Unit Price Calculator
Which product is really cheaper?
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Bigger pack doesn't always mean better value. Enter two products' prices and sizes and this calculator works out the true unit price — cost per gram, per millilitre, or per item — so you can see instantly which one is the better buy.
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How to Compare Unit Prices — The Quick Answer
Divide each product's price by its quantity to get the price per unit, then compare. Once both are in the same unit, the lower number is the better value — no matter which pack looks cheaper.
Shortcut
unit price = price ÷ quantity (compare the two figures in the same unit)
Which is the better buy?
| Product | Price | Size | Per 100 g |
|---|---|---|---|
| A | $3.50 | 500 g | $0.70 |
| B | $5.00 | 800 g | $0.63 |
| Result | B is cheaper |
Comparing '£ per 100 g' (or per litre, per item) is the fairest method because it normalises different pack sizes onto the same scale — exactly what supermarket shelf-edge unit prices do.
How It Works
The Method
Price normalised to a common unit
Formula
unit price = price ÷ quantity compare unit prices in the same unit — the lower one is better value
Variables
Normalising for size
Dividing the price by the amount gives what one unit costs, which lets you compare a 500 g pack against an 800 g pack fairly. Without this step, pack size tricks you into thinking the cheaper-looking package is the better deal.
Readable figures
Cost per single gram is a tiny decimal, so the calculator also shows the price per 100 units — the same convention used on supermarket shelf labels — which is far easier to compare at a glance.
Note: This compares value by quantity alone. It doesn't account for quality, waste (a bigger pack you don't finish), or storage — a cheaper unit price is only a good deal if you'll actually use it all.
Last updated: October 6, 2026
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Frequently Asked Questions
How do I work out the unit price?
Divide the price by the quantity. A $5.00 pack containing 800 g has a unit price of 5.00 ÷ 800 = $0.00625 per gram, which is $0.625 per 100 g. Compare that with the other product's per-100 g figure to see which is cheaper.
Is a bigger pack always better value?
Often, but not always. Bulk packs usually have a lower unit price, but not universally — sometimes a special offer on a smaller pack beats the large one on unit price. That's exactly why comparing the price per unit (rather than the total price) is the reliable way to decide.
Why compare per 100 g rather than per gram?
Per-gram prices are tiny decimals that are hard to tell apart ($0.00625 vs $0.007). Scaling to a common, larger base like 100 g — the standard on supermarket labels — makes the numbers readable and the comparison obvious.
Should I compare by weight or by volume?
Use whichever unit the product is sold in, and make sure both products use the same one. Comparing a liquid sold by volume against a solid sold by weight isn't meaningful — compare like with like, or convert to a common measure first.