Unit Price
Use the Unit Price Calculator → Try the Unit Price Quiz →Unit price is the cost per standard unit of a product - per 100 g, per kg, per lb, or per litre. It is calculated by dividing the total price by the quantity and is the standard metric for comparing differently sized products.
- Unit price = Total price / Quantity. The product with the lowest unit price always costs less per gram, litre, or unit.
- 1 kg = 1,000 g = 2.205 lb = 35.27 oz. All units convert to a common base so any two products can be compared.
- Bigger packs are usually cheaper per unit, but premium pricing and promotional offers can reverse this - always calculate.
- Weight (g, kg, oz, lb) and volume (ml, L, fl oz) cannot be directly compared; only compare like for like.
- EU Directive 98/6/EC (2000) requires unit price on all retail pre-packaged goods in EU member states.
$$\text{Unit price} = \frac{\text{Total price}}{\text{Quantity}}$$
What is Unit Price?
Unit price is the cost per standard unit of a product - typically expressed as price per 100 grams, per kilogram, per pound, or per litre. It is calculated by dividing the total price of a product by its quantity: Unit Price = Total Price / Quantity. This single number strips away differences in package size and puts every product on the same scale.
Unit price is mandated on retail labels in all 27 EU member states under Directive 98/6/EC (2000) and in over 10 US states. Despite this, label accuracy varies and some products deliberately use unusual reference units (e.g. price per 10 g rather than per 100 g) to obscure comparisons. Calculating unit price independently takes seconds and prevents paying a size premium.
Unit Price explained to a beginner
Think of two boxes of pasta at the grocery store. One is 400 g for $2.40 and the other is 500 g for $2.75. The bigger box looks more expensive at a glance. But divide each price by its weight: $2.40 / 400 = $0.006 per gram; $2.75 / 500 = $0.0055 per gram. Multiply by 100 to get the more readable number: $0.60 per 100 g vs. $0.55 per 100 g.
The 500 g box is actually 8% cheaper per gram, even though it costs more overall. That single number - cost per 100 g - is the unit price. It works the same for liquids (price per 100 ml), cleaning products (price per wash), or toilet paper (price per sheet). One division, then compare.
When to use Unit Price
Use unit price whenever comparing two or more products that come in different package sizes or when a shelf label displays an unusual reference unit. It is especially useful for grocery shopping, bulk buying decisions, and evaluating whether a larger size or a different brand is genuinely cheaper.
Worked examples for Unit Price
This table quickly gives you the overview you need to understand Unit Price and its most important comparisons.
| Product | Total price | Size | Per 100 g | Better value? |
|---|---|---|---|---|
| Coffee A | $4.99 | 250 g | $1.996 | |
| Coffee B | $7.49 | 500 g | $1.498 | |
| Coffee C | $12.99 | 1 kg | $1.299 | Yes |
| Store brand | $5.99 | 500 g | $1.198 | Best overall |
Common pitfalls
The most common error is comparing a price per kg with a price per lb without converting first - 1 kg = 2.205 lb, so the numbers are on different scales. The second trap is comparing weight-based unit prices with volume-based ones (e.g. price per 100 g vs. price per 100 ml) for products like olive oil or honey, where density varies significantly.
US households spend an average of $412 per month on groceries (Bureau of Labor Statistics Consumer Expenditure Survey, 2023); consistently choosing the lower unit price product across routine items saves an estimated $400-600 per year.
Frequently asked questions about Unit Price
What is unit price?
Unit price is the cost per standard unit of a product - per 100 g, per kg, per lb, or per litre. Divide total price by package quantity to get it. It is used to compare differently sized products on the same basis and is legally required on retail labels in the EU and many US states.
How do you calculate price per kg?
Divide the total price by the weight in kilograms. If the weight is in grams, divide by 1,000 first to convert. Example: $4.99 for 750 g = $4.99 / 0.75 kg = $6.65 per kg. This is the standard metric unit price used across Europe.
Is a bigger pack always cheaper per unit?
Usually, but not always. Premium brand large sizes can cost more per gram than a store brand small size. Promotional pricing on smaller packs can temporarily make them cheaper. The only reliable method is to calculate unit price for every option before buying.
What is the difference between unit price and unit rate?
Unit price is specifically the cost per unit of product. Unit rate is the broader mathematical concept of any quantity expressed per one unit - speed (km/h), pay ($ per hour), or calorie density (kcal per 100 g). Every unit price is a unit rate, but not all unit rates are prices.
Quiz: how well do you know unit pricing?
1. A 400 g jar of peanut butter costs $3.20. What is the unit price per 100 g?
2. Product A is $4.99 for 750 g. Product B is $3.49 for 500 g. Which is cheaper per 100 g?
3. Why can you not directly compare a price per kg with a price per lb?
4. What is the correct unit price formula?