A unit price calculator divides the total price by the package quantity to give you cost per 100 g, per kg, per lb, or per litre. Enter the price and size for two products and it shows which costs less per unit - regardless of whether the labels use different units or sizes.
- Unit price = Total price / Quantity. The lowest number is always the better deal.
- 1 kg = 1,000 g = 2.205 lb = 35.27 oz. The calculator handles all unit conversions automatically.
- Bigger packs are usually cheaper per gram, but not always - premium brands and sale pricing can flip this. Always run the numbers.
- Unit pricing is mandated by law in all 27 EU member states under Directive 98/6/EC (2000) and in 10+ US states.
- Weight (g/kg/oz/lb) and volume (ml/L/fl oz) cannot be compared directly - only compare like for like.
How to use this unit price calculator
Select your currency and choose Metric or Imperial. Then enter the price and package size for each of two items - the units can differ, so one item can be in grams and the other in oz. The calculator shows the unit price in both metric and imperial and highlights the cheaper option with the percentage saving.
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. Under EU Directive 98/6/EC (European Commission, 2000), every retailer in the EU must display the unit price on shelf labels alongside the selling price. This makes cross-brand comparisons fair.
Without unit prices, a 500 g pack at €4.49 and a 750 g pack at €5.99 look similar in cost. With unit prices, you see €0.898 per 100 g vs €0.799 per 100 g instantly. The 750 g pack is 11% cheaper per gram despite the higher total price.
Unit price explained to a beginner
Picture two boxes of pasta at the grocery store. One is 400 g for €2.40. The other is 500 g for €2.75. The bigger box looks more expensive - but is it? 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. That single number - cost per 100 g - is the unit price. It strips away the packaging size and puts every product on the same scale. The same logic works for liquids (price per 100 ml), cleaning products (price per wash), or even toilet paper (price per sheet).
Unit price formula
The formula has one step. Divide the total price by the quantity. All other unit conversions (100 g, per kg, per lb) are just multiplications of this single result.
$$\text{Unit price} = \frac{\text{Total price}}{\text{Quantity}}$$
For weight products, the standard reference unit is 100 g in metric countries and per lb in the US:
$$\text{Price per 100 g} = \frac{\text{Total price}}{\text{Weight in grams}} \times 100$$
For liquids, the reference is 100 ml:
$$\text{Price per 100 ml} = \frac{\text{Total price}}{\text{Volume in ml}} \times 100$$
Worked example - a 500 g bag of coffee for €3.49:
$$\frac{€3.49}{500\,\text{g}} = €0.00698/\text{g} = €0.698/100\,\text{g} = €6.98/\text{kg}$$
Price per 100 g calculation
EU Directive 98/6/EC requires all packaged food sold in the EU to display the price per 100 grams alongside the selling price. It is the standard comparison unit for dry goods, cheese, deli products, and snacks. Divide the price by the weight in grams, then multiply by 100.
Example: a 400 g block of cheddar at €3.80 → €3.80 / 400 × 100 = €0.95 per 100 g.
Price per kg calculation
Used for bulk dry goods - flour, rice, sugar, coffee, and counter-service meat. If you already have the per-100 g price, multiply by 10 to get the price per kilo. One kg = 1,000 g.
Example: a 1.5 kg bag of rice at €2.25 → €2.25 / 1.5 = €1.50 per kg.
Price per lb calculation
Price per pound is the standard weight unit on US grocery labels for meat, deli products, cheese, and produce by weight. Labels typically show a "$X.XX/lb" shelf tag. One lb = 16 oz = 453.6 g.
Example: a 12 oz pack of turkey at $4.49 → 12 oz = 0.75 lb → $4.49 / 0.75 = $5.99 per lb.
See our pounds to ounces converter and ounces to grams converter.
Price per oz calculation
Useful for small packaged goods in the US where weights appear in ounces: spices, nuts, deli meats, and cosmetics. One oz = 28.35 g. For tiny portions like spices, per-oz is often more readable than per-lb.
Example: a 1.5 oz jar of saffron at $6.99 → $6.99 / 1.5 = $4.66 per oz.
See our oz to g converter.
Price per 100 ml calculation
The EU retail standard for liquid products - required on labels for beverages, shampoo, cooking oil, and cleaning products. Divide the price by volume in milliliter, then multiply by 100. Comparable to price per 100 g for dry goods.
Example: a 250 ml bottle of perfume at €42.00 → €42.00 / 250 × 100 = €16.80 per 100 ml.
Price per liter calculation
Standard for cooking oil, large beverage bottles, and cleaning products in metric countries. If you have the per-100 ml price, multiply by 10 to get per liter. One liter = 1,000 ml = 33.81 fl oz.
Example: a 1.5 L bottle of olive oil at €3.60 → €3.60 / 1.5 = €2.40 per liter.
See our liters to fluid ounces converter.
Price per fl oz calculation
The standard volume unit on US liquid product labels: juices, sports drinks, shampoo, and condiments. One US fl oz = 29.57 ml, so a 20 fl oz bottle holds about 591 ml. Use this unit when comparing products labeled in fl oz.
Example: a 20 fl oz sports drink at $2.49 → $2.49 / 20 = $0.12 per fl oz.
See our fluid ounces to milliliters converter.
Price per gallon calculation
Common for fuel at US gas stations, large jugs of water, cleaning supplies, and paint. One US gallon = 128 fl oz = 3.785 liters. For large containers, per-gallon is often the most practical comparison unit.
Example: a 2.5 gallon container of laundry detergent at $22.99 → $22.99 / 2.5 = $9.20 per gallon.
See our US gallons to liters converter.
Price per unit (count) calculation
Used for multi-packs where the individual item count matters more than weight or volume: eggs, vitamin tablets, paper towels, water bottles, or batteries. Divide the total price by the number of items in the pack.
Example: a pack of 48 vitamin tablets at $12.99 → $12.99 / 48 = $0.27 per tablet.
How to compare unit prices for best value
Calculate the same unit (e.g. price per 100 g) for every option, then pick the lowest number. According to a 2023 US Consumer Expenditure Survey (BLS), US households spent an average of $412 per month on groceries.
Consistently buying the lower unit price product across just 10 routine items saves an estimated $400-600 per year.
| Product | Total price | Size | Per 100 g | Best 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 | Best value |
| Coffee D (store brand) | €5.99 | 500 g | €1.198 | Best value overall |
When I work through grocery comparisons like this table, one pattern shows up consistently: the store brand at a midrange pack size often beats the premium brand's largest size on unit price.
The brand premium is real and sometimes visible in ingredient quality, but on a pure price-per-gram basis, it rarely survives the calculation.
Weight and volume unit reference
The most common comparison error is mixing weight and volume units. A fluid ounce of water weighs about 29.6 g, but a fluid ounce of olive oil weighs 27.6 g - they're not interchangeable. Stick to weight-to-weight or volume-to-volume comparisons.
The table below shows the conversion factors used by this calculator.
| Unit | Grams | Ounces | Pounds |
|---|---|---|---|
| 1 g | 1 | 0.0353 | 0.00220 |
| 100 g | 100 | 3.527 | 0.2205 |
| 1 kg | 1,000 | 35.27 | 2.205 |
| 1 oz | 28.35 | 1 | 0.0625 |
| 1 lb | 453.6 | 16 | 1 |
| Unit | Milliliters | Liters | Fluid oz (US) |
|---|---|---|---|
| 1 ml | 1 | 0.001 | 0.0338 |
| 100 ml | 100 | 0.1 | 3.381 |
| 1 L | 1,000 | 1 | 33.81 |
| 1 fl oz (US) | 29.57 | 0.02957 | 1 |
| 1 pint (US) | 473.2 | 0.4732 | 16 |
| 1 gallon (US) | 3,785 | 3.785 | 128 |
Common mistakes when comparing unit prices
Dividing price by quantity in the wrong order
Unit price is always price / quantity, not quantity / price. Dividing the wrong way gives you units per dollar - which sounds plausible but is the inverse. A spoken sanity check catches this: "50 cents per 100 g" makes sense; "2 hundred-grams per dollar" is odd phrasing and signals a division error.
Comparing weight units with volume units
A 500 ml bottle and a 500 g jar are not the same size for most products. Oil, honey, and sauces are denser than water, so the same volume weighs more. Only compare products that use the same unit type - both by weight or both by volume.
Ignoring "per pack" labeling
Some shelf labels show "price per 100 g" but the product itself is sold in pre-portioned sachets. A box of 20 sachets × 5 g each is 100 g total - but you're buying 20 servings, and the per-sachet cost may matter more than the per-gram price. Use the count unit for products where individual servings are what you're buying.
The wrong-direction error (dividing quantity by price) is the one I see most often when helping people set up grocery comparison spreadsheets.
The result always looks plausible - small decimal number, makes sense as a "rate" - but the moment you try to use it to project a total cost, the math breaks down. If your result gives you something in "grams per dollar," you've divided the wrong way.
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 the standard metric for comparing differently sized products on the same basis, and it 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. Example: €4.99 for 750 g = €4.99 / 0.75 kg = €6.65 per kg. This calculator handles the conversion automatically - enter the weight in any unit and it outputs per-kg alongside per-lb.
Is a bigger pack always cheaper per unit?
Usually, but not always. Sales pricing on smaller sizes, premium brand pricing on large formats, and store-brand vs. name-brand comparisons all create exceptions. The only reliable method is to calculate the unit price for every option before buying - never assume size alone determines value.
Can I compare a price per kg with a price per lb?
Not directly - 1 kg = 2.205 lb, so the scales are different. Enter one item in kg and the other in lb in this calculator and it converts both to grams internally, then shows results in matching units. You can also compare the per-kg column for both items.
What is the difference between unit price and unit rate?
Unit price is a specific application - cost per unit of product. Unit rate is the broader mathematical concept: any quantity expressed per one unit, including speed (km per hour), pay ($ per hour), or fuel efficiency (km per litre). 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 formula for unit price?
5. A 2 L bottle of juice costs €3.60. A 330 ml can costs €1.10. Which is cheaper per 100 ml?