Unit Price Calculator
Compare any number of pack sizes per unit, and see how much of the big one you can throw away before it stops being the cheaper buy.
Quantities must be in the same unit for the comparison to mean anything — ounces against ounces, not ounces against count. Nothing is uploaded.
What you can afford to waste is exactly what you save
A 24 oz jar at $5.00 is 16.7% cheaper per ounce than a 12 oz jar at $3.00. Throw away more than 16.7% of the big one and the small one was the better buy. Those are the same number, and they are the same number for every pair of packages: the share of the larger pack you can afford to bin is exactly the share you save per unit.
| If you waste | The big one really costs | The small one costs | |
|---|---|---|---|
| 0.0% | $0.2083/oz | $0.2500/oz | big one wins |
| 5.0% | $0.2193/oz | $0.2500/oz | big one wins |
| 10.0% | $0.2315/oz | $0.2500/oz | big one wins |
| 15.0% | $0.2451/oz | $0.2500/oz | big one wins |
| 20.0% | $0.2604/oz | $0.2500/oz | small one wins |
| 30.0% | $0.2976/oz | $0.2500/oz | small one wins |
Which turns a question you cannot answer — is the big one worth it? — into one you can, because you have a rough idea how much of the last big jar went in the bin. If the saving is 17% and you reliably bin a quarter of it, the small jar is cheaper and always was.
The biggest pack is not reliably the cheapest
On this shelf the cheapest per ounce is the Twin pack, 16 oz, not the Bulk, 64 oz, which costs 13.0% more per ounce than it. Nor is it the smallest. The per-unit price falls and then rises again, so neither "buy the big one" nor "buy the small one" finds it — only reading the number does.
| Pack | Price | Per ounce | |
|---|---|---|---|
| Single, 8 oz | $2.29 | $0.2863 | |
| Twin pack, 16 oz | $3.98 | $0.2487 | cheapest per ounce |
| Family, 32 oz | $8.49 | $0.2653 | |
| Bulk, 64 oz | $17.99 | $0.2811 |
Wasting the same share of every pack does not change which one wins, since it scales all of them alike. It is only when the waste falls unevenly — which it does, because the big pack is the one that goes off before you finish it — that the ranking moves.
How to use
- Enter each pack size with its price and quantity.
- Read the cheapest per unit.
- Add the share of the largest pack you expect to throw away.
- Watch whether the ranking survives it.
Frequently asked questions
How much of the bigger pack can I waste before it stops being worth it?
Exactly the fraction you save per unit by buying it. A 24oz jar at $5.00 is 16.7% cheaper per ounce than a 12oz jar at $3.00, so binning more than 16.7% of the big jar makes the small one cheaper. Those two numbers are the same number for every pair of packages, which turns an unanswerable question into one you can estimate.
Is the biggest pack always cheapest per unit?
No, and it is wrong often enough to be worth checking every time. On the shelf shown here the 16oz twin pack is cheapest per ounce, the 32oz costs more than it, and the 64oz costs more still. The per-unit price falls and then rises, so neither buy-the-big-one nor buy-the-small-one finds the answer.
Why does waste change the ranking at all?
Because unit price divides by the quantity on the label, and what you actually pay per unit divides by the quantity that reaches you. Throw a third of a pack away and the real price per unit is half as much again. It only matters when the waste falls unevenly — wasting the same share of every pack scales them all alike and leaves the ranking untouched.
What if the packs are measured differently?
They have to share a unit for the comparison to mean anything. Ounces against ounces or count against count; ounces against count gives a number with no interpretation. Convert one side before entering it.
Does buying in bulk save money?
It saves money on the units you use. The honest test is whether the per-unit discount is larger than the share you expect to waste, and for perishables it frequently is not. For things that do not spoil, the discount is real and the answer is usually yes.
What about the money tied up in a big pack?
Not modelled here, and worth a thought if the pack is large enough to matter. Buying a year of something at once is a real cost in cash you cannot spend elsewhere, on top of the storage it needs. This calculator answers the narrower question of price per unit actually used.
Can I compare more than two sizes?
Yes — add as many as the shelf has. They are ranked by unit price, with the cheapest highlighted, and the largest pack additionally shown at its effective price after waste.
Does this send anything anywhere?
No. Every figure is computed in your browser, and nothing is uploaded or stored.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.