Unit Price Calculator
Use this price per unit comparison calculator to compare up to eight pack sizes and find the cheapest option. It works with grams, kilograms, ounces, pounds, millilitres, litres, fluid ounces, US gallons, items and dozens, and shows each price per 100 g, per 100 ml or per item.
Quick answer: To compare pack sizes, divide each price by its size to get a price per 100 g, 100 ml or item, then pick the lowest. A 500 g pack at £2.50 costs £0.50 per 100 g, while a 300 g pack at £1.80 costs £0.60, so the larger pack is cheaper. The calculator converts units for you.
How do you use the Unit Price Calculator?
- Add each product. Enter the price, the size, the unit and the number of packs for every option.
- Press Compare Prices. The calculator converts everything to one unit, such as per 100 g or per 100 ml.
- Read the cheapest option. The best unit price is highlighted, with how much more each other pack costs.
What is the formula, and what does a worked example look like?
Formula: Unit price = price ÷ (size × units per pack × number of packs), converted to a standard unit.
Example: 500 g for 3.00 = 0.60 per 100 g. 1 kg for 5.00 = 0.50 per 100 g, so the larger pack is 20% cheaper.
Method & source: Unit conversion to grams, millilitres or items; SI and US customary factors. See how we test our calculators.
Next step: try percentage change or reverse percentage.
How do you compare prices per unit?
A unit price calculator converts the price of any pack into the cost of a single standard unit, such as per 100 grams, per 100 millilitres or per item. Once every option is priced in the same unit, the best deal is obvious.
This price per unit comparison calculator understands different sizes and measurement systems, so you can compare a 750 g box, a 1.5 kg bag and a 2 lb pack in one go.
How do you compare different pack sizes?
Add each product you want to compare with its price, size, unit and number of packs.
- Unit conversion: Grams, kilograms, ounces and pounds; millilitres, litres, fluid ounces and gallons; items and dozens.
- Standard price: Weight and volume are shown per 100 g or 100 ml, counts per item.
- Best value: The cheapest option is highlighted automatically.
- How much more: Every other option shows the percentage extra you would pay.
- Multipacks: Enter the number of packs to compare bundles fairly.
Only like-for-like units can be compared, so the calculator will tell you if you mix weight with volume or count.
Why does comparing unit prices matter?
Bigger is not always cheaper. Packaging, promotions and odd sizes make the sticker price a poor guide to value.
- Spot the genuinely cheapest size on the shelf.
- Compare brands sold in different units.
- Check whether a bulk buy really saves money.
- Keep a grocery budget under control.
- Judge promotions such as “3 for 2” objectively.
A quick comparison of price per unit takes seconds and can save a meaningful amount over a year of shopping.
Worked walkthrough: cereal boxes
A 750 g box of cereal costs 3.15 and a 1.2 kg box costs 4.68. Converting both to the same unit gives 0.42 per 100 g for the small box and 0.39 per 100 g for the large one. The larger box is cheaper, and the smaller one costs about 7.7% more per gram. If you add a third option, such as a two-pack of 500 g boxes for 5.50 (0.55 per 100 g), the table ranks all three and marks the best value. Mixed units work too, because pounds, ounces and kilograms are converted to a common base.
Practical tips for Unit Price calculations
- Only compare like with like: weight with weight, volume with volume, and counts with counts. The tool warns you if you mix them.
- For multipacks, enter the size of one item and the number of packs, for example 330 ml with 6 packs.
- The cheapest unit price is not always the best deal – consider whether you will use everything before it spoils.
- Check promotions: a “3 for 2” offer changes the price you should enter for that pack.
- Shelf labels sometimes use different units for similar products. Enter the pack details yourself to compare fairly.
How unit price is calculated
Unit price is the price divided by the total quantity you receive, scaled to a standard unit. The calculator converts every size to grams, millilitres or single items, then shows the price per 100 g, per 100 ml or per item. A 500 g box at 3.00 costs 0.60 per 100 g, a 750 g box at 4.20 costs 0.56, and a 1 kg box at 5.20 costs 0.52, so the largest box is about 13% cheaper per 100 g than the smallest.
Weight, volume and count are separate scales
Only compare like with like. Weight (g, kg, oz, lb), volume (ml, l, fl oz) and item counts cannot be converted into each other, because a litre of oil and a kilogram of flour weigh different amounts per litre. If you try to mix kinds, the calculator says so instead of giving a misleading answer. For food sold by weight and by count, look for the net weight on the pack.
Multipacks
For a multipack, enter the size of one item and the number of packs. A six-pack of 330 ml drinks at 2.40 is 1,980 ml in total, or 0.12 per 100 ml. A 2-litre bottle at 1.60 is 0.08 per 100 ml, which is a third cheaper. You can compare up to eight options at once.
Spotting shrinkflation
If a pack shrinks from 500 g to 450 g while the price stays the same, the unit price rises by about 11%. Comparing before and after prices with the percentage change calculator puts a figure on it. Shelf labels help, but many shops show unit prices per kilogram on some products and per 100 g on others, so recalculate on a common base.
When the cheapest unit price is not the best buy
A lower unit price only saves money if you use everything. A family-size pack that spoils, a bulk item you will not finish, or a large bottle that does not fit your storage can cost more than a smaller one. Promotions also change the maths, so model a multi-buy offer as a discount with the discount calculator before you compare.
Worked comparisons: when the bigger pack is not the cheaper one
The calculator converts every pack to a price per 100 g, per 100 ml or per item, so different sizes and units can be compared directly. Four real-style comparisons show what to look for.
| Pack | Unit price | Result |
|---|---|---|
| 500 g for £2.50 | £0.50 per 100 g | 19.0% dearer |
| 300 g for £1.80 | £0.60 per 100 g | 42.9% dearer |
| 1 kg for £4.20 | £0.42 per 100 g | Cheapest |
Percentages are measured against the cheapest pack. The 1 kg pack is cheapest at 42p per 100 g; the 500 g pack is 50p and the 300 g pack is 60p, so the 300 g pack costs 20% more per gram than the 500 g pack.
| Pack | Unit price | Result |
|---|---|---|
| 6 × 330 ml for £3.60 | £0.18 per 100 ml | 29.9% dearer |
| 1.5 L for £2.10 | £0.14 per 100 ml | Cheapest |
| 4 × 500 ml for £4.00 | £0.20 per 100 ml | 42.9% dearer |
Multipacks are not always cheaper: the single 1.5 L bottle works out cheaper than either multipack. Enter the number of packs for multipacks so the calculator multiplies the size for you.
| Pack | Unit price | Result |
|---|---|---|
| 400 g for £2.00 | £0.50 per 100 g | Cheapest |
| 1 kg for £5.50 | £0.55 per 100 g | 10.0% dearer |
The bigger 1 kg pack costs 10% more per 100 g than the 400 g pack, so bulk buying only helps when the unit price is lower. Mixed units are handled too:
| Pack | Unit price | Result |
|---|---|---|
| 16 oz for £3.20 | £0.71 per 100 g | Cheapest |
| 500 g for £3.60 | £0.72 per 100 g | 2.1% dearer |
Frequently Asked Questions (FAQs)
Enter each pack’s price and size, choose the unit and press Calculate. The calculator shows the price per 100 g, 100 ml or item so every pack is on the same scale.
Yes. Weights are converted to a common base, so a 1 kg bag and a 2 lb bag can be compared directly. The same works for litres, millilitres, fluid ounces and gallons.
You cannot compare weight with volume or with item counts. Use the same kind of unit for every product.
Enter the size of a single unit and the number of packs. A 6-pack of 330 ml cans is size 330 ml, packs 6.
Weight and volume are shown per 100 g or 100 ml. Counts are shown per item. The best option is marked and others show how much more you would pay.
Divide the price by the weight in grams and multiply by 100 to get the price per 100 g, which is what the calculator shows; multiply that by 10 for the price per kg. For example, a 500 g pack at 3.20 is 0.64 per 100 g (6.40 per kg) and a 1.2 kg pack at 7.20 is 0.60 per 100 g (6.00 per kg), so the 500 g pack costs 6.7% more. It works with any currency.
Not always. Bigger packs are often cheaper per unit, but promotions and multipacks can change that, so compare the unit prices.
Yes. Press Add option to compare up to eight packs at once, for example several brands and sizes of the same product. Each one gets its own price per 100 g, 100 ml or item, the cheapest is marked as the best value, and the others show how much more you would pay.
Divide each price by its size to get a price per 100 g, 100 ml or item, then compare the results. For 500 g at £2.50 and 300 g at £1.80, that is 50p against 60p per 100 g, so the larger pack is cheaper.
No. A 1 kg pack at £5.50 costs 55p per 100 g, which is more than 400 g at £2.00 (50p per 100 g). Always compare unit prices rather than assuming bulk is cheaper.