Unit Price Comparison Calculator
Two products in different packs, with different sizes, prices and units — which is actually the better deal? This tool normalises both sides to a price per base unit (gram, millilitre or each), shows them side by side, and reports the savings the cheaper option offers as well as how much more the pricier one costs. Weight (g · kg · oz · lb), volume (mL · L · fl oz · US gal) and count (each · dozen) are handled separately so weight is only ever compared to weight.
Same product in different sized packs? Enter the price, amount and unit for each option to see which is genuinely cheaper per unit.
Both price and amount must be positive numbers.
Result
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Computed per base unit (g, mL, each) so different package sizes can be compared apples-to-apples. Copy link to reproduce this comparison.
Formula
Unit price = price ÷ (amount × unit-to-base factor) Savings % = (dearer − cheaper) ÷ dearer × 100 Mark-up % = (dearer ÷ cheaper − 1) × 100
- · Base units: weight → gram (g), volume → millilitre (mL), count → each.
- · Weight conversions: 1 kg = 1000 g, 1 oz = 28.349523125 g, 1 lb = 453.59237 g (NIST avoirdupois).
- · Volume conversions: 1 L = 1000 mL, 1 US fluid ounce = 29.5735295625 mL, 1 US gallon = 3785.411784 mL (15 USC §205c).
- · Count conversion: 1 dozen = 12 each.
- · Both options must be in the same family (weight, volume or count). You cannot directly compare grams to millilitres without an ingredient density (use the Cooking Measurement Converter for that).
- · Strict unit-price comparison only — freshness, brand quality, expiry date, how much you will actually use, and other real-world factors are not modelled. A "cheaper per unit" jumbo pack is no bargain if half of it spoils.
- · Currency is purely a label — both sides must use the same currency. To compare across currencies, convert with an FX rate first.
Frequently asked
500 g for $10 vs 1 kg for $18 — which is the better deal?
Bring everything to a price-per-gram. $10 ÷ 500 g = $0.020 / g. $18 ÷ 1000 g = $0.018 / g. The 1 kg pack is 10 % cheaper per gram (you save $0.002 / g) — assuming you actually use it all. Plug both into the tool and you will see "✅ Option B is cheaper · saves 10.0 % · pricier one costs 11.1 % more". The 11.1 % comes from 0.020 ÷ 0.018 − 1 and reflects that "X % more" is always larger than the matching "Y % off" — a small but useful distinction when negotiating or comparing markups.
Why can I compare grams to pounds but not grams to millilitres?
Grams and pounds are both weight (same physical quantity), only different unit systems — converting is just a fixed factor (1 lb = 453.59237 g), so the tool can compare them directly. Grams measure mass; millilitres measure volume. Linking the two requires the substance’s density (g/mL): water = 1.000, all-purpose flour = 0.521, honey = 1.417, etc., all wildly different. This tool refuses cross-family comparisons by design — it would silently produce wrong answers. If you really need to compare grams to mL, use the Cooking Measurement Converter first to convert one side using the ingredient density.
Bigger packs are usually cheaper per unit — should I always buy the bigger one?
Not always. Cheaper-per-unit is just one dimension; weigh it against (1) consumption — saving 10 % on milk that goes off after a week is a loss, not a saving; (2) storage — bulk rice, paper, detergent are great if you have the room; (3) shelf life — coffee, flour and spices degrade, so buying ahead can hurt quality; (4) cash flow and curiosity — small packs let you trial brands or flavours cheaply. Rule of thumb: "won't spoil + you'll definitely use it + you have the storage" → buy big; otherwise "cheaper per unit" is not the same as "better value".
The tool says "saves 10 %" and "costs 11.1 % more" — why are the two percentages different?
The two percentages have different bases. "Saves 10 %" = (dearer − cheaper) ÷ dearer — measured against the dearer side. "Costs 11.1 % more" = (dearer ÷ cheaper) − 1 — measured against the cheaper side. Example: $0.020 / g vs $0.018 / g. From dear to cheap, saving = (0.020 − 0.018) ÷ 0.020 = 10 %. From cheap to dear, mark-up = 0.020 ÷ 0.018 − 1 = 11.11 %. Smaller base ⇒ bigger percentage. The same asymmetry is why a stock that drops 50 % needs a 100 % gain to break even — useful context whenever a marketer quotes a "% off" figure.
How do Hong Kong supermarket shelf labels show unit prices?
Hong Kong supermarket chains like PARKnSHOP and Wellcome usually print a small "$X.XX / 100 g", "$X.XX / 100 mL" or "$X.XX / each" line under the headline price on their electronic shelf labels. When labels are missing or use mismatched bases (one per 100 g, one per kg), this tool gives you the answer faster than mental maths — and it supports more units than the PARKnSHOP app, including the oz / lb / fl oz / US gal sizes that show up on overseas e-commerce listings. No login required.
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