Unit Price Comparison

The one number that survives packaging

Shelves are arranged to defeat comparison: a small bag here, a family pack there, a 1.4 kg tub with a suspicious round price. The unit price is the only figure that ignores all of it — money per gram, per millilitre, per sheet — and this page computes it for two products at once, then states which is cheaper and by how many per cent. Where shop labels disagree in units, overlap in bundles or hide the quantity in fine print, a per-unit comparison is the only tool that reduces the argument to one number on either side.

The per cent is not decoration. A product that is cheaper by 2% is a shrug; cheaper by 40% is a change of brand. The tool prints the gap as "Product B costs 11.11% less per unit", which is exactly the figure worth carrying out of the aisle — and exactly the figure most price tags never state.

A worked example, step by step

Problem: rice A costs 3.20 for a 2 lb bag; rice B costs 7.50 for a 5 lb bag. Both prices are in pounds, so units already agree. Which is the better buy?

1. A: 3.20 ÷ 2 = 1.60 per pound.
2. B: 7.50 ÷ 5 = 1.50 per pound. B is cheaper per unit.
3. Gap: (1.60 − 1.50) ÷ 1.60 × 100 = 6.25% less per pound for B.
4. Total buy: 5 lb of B at 7.50 versus 2.5 bags of A at 3.20 = 8.00. B also wins on the trip to the till.
5. Reality check: if you only need 2 lb this month, A at 3.20 beats buying 5 lb of B for a table for one — unit price compares value, not your actual need.

Both answers belong in the shopping bag: the per-pound gap tells you which brand to load the trolley with; the need tells you which pack size to actually pick up. The tool's default pair makes the same point in grams — 4.50 for 500 g is 0.009 per gram, 8.00 for 1,000 g is 0.008 per gram, the larger pack 11.11% cheaper per gram — a difference that compounds fast when the family eats rice three times a week.

Per-unit prices for one product line

Suppose the same rice is sold in four pack sizes. Compute the unit price once and rank the pack sizes by it:

The tie at the top is the instructive row: at 6.30 and 8.40 the per-gram price is identical, so hierarchy by unit price breaks — and other criteria (storage, freshness) decide. A shelf that keeps getting cheaper per gram as it gets bigger is normal; a shelf where the middle size is cheapest per gram is where the comparison works hardest.

Cross-unit and cross-brand checks

The comparison needs the same unit, not the same product shape. Litres against millilitres, grams against kilograms, single rolls against multi-packs — convert first, then compare. Two honest traps: a "50% free" bonus pack increases quantity, not price, so the unit price falls by slightly more than thirty per cent, not fifty; and a buy-one-get-one-half-price does not halve the per unit price, it multiplies the quantity by 1.5 at the same total price, which means each unit costs 2 ÷ 3 of the label price per unit. Run the offer's arithmetic through this page rather than through the sticker's claim, and the shelf stops lying.

Mistakes that quietly cost money

• Comparing different units. 500 g against 1 kg needs conversion first; per-unit prices of mixed units are meaningless.
• Comparing different states of a product. Fresh versus frozen, or wet versus dry weight, are different products wearing similar labels.
• Trusting "family" wording. Large packs are usually cheaper but not always; the shelf optimises revenue, not your kitchen.
• Forgetting spoilage. A per-unit winner you throw away loses to the per-unit loser you finish.
• Quoting the saving without the percentage. "2 cents less per gram" hides whether it is 10% or 0.1%; the percentage is the comparable claim.

Keep exploring

• VAT Calculator — add tax to either option before comparing, when prices are quoted ex-VAT.
• Discount Calculator — apply the shelf's offer to a base price before ranking packs.
• Stacked Discounts — stack two or three discounts and get the true combined cut.
• Guide: VAT and Sales Tax Explained.