🛒 Grocery Unit Price Calculator
Work out which pack is genuinely cheaper per unit, not just which one has the smaller price on the shelf. Enter what you can see on the label — the price, the size and the unit — and this page converts everything onto the same basis so the options can be compared directly.
A comparison tool for figures you enter yourself. It does not look up shop prices and it is not financial advice.
Compare pack sizes
Add two to four products. Every option has to use the same kind of unit — all weight, all volume, or all count — because a price per gram and a price per millilitre are not comparable.
Basket against your budget
Optional. Totals you type in yourself — nothing is looked up, and no shop prices are fetched.
Everything you type stays in this browser. No prices, product names or totals are sent anywhere, saved to your device, or put into the page address.
How the unit price is worked out
- Every quantity is converted to one base unit first: grams for weight, millilitres for volume, and items for count.
1 kgbecomes1000 gand2 lbecomes2000 ml. - If you enter a multipack count, the pack size is multiplied by it, so
6 × 330 mlis treated as1980 ml. - The unit price is
price ÷ total base quantity. That figure is then shown per 100 g and per kg for weight, per 100 ml and per litre for volume, or per item for count. - The percentage is measured against the cheapest option:
(this unit price − lowest unit price) ÷ lowest unit price × 100. - The annual estimate, if you fill in how often you buy the product, prices every option for the same amount of product — the cheapest option's pack size — bought that many times a week, for 52 weeks.
Not sure which saving habit to try next?
The calculator above is the part that does the arithmetic. This wheel is optional — spin it if you want one grocery habit to focus on for the week rather than trying to change everything at once.
🛒 Result
A worked example
A shelf shows 500 g of oats for £2.00 next to 1 kg of oats for £3.00. The bigger bag has the bigger price tag, so it looks like the expensive one.
Converted: the 500 g bag is £4.00 per kg (£2.00 ÷ 0.5 kg). The 1 kg bag is £3.00 per kg. The larger bag is £1.00 per kg cheaper — the smaller one costs 33.3% more per kilogram.
Buy oats once a week and, priced for the same 1 kg each time, that gap is about £52 a year. Whether the big bag is right for you is a different question: if half of it goes stale before you finish it, the cheaper unit price stops being the cheaper option.
Frequently asked questions
Why will it not compare 500 g with 1 litre?
Because there is no honest answer. Grams measure weight and litres measure volume, and how they relate depends entirely on what the product is. Rather than invent a conversion, the calculator refuses and explains why, so you never get a confident-looking number that means nothing.
Does it look up real supermarket prices?
No. It has no connection to any shop. Every figure comes from what you type in from the label or your receipt, which is also why nothing you enter has to leave your browser.
Is the lowest unit price always the best buy?
No, and the tool says so under every result. Waste, storage space, expiry dates, quality differences and offers on the smaller pack can all outweigh a lower price per kilogram. The unit price is one input to your decision, not the decision.
How is the annual figure calculated?
It prices every option for the same amount of product — the cheapest option's pack size — bought as often as you said, over 52 weeks. It is clearly labelled an estimate, and it only appears if you fill in the optional frequency field.
What does the multipack field do?
It multiplies the quantity. If you enter 330 ml with 6 packs, the calculator treats the purchase as 1980 ml, so a multipack can be compared fairly against a single large bottle.
Is anything I type saved or sent anywhere?
No. The comparison runs in your browser, nothing is written to storage on this page, nothing is added to the web address, and no prices or product names are included in analytics.
How the wheel works
How does the wheel pick a result?
The wheel selects a result at random before the animation starts, then calculates the exact rotation needed to land that result under the pointer. The displayed result always matches where the wheel visually stops.
Is every option equally likely?
Yes. Every option has an equal chance of being selected, using your browser's built-in random number generator with no weighting or bias.
Can I edit the options?
Yes. Add, remove, or edit any option using the text area on the right. Changes take effect on your next spin and stay only for your current browser session.