Unit Price Converter
Normalise two pack sizes to the same unit and see which is genuinely cheaper. Converts price per pack into price per kg, litre or 100 g the way EU shelf labelling requires.
Unit Price Converter
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Mass cannot be compared with volume without a product-specific density, and the page declines rather than assume one.
- Currency is not converted; enter both prices in the same currency.
- Promotional structures such as multi-buys must be reduced to an effective price before entry.
In short: Divide the pack price by the pack quantity to get the unit price, then express both packs in the same unit. Directive 98/6/EC requires that unit price on the shelf edge precisely because the larger pack is not always the cheaper one — and it often is not.
Formula
unit price = pack price ÷ pack quantity
premium % = (dearer ÷ cheaper − 1) × 100
[('pack price', 'the price actually paid, inclusive of tax'), ('pack quantity', 'net quantity converted to kilograms or litres'), ('unit price', 'the comparable figure the shelf edge must show'), ('premium %', 'how much more the dearer pack costs per unit')]
Worked Example
- Convert both pack quantities into the same base unit — kilograms for weight, litres for volume.
- Divide each pack price by its converted quantity.
- Compare the two unit prices directly; the lower one is the better value regardless of pack size.
- Express the result per 100 g or 100 mL if that is the scale on the shelf label.
- Check the break-even price to see what the dearer pack would have to cost to compete.
A 750 g pack at 2.49 works out at 3.32 per kg. The 1.25 kg pack at 4.29 looks like the bulk saving but comes to 3.432 per kg — about 3.3735% dearer. The larger pack would have to be priced at 4.15 to match. This is not a contrived example; it is the ordinary pattern that made unit pricing a legal requirement.
Strengths & Limits Of This Model
Where this engine is strong
- Refuses mass-versus-volume comparisons instead of guessing
- Shows the break-even price, not just which pack wins
- Reports the premium as a percentage of the cheaper unit rate
Where it stops
- No currency conversion
- Does not model promotions directly
Practical Use Cases
Comparing two pack sizes
Settling whether the family size is genuinely cheaper per kilogram.
Checking a multi-buy
Working out the effective unit price once a three-for-two is applied.
Comparing across units
Putting a pack sold in ounces beside one sold in grams on the same basis.
Procurement review
Normalising supplier quotes that arrive in different pack configurations.
Auditing a shelf label
Verifying that the unit price displayed matches the selling price and net quantity.
Methodology & Editorial Standards
Both packs are converted to a single base unit — the kilogram for mass and the litre for volume — using exact definitional factors, then divided into their prices. Mass and volume are treated as separate families and a cross-family comparison is refused rather than resolved with an assumed density, because density is product-specific. The break-even figure is the price at which the dearer pack would match the cheaper pack's unit rate, computed from the quantities entered.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Unit Price Converter — 10 Expert FAQs
10 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Is the bigger pack always cheaper?
No, and assuming so is expensive. Larger packs are frequently priced above the small-pack unit rate because shoppers expect bulk to mean value and do not check. That behaviour is exactly why EU law obliges retailers to print a unit price on the shelf edge.
What is a unit price legally?
Under Directive 98/6/EC it is the final price including VAT and all other taxes for one kilogram, litre, metre, square metre or cubic metre — or for a different single unit that is customary for that product in that member state. It must be unambiguous, easily identifiable and clearly legible.
Per kilogram or per 100 g?
Both appear on shelves. The directive names the kilogram, but allows a customary unit where that is clearer, which is how per 100 g became normal for small packs. Germany moved to require per kilogram for most goods in 2021. The figures are the same number a factor of ten apart.
Why can't I compare grams with millilitres?
Because they measure different physical quantities. One millilitre of honey and one millilitre of oil have different masses, so converting between them needs a density that is specific to the product. This page refuses the comparison rather than invent a density.
How do I handle a three-for-two offer?
Work out what you actually pay for what you actually take home: three items for the price of two at 1.20 each is 2.40 for three, so 0.80 each. Then compare that against the alternative. The shelf unit price usually reflects the undiscounted price, so promotions have to be recalculated by hand.
What is drained weight and why does it matter?
For products packed in liquid, the drained weight is what you actually eat. The directive allows the unit price to be based on it, and where it is, the figure is higher than the gross weight would suggest. A 400 g tin with 240 g drained at 1.09 is 4.54 per drained kilogram, not 2.73.
Does the unit price include tax?
Yes. The directive defines both the selling price and the unit price as final prices including VAT and all other taxes, so the figure on the shelf is directly comparable to what you pay.
Is this the same as a cost-per-serving calculator?
No. This page normalises price against a physical quantity so two packs can be compared. Cost per serving depends on portion size and recipe, and budgeting tools of that kind live in the Everyday Life category.
Do these rules apply outside the EU?
The directive itself applies in the EU, and the UK retained equivalent rules. Australia, parts of Canada and several US states have their own unit-pricing requirements with different detail. The arithmetic is universal even where the labelling obligation is not.
Why is my unit price different from the shelf label?
Common causes are a promotional price the label has not caught up with, a label based on drained rather than gross weight, or a different customary unit — per item rather than per kilogram, for instance. If none of those explain it, the label may simply be wrong, which is a reportable matter.