unit pricing as the fix — compare cost per ounce or per pound, not the package price.| Two sizes of the same product | Total price | Unit price | Cheaper per unit? |
|---|---|---|---|
| 14 oz box of cereal | $2.52 | $0.180/oz | No |
| 20 oz box of cereal | $3.00 | $0.150/oz | Yes — bigger wins |
| 16 oz block cheese | $4.00 | $0.250/oz | Yes |
| 8 oz shredded cheese | $2.56 | $0.320/oz | No — convenience premium |
Cereal figures follow a university extension shelf-tag example; the cheese figures show how pre-shredded "convenience" packs carry a higher unit price than the block you shred yourself.
The lesson is not "buy big" or "buy small." It is "buy by the unit price," because the cheaper option flips from one product to the next and only the per-unit number tells you which way it went.
Unit price conversions at a glance
Before you can compare, you often have to convert. These are the conversions that come up most in a grocery aisle — use them to move two products onto the same unit.
| To convert | Do this | Example |
|---|---|---|
| Price per lb → price per oz | divide by 16 | $3.19/lb → $0.199/oz |
| Price per oz → price per lb | multiply by 16 | $0.20/oz → $3.20/lb |
| Price per gallon → per fl oz | divide by 128 | $12.80/gal → $0.10/fl oz |
| Price per litre → per 100 ml | divide by 10 | $1.50/L → $0.15/100 ml |
| Multipack → per item | divide by pack count | $6 for 12 → $0.50 each |
| Per item → per ounce | divide by size per item | $0.50 / 8 oz → $0.0625/oz |
One pound is 16 ounces; one US gallon is 128 fluid ounces; one litre is 1,000 millilitres. Convert both products the same way before comparing.
Where unit pricing saves the most money
Reach for a unit price comparison any time two options give you different amounts for different prices — which is most of the grocery store and a fair bit of everywhere else.
- Household staples — paper towels, toilet paper, laundry detergent and trash bags, where pack and roll counts vary wildly between brands.
- Pantry goods — cooking oil, coffee, nuts, rice and spices, often sold in three or four sizes at once.
- Drinks — cans vs bottles vs multipacks, the classic "count the whole pack" comparison.
- Personal care — shampoo, toothpaste and razors, where "value" sizes frequently hide a quantity surcharge.
- Generic vs name brand — to see whether the store brand's lower shelf price survives once both are measured per unit.
It is the same habit of measuring before you buy that drives the square footage calculator — know the true quantity first, then judge the price.
How to read a shelf unit-price tag
Many stores already print the unit price for you, in small type on the shelf tag below the product. Reading it well takes two checks.
Find the small number, not the big one
The large price is what you pay; the smaller "unit price" — often boxed or in the corner — is the cost per ounce, per pound or per 100 sheets. That small number is the one to compare between brands and sizes.
Confirm the units line up
The catch: stores sometimes label one product per ounce and the next per pound, or one per sheet and another per roll, so the printed unit prices are not directly comparable. When the units differ — or when the tag is missing, wrong or smudged — fall back to this calculator and put both on the same unit yourself.
Unit price definitions
How accurate is this unit price calculator?
The math is exact. Total price divided by total quantity is the precise unit price, and the multipack step — pack count times size per item — is plain multiplication. If your price and quantity are right, the unit price and the ranking are right to the cent.
The judgement is yours. The calculator tells you which option is cheapest per unit, but value is more than unit price: a slightly pricier pack you will finish beats a "cheaper" bulk one that spoils, and a unit price that ignores shipping, a coupon or a loyalty discount is only half the picture. Enter each product in the same unit, count multipacks in full, and use the result as the strongest single signal of value — not the only one.
Frequently asked questions about the free Unit Price Comparison calculator
About this Unit Price Comparison calculator
This unit price comparison calculator runs entirely in your browser. Nothing you type is sent anywhere — the price, size, and pack count for each product stay on your device, and the cost-per-unit ranking updates instantly as you change them.
It's part of our home & garden calculators, alongside the rest of the free calculators on the site. Use it in the aisle to compare sizes and brands, or before a bulk order to check that the "value" pack really is the better value.