Unit Price Calculation
Unit price lets you compare different pack sizes by reducing everything to the same base unit. Larger packs are usually cheaper per unit — but not always.
Formula
Unit price = Total price / Quantity
(in consistent units)
Examples:
500g cereal for £2.80 → £2.80/500 = £0.56/100g
1kg cereal for £4.60 → £4.60/1000 = £0.46/100g
Larger pack wins: £0.46 vs £0.56 per 100gCommon Comparisons
6-pack water (6×500mL) £3.60 vs 2L bottle £1.20:
6-pack: £3.60/3000mL = £0.12/100mL
2L: £1.20/2000mL = £0.06/100mL
→ 2L bottle is 2× better valueWhen Bigger Isn't Better
- Perishables you'll waste before using = false economy
- Storage cost and space
- Cash flow: tied up capital vs. cheaper per unit
- Sale items: sometimes smaller packs go on sale at better unit price
Compare unit prices: Free Unit Price Calculator
Unit Price Quick-Reference Examples
| Product A | Price A | Product B | Price B | Better value |
|---|---|---|---|---|
| 500 mL bottle | $1.50 | 1.5 L bottle | $3.80 | B ($2.53/L vs. $3.00/L) |
| 12 eggs | $3.49 | 18 eggs | $4.99 | B ($0.277 vs $0.291 each) |
| 200 g cereal | $2.99 | 500 g cereal | $6.49 | A ($14.95/kg vs. $12.98/kg) |
| 4-pack 500 mL | $5.60 | 8-pack 330 mL | $7.20 | Compare: $2.80/L vs. $2.73/L → B |
How Unit Price Calculations Work
Unit price = total price ÷ quantity. Compare products by expressing price in the same unit: per litre, per gram, per kilogram, per 100 ml, per sheet, or per unit. In the EU and many countries, retailers are legally required to display the unit price alongside the shelf price. In the US, shelf tags typically show unit price but display formats vary by retailer.
Unit price exposes "shrinkflation" — when manufacturers reduce product size while keeping the price the same (or raising it slightly). A product that "appears" the same on shelf but has dropped from 400g to 340g has effectively raised its unit price by ~18% without a visible price increase. Tracking unit prices over time reveals shrinkflation across grocery categories.
Common Mistakes
- Comparing different quality tiers: The cheapest unit price isn't always best value — store brand eggs at $0.20 each vs. free-range $0.35 each is a genuine quality difference. Unit price comparison is valid for equivalent products.
- Buying more than you'll use: A bulk purchase at half the unit price is zero savings if half the product expires before use. Factor in realistic consumption rate and shelf life.
- Ignoring unit mismatches: Comparing price per ml vs. price per fl oz requires conversion. 1 US fl oz = 29.574 ml. Always convert to a common unit before comparing.
Frequently Asked Questions
Usually, but not always. Retailers sometimes use "economy" packaging as a loss leader (intentionally low price) while pricing mid-sizes competitively, or mark up large sizes knowing most consumers assume bigger = cheaper. Always calculate and compare. Store-brand large sizes often beat name-brand large sizes by 30–50% in unit price — the combination of own-label + large size typically wins.
Warehouse stores (Costco, Sam's Club) often have lower unit prices but higher absolute prices per item. Use unit price to verify whether the savings justify the membership fee. Divide annual membership cost ($50–120) by the number of shopping trips to calculate break-even savings per visit. For high-consumption staples (toilet paper, cooking oil, laundry detergent), warehouse unit prices typically beat supermarkets by 20–40%.
Shrinkflation is when manufacturers reduce product quantity while maintaining or slightly increasing the price — effectively a price increase disguised as no change. Detection methods: compare the net weight/volume on current packaging against a previous purchase; calculate current unit price vs. remembered price; track unit prices over time using a grocery price app. Common categories: cereal, toilet paper, chocolate bars, snacks, detergent, and paper towels have all seen significant shrinkflation in recent years.