Bulk Buy Detective
Does buying bulk actually save money? Scan to find out.
Item A (The Small One?)
Item B (The Bulk One?)
per unit by choosing the winner
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What this calculator does
Bulk Buy Detective compares two packages of the same product and tells you which one costs less per ounce, gram, liter or item, and by how much. It converts between US and metric units for you, so a 12 oz bag can be compared fairly with a 3 lb bag, or a 2 L bottle with a 1 gallon jug.
How to use it
- For Item A, enter the shelf price and the net quantity printed on the package, then pick its unit.
- Do the same for Item B.
- Press Print Receipt. The receipt names the cheaper item, shows its price per unit, and shows how much less it costs per unit than the other one.
Both items must be measured the same way: both by weight, both by volume, or both by count. A weight can't be compared with a volume without knowing how dense the product is.
How it's calculated
Each quantity is first converted to a common base: grams for weight, milliliters for volume, single items for count. Then:
unit price = price ÷ quantity in base units
savings % = (higher unit price − lower unit price) ÷ higher unit price × 100
The conversions use the standard definitions: 1 oz = 28.3495 g, 1 lb = 453.592 g, 1 US fl oz = 29.5735 mL, 1 US gallon = 3,785.41 mL.
A worked example
A 12 oz bag of coffee costs $4.99 and a 3 lb bag costs $14.50:
- Small bag: $4.99 ÷ 12 oz = $0.416 per ounce
- Large bag: 3 lb is 48 oz, so $14.50 ÷ 48 oz = $0.302 per ounce
- The large bag costs ($0.416 − $0.302) ÷ $0.416 = 27.4% less per ounce
Why the bigger package isn't always cheaper
Most shoppers assume larger packages carry a lower unit price, and usually they do. But not always: sale prices and coupons often apply only to the smaller size, "family size" packaging is sometimes priced higher per unit, and package sizes can shrink while the price stays the same. Many stores print a unit price on the shelf tag, but they don't always use the same unit for every size (per ounce on one tag, per pound on another), which makes a fair comparison hard to do in your head.
When buying in bulk isn't worth it
A lower unit price only saves money if you use everything you buy. Bulk can cost more overall when:
- The food spoils before you finish it. Our Food Shelf Life Encyclopedia shows how long common foods keep once opened.
- You don't have room to store it, or it goes stale in the pantry.
- The bigger package tempts you to use more than you normally would.
Frequently asked questions
How do I compare paper towels or toilet paper?
Compare by sheet count rather than roll count, since a "double roll" can mean anything. Choose Items / Count and enter the total sheets (rolls × sheets per roll). If the sheet sizes differ, compare the total area printed on the package instead.
Should I enter the price before or after a coupon?
Enter what you'll actually pay. If a coupon applies to only one size, use the discounted price for that item.
Can I compare a liquid sold by weight with one sold by volume?
Not with this tool, because the answer depends on the product's density. For water-like liquids, 1 mL weighs about 1 g, so a rough comparison is possible, but oils, syrups and detergents differ.
Does it work in other currencies?
Yes. The math is the same for any currency; the dollar sign is just a label.
Sources: Unit definitions from NIST Special Publication 811, Appendix B.8. Last reviewed on SuiteWebTools: October 2026.