Worldwide
Unit price calculator
The cheaper sticker is not always the better buy, and the only reliable way to tell is the unit price, the cost of a single unit of what you are buying.
Unit price is the price divided by the pack size, which puts two differently sized options on the same footing.
This calculator compares two options on that basis: enter the price and pack size of each, and it works out the price per unit for both, names the better value, and shows how much cheaper it is. It settles the everyday supermarket question of whether the big pack really saves money or whether the small one, oddly, costs less per gram. Unit price is a plain division, the price divided by the size, but doing it in your head across two different pack sizes and two different prices is exactly the sort of sum shops rely on you not bothering with. The trick is to make sure both sizes are measured in the same thing. Grams against grams, millilitres against millilitres, sheets against sheets, teabags against teabags, or just plain count against count. As long as the two match, the scale itself does not matter, because both unit prices are worked out the same way and the comparison is fair. This tool shows the unit prices per 100 units to keep the numbers readable, so per 100 grams or per 100 millilitres, but that is only presentation; the winner would be identical if it showed the price per single unit. A worked case makes it concrete. A 500 gram jar at 2.50 works out at 0.50 per 100 grams. A 1,000 gram jar at 4.20 works out at 0.42 per 100 grams. The big jar is cheaper per unit, by 16 percent, so it is the better value despite the higher price on the shelf. Flip the numbers and the answer can flip too: if that larger jar were priced at 5.20, its unit price would rise to 0.52 per 100 grams and the small jar would win, even though it looks like the cheaper, less generous option. This is why "bigger is cheaper" is a rule of thumb, not a law. Manufacturers and retailers price packs to steer choices, and it is common to find the medium size worse value than both the small and the large, or a multipack that costs more per unit than singles once a promotion on the singles is counted. Many countries require shops to display a unit price on the shelf label precisely so shoppers can compare, but the displayed unit is not always the one you would pick, the label can be missing or wrong, and online listings frequently omit it. Working it out yourself removes the doubt. People reach for this when choosing between pack sizes of the same product, when a coupon or multibuy makes a headline price hard to compare, when a own-brand and a premium brand come in different sizes, and when deciding whether to stock up. A few things are worth holding in mind beyond the raw number. Unit price ignores whether you will actually use the larger quantity, so a cheaper unit price on something perishable is a false economy if half of it spoils. It also ignores quality differences, since two products at the same unit price are not the same buy if one is stronger, more concentrated or just better. Concentrated versions need care: a smaller bottle of concentrate can beat a larger ready-to-use one once you account for how far each goes, so compare the made-up quantity rather than the bottle where dilution is involved. And a lower unit price achieved only by buying far more than you need is not a saving if it ties up money or space you would rather keep. The calculator gives you the clean, like-for-like figure so you can start from facts, then layer your own judgement about how much you will use and how the two products actually compare. Enter both prices and both sizes in the same measure, read off which is better and by how much, and you will never again be caught out by a large pack that quietly costs more per unit than the small one beside it.
How it works
- Enter the price of the first option and its size or quantity.
- Enter the price and size of the second option, using the same measure for both.
- The calculator divides each price by its size to get a price per unit.
- It compares the two unit prices and names the cheaper one as the better value.
- The difference is shown as a percentage, how much less the better option costs per unit.
unit price = price / size; better value = the lower unit price
Each option's price is divided by its size to give a cost per unit, both in the same measure so they can be set side by side. The lower unit price is the better value. The percentage difference is the gap between the two unit prices as a share of the dearer one, which is how much less the cheaper option costs for the same amount of product.
- price
- the amount charged for the pack
- size
- the quantity in the pack, in a measure shared by both options
- unit price
- price divided by size, the cost of one unit
When the bigger pack does not win
| 500 g at 2.50 | 0.50 per 100 g | the smaller jar |
| 1,000 g at 4.20 | 0.42 per 100 g | better value, cheaper per unit |
| 1,000 g at 5.20 | 0.52 per 100 g | now the small jar wins |
| Rule of thumb | Check, do not assume | medium sizes are often worst value |
Worked example
A 500 g jar at 2.50 against a 1,000 g jar at 4.20: the small jar is 0.50 per 100 g and the large jar is 0.42 per 100 g, so the large jar is the better value, cheaper by about 16 percent per unit. If the large jar were 5.20 instead, it would be 0.52 per 100 g and the small jar would win.
Key facts
- Unit price is the price divided by the pack size, the cost of a single unit.
- The lower unit price is the better value, whichever sticker looks cheaper.
- Bigger packs are usually but not always cheaper per unit, so it pays to check.
- Both sizes must be in the same measure for the comparison to be fair.
Tips
- Match the units before comparing: grams with grams, millilitres with millilitres.
- Check the shelf unit-price label, but redo it yourself when the label is missing or online.
- For concentrates, compare the made-up quantity rather than the bottle size.
- A lower unit price only saves money if you actually use the larger quantity.
Frequently asked questions
What units should I use for the size?+
Whatever the two options share, as long as both use the same one. Grams against grams, millilitres against millilitres, or plain count against count all work. The actual scale does not affect which is cheaper, because both unit prices are worked out the same way, so you do not need to convert to any particular unit, only to match them.
Is the bigger pack always cheaper per unit?+
No. It usually is, but not always. Retailers sometimes price a small or medium pack lower per unit to clear stock or to make a multibuy look better, and promotions on the smaller size can beat the large one. That is exactly why it is worth checking rather than assuming, and why this tool exists.
Why is the unit price shown per 100 units?+
Only to keep the numbers readable, since a price per single gram or millilitre is often a tiny fraction. Showing it per 100 grams or per 100 millilitres gives a figure you can actually compare at a glance. The winner and the percentage difference are the same whatever scale is used to display it.
Does a lower unit price always mean I should buy it?+
Not on its own. A cheaper unit price is a real saving only if you use the quantity. For something perishable, buying more than you will get through can waste more than it saves. Unit price also ignores quality and concentration, so weigh those alongside the number rather than treating the lowest unit price as the automatic winner.
How do I compare a concentrate with a ready-to-use product?+
Compare the made-up quantity, not the bottle. A concentrate goes further, so work out how much usable product each option yields after dilution, then compare the price against that. Entering the raw bottle sizes would understate the concentrate, since a small bottle of it can replace a much larger ready-to-use one.
Things to watch
- A cheaper unit price on a perishable is a false economy if part of it spoils unused.
- Unit price ignores quality and strength, so equal unit prices are not always equal buys.
- Buying far more than you need to reach a lower unit price ties up money and space.
Last updated: 2026
This is an estimate for general guidance, not financial, tax, legal or medical advice. Figures can change and individual circumstances vary. Always confirm with an official source before making decisions.
Built and maintained by Vikas Dulgunde. Editorial standards.