How is the unit price calculated?

Each item's quantity is converted to a base unit — grams for weight, millilitres for volume, or a single item for count — then the price is divided by that base quantity. The result is shown per 100 g, per litre or per item for readability.

Can I compare weight against volume?

Only items measured the same way are compared directly, because a gram and a millilitre are not interchangeable. If you mix weight, volume and count, the tool highlights the best value within each group separately and shows a note.

Are my prices sent anywhere?

No. Every conversion and comparison is computed locally in your browser. Your prices and quantities are never uploaded or stored.

Why is the bigger pack not always cheaper per unit?

Retailers often price larger packs at a higher unit cost than mid-size ones, a pattern sometimes called the bulk-buying trap. Calculating the price per 100 g or per litre reveals it: a 1 kg pack can be dearer per unit than a 500 g one.

How do I compare a kilogram pack with a gram pack?

Enter each with its own unit — one in kg, one in g. The calculator converts both to grams internally and shows each as a price per 100 g, so the different pack sizes line up on one scale.

What units does the calculator support?

Weight: grams, kilograms, ounces and pounds. Volume: millilitres, litres, US fluid ounces and US gallons. Count: a simple each / item. Weight is normalised to grams, volume to millilitres, and count to one item.

Can I compare items sold by weight against items sold by count?

Not directly, because a price per gram and a price per item measure different things. The tool groups by measurement type and highlights the best value separately within weight, volume and count.

Unit Price Comparison Calculator

Unit price comparison calculator

When the same product is sold in several pack sizes, the headline price tells you little about value — a 500 g pack at £2.50 and a 1 kg pack at £4.20 can only be compared once both are reduced to a common price per unit. This calculator does that for you: enter the price and quantity of each option, pick the unit, and it shows the true cost per 100 g, per litre or per item, highlighting the cheapest in green.

How it works

Each item is normalised to a base unit before comparison: weight to grams, volume to millilitres, and count to one item. The conversion factors are exact (1 kg = 1000 g, 1 oz = 28.3495 g, 1 lb = 453.592 g, 1 L = 1000 ml, 1 US fl oz = 29.5735 ml, 1 US gallon = 3785.41 ml). The total base quantity is quantity × factor, and the unit price is price ÷ base quantity. For readability the result is scaled to a familiar display unit — per 100 g for weight, per litre for volume, per item for count. Because a gram and a millilitre are not interchangeable, only items measured the same way are ranked against each other.

Example

Compare three options:

Option	Price	Pack size	Price per 100 g
A	£2.50	500 g	£0.50
B	£4.20	1 kg	£0.42
C	£1.80	350 g	£0.51

Option B works out at 4.20 ÷ 1000 g = £0.0042/g, i.e. £0.42 per 100 g — the best value, even though it has the highest sticker price. The smallest pack, C, is actually the dearest per 100 g.

It is privacy-first: all the arithmetic runs in your browser and your prices never leave your device.