Unit Price Comparator

Frequently Asked Questions

• What is a unit price and why does it matter?+
  It is what a product costs per standard amount — per 100 grams, per 100 millilitres, or per item — rather than what it costs per pack. It matters because pack sizes are deliberately not comparable. A 480 g box beside a 500 g box beside a 1.2 kg box cannot be ranked by the price on the shelf edge, and that is not an accident of packaging: it is how the shelf is designed. Reducing everything to one common amount is the only way to see which is actually cheaper, and it frequently is not the one that looks it.
• Why will this tool not compare grams to millilitres?+
  Because it cannot be done honestly without knowing the density of the specific product, and the label does not tell you. Most comparators quietly assume water — 1 gram per millilitre — and print a confident answer. For water that is right. For cooking oil, which is about 0.92, it is off by 8%. For honey, at roughly 1.42, it is off by more than 40%, which is far larger than the price differences you are trying to detect. Rather than produce a number that looks authoritative and is wrong in a way you cannot see, the tool tells you the comparison is not available and shows each item its own unit price instead.
• How do I handle a “2 for $5” offer?+
  Put 5 in the price, the size of a single pack in the size field, and 2 in the packs field. The packs number multiplies the quantity you are getting, not the price you are paying — so two 400 g jars for $9 is $9 buying 800 g, which works out at $1.125 per 100 g. This is the shape most likely to be got wrong by hand in an aisle, and it is the shape ASEAN supermarket labels use constantly: 3 botol RM10, beli 2 percuma 1, and so on.
• Is the biggest pack always the cheapest per unit?+
  No, and assuming so is the single most expensive shopping habit there is. Retailers know that shoppers treat size as a proxy for value, and price accordingly — the family pack is quite often dearer per gram than the medium one, particularly when the medium size is on promotion. Checking takes ten seconds and the answer is genuinely unpredictable, which is precisely why it is worth checking rather than reasoning about.
• What about items sold by count, like eggs or batteries?+
  Use the “item” unit and put the number in the pack in the size field: a tray of 30 eggs at $6.50 is size 30, unit item, price 6.50. The tool reports those per item rather than per 100, because per-100-eggs is not a quantity anyone thinks in. Count is treated as its own unit family, so the tool will not let you compare a dozen eggs against 500 g of something — a count and a weight are not convertible either.
• Why is per 100 g the default rather than per kilogram?+
  Because most supermarket packs are in the hundreds of grams, and per-100 keeps the numbers in a range you can hold in your head while standing in front of the shelf. Per kilogram tends to produce figures that all look similar until you read the third digit. Nothing is lost either way — the ranking is identical, since it is the same number scaled by ten.
• Does this account for quality, or for what I will actually use?+
  No, and it should not be read as if it does. Unit price is one input to a decision, not the decision. The larger pack that is cheaper per gram is a false economy if half of it spoils before you finish it, and the cheapest per-unit option is a poor buy if you do not like it enough to eat it. The tool answers a narrow arithmetic question precisely; the rest of the judgement is yours.
• What about shelf labels that already show a unit price?+
  Use them when they are legible and on the same basis. The problem is that they often are not. Different products in the same aisle get quoted per 100 g, per kilogram and per item, sometimes on the same shelf, and rounding to two decimals can flatten a real difference between two products to the same printed figure. Where the shelf gives you a consistent basis, trust it. Where it does not, this is faster than trying to normalise three different bases in your head.
• Which fluid ounce does this use?+
  The US fluid ounce, 29.5735295625 ml, and the unit is labelled that way so there is no ambiguity. It matters because the imperial fluid ounce is 28.4130625 ml — about 4% smaller — and a 4% error is larger than most of the price gaps this tool exists to find. If you are working from a UK-labelled import, convert to millilitres first rather than assuming the two ounces are close enough.
• How precise are the conversions?+
  Exact. One pound is defined as 453.59237 grams and one ounce as 28.349523125 grams — these are definitions by international agreement, not measurements with error bars, and the tool uses them in full rather than rounding to 454 and 28.35. Rounded factors are usually harmless, but they can flip a genuinely close comparison, which defeats the point of doing the arithmetic at all.
• Do you store what I enter?+
  No. Everything runs in your browser, nothing is transmitted, and nothing is saved between visits. There is no shopping list kept anywhere and no record of what you compared.