Unit Price Calculator
Compare unit prices to find the best deal. Add multiple products and see which offers the lowest cost per unit.
Unit Price Comparison
Why Unit Price Is the Only Number That Matters
A 500g bag of rice for £1.20 vs a 1kg bag for £2.10 — which is cheaper? Your instinct says the bigger bag, but the maths says the smaller one. The 500g bag costs £2.40/kg. The 1kg bag costs £2.10/kg. The larger pack wins by 30p per kilo.
Supermarkets are legally required to show unit prices on shelf labels in the UK. But the labels are often in different units (per 100g vs per kg), tiny print, or missing entirely online. This calculator normalises everything so you can compare properly.
The biggest savings come from comparing across brands and pack sizes. Own-brand products are typically 20-40% cheaper per unit than branded equivalents. But not always — check, don't assume.
Real Supermarket Comparisons
Here's how unit pricing reveals the actual best deal (typical UK prices):
| Product | Pack Price | Size | Unit Price | Winner? |
|---|---|---|---|---|
| Branded cereal | £3.50 | 500g | £7.00/kg | No |
| Own-brand cereal | £1.20 | 500g | £2.40/kg | Yes — 66% cheaper |
| Small washing-up liquid | £1.00 | 450ml | £2.22/litre | No |
| Large washing-up liquid | £1.50 | 900ml | £1.67/litre | Yes — 25% cheaper |
Supermarket Tricks to Watch For
Unit switching
One product shows price per 100ml, the next per litre, a third per item. This makes mental comparison nearly impossible — which is exactly the point. Always normalise to the same unit.
"Family size" premium
Larger packs are usually cheaper per unit, but not during promotions. Supermarkets sometimes discount the medium pack below the bulk unit price. Always check — don't assume bigger is better.
Shrinkflation
Same price, smaller pack. A chocolate bar that used to be 200g is now 180g at the same price. That's an 11% price increase disguised as "new look, same great taste." Unit pricing catches this instantly.
Smart Shopping Tips
- Factor in waste. A 2kg bag of salad at half the per-gram price is no bargain if half ends up in the bin. Buy quantities you'll actually consume.
- Consider performance, not just price. A £3 bottle of detergent that lasts twice as long as a £2 one is better value per wash. Unit price per use matters more than unit price per gram for some products.
- Compare across stores. The cheapest option in one supermarket might be more expensive than the mid-range in another. Unit price lets you compare across stores on equal terms.
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How to use this tool
Enter the price and quantity for each product
Set the unit of measurement
The best value is highlighted automatically
Common uses
- Comparing supermarket products of different sizes
- Finding the best value across different brands
- Checking whether multi-buy offers are genuine deals
- Comparing prices across different shops
- Working out whether bulk buying saves money
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