Unit Price Calculator
Compare the unit price of two products to find the best value. Calculates price per 100g or per unit.
How to use this tool
- Enter price a, weight a, price b and weight b in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your cheaper option saves and the full breakdown beneath it.
Compare two products to instantly find the better value per 100g.
⚠ This tool provides general estimates for education only and is not financial, tax or legal advice. Figures may not reflect your situation — verify with a qualified professional.
Formula
Unit price ($/100g) = price ($) ÷ weight (g) × 100
Saving (%) = (dearer unit price − cheaper unit price) ÷ dearer unit price × 100
unit_a = price_a / weight_a × 100saving_pct = (max − min) / max × 100
How it works
This calculator normalises the price of two products to a common basis ($/100g) so they can be compared regardless of pack size. It then calculates how much cheaper the better-value product is as a percentage of the dearer option's unit price.
The comparison assumes both products are measured in grams and the same currency. If the two unit prices are equal, the saving is 0% — as in the golden case where both products happen to cost $0.70 per 100g despite different pack sizes and prices.
Worked example
- Product A: $3.50 for 500 g. Product B: $2.80 for 400 g.
- Unit price A = $3.50 ÷ 500 × 100 = $0.70/100g.
- Unit price B = $2.80 ÷ 400 × 100 = $0.70/100g.
- Both prices are equal, so saving = (0.70 − 0.70) ÷ 0.70 × 100 = 0.0%.
Price A per 100g = $0.70; Price B per 100g = $0.70; Cheaper option saves 0.0%
Common mistakes to avoid
- Comparing price per 100 g for a perishable product when one size has a shorter shelf life — the cheaper unit price is irrelevant if the larger pack goes to waste.
- Ignoring pack format differences: loose items priced per kg vs. pre-packaged items priced per unit may include different packaging weight.
- Failing to check for loyalty-card or multi-buy pricing that changes the effective unit cost at the register.
Key terms
- Unit price
- The cost per standard quantity (here per 100g), enabling fair comparison between products sold in different pack sizes.
- Price per 100g
- A common supermarket comparison metric; legally required to be displayed on shelf labels in many countries.
- Saving percentage
- How much less the cheaper product costs relative to the dearer one, expressed as a percentage of the dearer unit price.
- Pack size
- The total weight of contents in a product package; larger packs are often — but not always — better value per unit weight.
Frequently asked questions
- How do I compare unit prices?
- Divide each product's price by its weight in grams, then multiply by 100 to get the cost per 100g. The lower figure is better value.