About the Price Per Unit Calculator
Which is cheaper: 400 grams for 2.50, 750 grams for 4.20, or 1.5 kilograms for 7.80? Pack sizes are chosen by manufacturers and shops, not by shoppers, and they rarely make comparison easy. Some shelves quote price per 100 g, others per kg or per item, and imported products may be sold in ounces and pounds.
This price per unit calculator compares up to three items by their price per unit of weight, volume or count. It converts between metric and US units — grams, kilograms, ounces and pounds; millilitres, litres, US fluid ounces and gallons — so the comparison is fair, then shows each item's price per kg, per 100 g and per lb (or per litre, 100 ml and fl oz), names the cheapest, and says how much more the most expensive option costs.
How to Use the Price Per Unit Calculator
For each item, enter the price, the size and the unit the size is given in.
You can enter two or three items. Leave the price and size of an unused item blank.
All items must be measured the same way: all by weight, all by volume, or all by count. The calculator cannot compare grams with millilitres, because that would depend on the density of the product.
How Price Per Unit Is Calculated
size in base units = size × conversion factor (to grams, ml or items)
price per unit = price ÷ size in base units
quoted per kg = price per gram × 1,000
difference = (dearest ÷ cheapest − 1) × 100%Conversion factors: 1 oz = 28.35 g, 1 lb = 453.6 g, 1 US fl oz = 29.57 ml, 1 US gallon = 3,785 ml.
Step-by-Step Example
Item A: 2.50 for 400 g. Item B: 4.20 for 750 g. Item C: 7.80 for 1.5 kg.
Item A: 2.50 ÷ 0.40 kg = 6.25 per kg
Item B: 4.20 ÷ 0.75 kg = 5.60 per kg
Item C: 7.80 ÷ 1.50 kg = 5.20 per kg
Difference: 6.25 ÷ 5.20 − 1 = 20.19% more for A than CItem C is the best value. Buying item A instead costs about a fifth more for the same amount of product.
Reading Shelf Labels
Many countries require shops to show a unit price on the shelf label, but the unit is not always the same. One product may be priced per 100 g and a similar one per kg, or one per item and another per 100 g. Multi-buy offers ("3 for 5") often show the single-item unit price rather than the offer price.
Converting everything to one unit, as this calculator does, cuts through that.
When the Cheapest per Unit Is Not the Best Buy
Perishable food. A large pack is only cheaper if you eat it before it goes off. Throwing a third away wipes out a 20% saving.
Storage and cash. Bulk buys tie up money and space. For a household on a tight budget, the smaller pack can be the better choice this week.
Quality differences. Different brands, grades or concentrations are not directly comparable. A concentrated cleaner or a denser product may be better value than its unit price suggests.
Offers on small packs. Temporary discounts can make a smaller pack the cheapest per unit. It is always worth checking rather than assuming.
Using Unit Prices in Business
The same method helps when buying supplies. Suppliers quote different pack sizes, cases and units, and comparing on price per unit — per kilogram, per litre, per item — shows the real cost. For regular purchases, small differences per unit add up quickly over a year.
Price Per Unit and Shrinkflation
Manufacturers sometimes reduce the size of a product while keeping the price and packaging almost the same, a practice often called shrinkflation. A chocolate bar that drops from 200 g to 180 g at the same price is an 11% price rise per gram, even though the shelf price has not changed.
The unit price reveals this immediately. Comparing the price per kilogram or per litre with what you paid before shows the real change, and comparing it with other brands shows whether it is still good value. Keeping a note of the unit price of things you buy regularly makes these changes easy to spot.
Comparing Multi-Buy Offers
Offers such as "3 for 5" or "buy one get one half price" change the unit price only if you buy the full offer quantity. To compare them, work out the total price and total size of the offer and enter those as one item. For example, three 250 g packs for 5.00 is 5.00 for 750 g, which you can compare directly with a single 1 kg pack. Remember that the offer only saves money if you would use all three packs.
Understanding Your Result
Best value names the item with the lowest price per unit.
Item A, B and C show each item's price in three common units.
Difference is how much more the dearest item costs per unit than the cheapest.
Worth knowing reminds you that the cheapest per unit only saves money if you use it all.
When Should You Use This Calculator?
Grocery shopping, to compare pack sizes and brands.
Comparing multi-buy offers with single packs.
Buying household and cleaning products.
Choosing between suppliers of business consumables.
Comparing imported products sold in ounces with local ones sold in grams.
Common Mistakes
Assuming the biggest pack is cheapest.
Comparing different units, such as per 100 g on one label and per kg on another.
Comparing weight with volume for liquids and powders.
Ignoring waste from food that spoils before it is used.
Forgetting quality differences between products.