Price Per 100G Calculator
Which pack is really cheaper? The Price Per 100g Calculator compares two products side by side: enter each product’s price and weight in grams, kilograms, ounces or pounds, and it returns the cost per 100g and per kg for both, with a plain verdict naming the better deal and how many percent cheaper it is. It is the same unit-price math printed on supermarket shelf tickets, run on the two packs you are actually choosing between, with mixed units handled for you.
Product A
Product B
Per-100g figures compare price only. Quality, freshness and whether you will finish the pack are your call.
Quick Answer
Two bags of oats: Bag A is $4.99 for 350g, Bag B is $6.49 for 500g. Bag A works out to $1.43 per 100g ($14.26/kg); Bag B works out to $1.30 per 100g ($12.98/kg). Bag B costs more at the register but is 9.0% cheaper per 100g, so it is the better buy if you will finish it. These are the calculator's pre-filled values, run them to see the verdict.
Key takeaways
- The bigger pack usually wins per unit, but not always: a sale on the small pack or a shrunken "value" fill can flip the result, which is exactly what the verdict is for.
- Each product gets its own unit dropdown, so a 1 kg bag can be compared directly against a 12 oz block without any mental conversion.
- The "% cheaper" figure is measured against the more expensive pack, so it reads like a real saving, not an inflated one.
- A lower per-100g price is no deal if half the pack spoils. Buy the size you will finish.
How to use the price per 100g calculator
Enter two packs, click Compare prices, and read the verdict. The results stay hidden until you calculate.
- Enter Product A's price and weight: the net weight printed on the pack, in whatever unit it is printed in. The oats example (4.99, 350, grams) is pre-filled.
- Do the same for Product B: 6.49, 500, grams is pre-filled. The two products do not need to share a unit.
- Click Compare prices: the tool converts both weights to grams, computes the cost per 100g and per kg for each, and names the winner with the percentage saved.
- Use Copy my results or Share results: both sit inside the results box and copy the full comparison line, including the verdict.
One habit that pays off: compare the net weight, not the package claims. A "value pack" can hide a smaller fill, and only the grams on the nutrition panel settle it. For perishables, Connecticut's consumer-protection office makes the same point about waste: a lower unit price is no saving if the extra spoils before you use it.
The price per 100g formula
Price per 100g = (total price / weight in grams) x 100. Weights in other units are converted to grams first, using exact conversion factors; price per kilogram is the per-100g figure x 10.
Price per kg = Price per 100g × 10
| Unit entered | Conversion to grams |
|---|---|
| Grams (g) | weight x 1 |
| Kilograms (kg) | weight x 1,000 |
| Ounces (oz) | weight x 28.349523125 |
| Pounds (lb) | weight x 453.59237 |
The ounce and pound factors are the exact international definitions, carried to full precision so mixed-unit comparisons do not pick up rounding drift.
Worked example: two bags of oats, checked against the tool
Bag A is $4.99 for 350g and Bag B is $6.49 for 500g. Those values are pre-filled above, so click Compare prices and check each line:
The same run, plus two more real runs of this calculator, sits in the table below. Every figure is what the tool actually returns, so type any row in and you will get the same numbers back. Note the cheese row: the 12 oz block beats the 1 lb block even though the per-pound shelf ticket can make the pound block look cheaper.
| Comparison | Product A per 100g | Product B per 100g | Verdict |
|---|---|---|---|
| Oats: $4.99/350g vs $6.49/500g | $1.43 ($14.26/kg) | $1.30 ($12.98/kg) | B wins, 9.0% cheaper |
| Beef: $8.00/500g vs $11.00/750g | $1.60 ($16.00/kg) | $1.47 ($14.67/kg) | B wins, 8.3% cheaper |
| Cheese: $3.99/12oz vs $5.49/1lb | $1.17 ($11.73/kg) | $1.21 ($12.10/kg) | A wins, 3.1% cheaper |
Coffee drinkers get the same treatment every morning: a 250g bag at $7.50 is $3.00 per 100g, a 1kg bag at $26 is $2.60 per 100g, and the bulk bag is 13.3% cheaper per 100g. If that coffee budget needs a wider look, the coffee savings calculator tracks what the habit costs over a year.
Why 100 grams is the unit on the ticket
Unit pricing exists because pack sizes lie by omission. In the EU it is law: the Price Indication Directive requires sellers to show the unit price alongside the selling price so shoppers can compare across pack sizes, as summarized in the EU's official price-indication summary.
The US is patchy. Consumer-finance reporting notes that NIST has flagged stores pricing similar items in different units, one juice per gallon, another per quart, a third per fluid ounce, and only a minority of states actually require unit-price tags. Where the tag is missing or the units do not match, the comparison dies at the shelf.
That is the gap this tool closes. It does the conversion the shelf ticket skipped: pick each pack's printed unit in its own dropdown, and the comparison happens in grams before you see a number. For items weighed in milligrams, vitamins, spices, supplements, the sibling price per mg calculator keeps the decimals readable.
What competing calculators miss
Most per-100g tools on the web share one blind spot: they take a single product and report one number. Useful, but the actual shopping question is always "this one or that one," and it usually arrives with two different units on the packs:
- Single-product tools (Calculator Ultra, Brave Calculator's cost pages): one price, one weight, grams only. You run it twice, on paper, and do the subtraction yourself. No side-by-side, no verdict, no mixed units.
- Grocery guide tools (UseCos, iToolVerse): good context on shrinkflation and legal unit-pricing rules, but the calculator is a single-input widget again, and the verdict you actually want, which pack and by how much, never appears.
- Mobile apps (Per100 on iOS/Android): fast in-aisle comparison with history, but an app install and a phone in hand. Nothing you can open on a desktop while planning the shop.
- The gap this page fills: a genuine two-product comparison where each side can be in a different unit, per-100g and per-kg lines for both, exact full-precision conversions, and a verdict stating the saving as a percentage of the more expensive pack. No app, no second run, no paper.
Frequently asked questions
Because 100g lands in readable numbers. Per gram gives tiny decimals like $0.0143/g, and per kilogram gives awkward figures for small items: a 50g jar of spices at $1.40 is $28.00/kg, which looks absurd. Most groceries fall in the $0.50 to $5 per 100g band, which is why supermarkets settled on it for shelf tickets.
Yes. Each product has its own unit dropdown, and the calculator converts both weights to grams before comparing: kilograms x 1,000, ounces x 28.349523125, pounds x 453.59237. The cheese row in the worked examples above compares a 12 oz block against a 1 lb block exactly this way.
It compares the two cost-per-100g figures and names the lower one. The "% cheaper" saving is measured against the more expensive pack: (higher price minus lower price) divided by the higher price, times 100, shown to one decimal. If both packs cost the same per 100g, the calculator says so plainly instead of inventing a winner.
For identical products, yes. The exceptions are quality differences and waste. A store brand at a lower per-100g price is not the same comparison as a premium brand, and the cheapest per unit is no deal if half of it spoils before you eat it. Buy the size you will actually finish.
Yes. It works for anything sold by weight: pet food, coffee, cosmetics, hardware, garden supplies. For items weighed in milligrams, such as vitamins or saffron, the price per mg calculator keeps the decimals readable where per-100g would give tiny fractions.
Because unit-pricing rules are patchy. In the EU, showing the unit price is mandatory; in the US only a minority of states require it, and even where tags exist, similar items can be priced per gallon, per quart and per fluid ounce on the same shelf. When the units do not match, convert before you compare, which is exactly what this tool does for you.
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References
- European Commission. Price indications on consumer products, EUR-Lex summary of Directive 98/6/EC. Accessed October 23, 2026.
- European Parliament and Council. Directive 98/6/EC on consumer protection in the indication of the prices of products offered to consumers, Articles 2-3. Accessed October 23, 2026.
- Bureau International des Poids et Mesures (BIPM). The International System of Units (SI Brochure), defining the gram and kilogram. Accessed October 23, 2026.
- Connecticut Department of Consumer Protection. Saving Money with Unit Pricing. Accessed October 23, 2026.
- Money Crashers. Unit Pricing: The Family Size Is Not Always the Cheaper Buy, reporting NIST findings on mixed-unit shelf tags and state requirements. Accessed October 23, 2026.
- New Zealand Consumer Protection. Saving at the supermarket with unit prices. Accessed October 23, 2026.