Bulk buy calculator
Type the price and size of the smaller pack and the bigger one, and how much of the bigger pack you expect to throw away, and this bulk buy calculator tells you which is really cheaper for the amount you'll use. It also gives the break-even: the most you can waste before the bigger pack stops being the better buy. Nothing you type leaves your browser.
How it works
A bigger pack usually costs less per ounce. But you pay for the whole pack, and you only get value from the part you eat. So the calculator compares:
- the smaller pack's price per unit, and
- the bigger pack's price per unit of what you actually use, which is its price divided by the amount you don't throw away.
Take the example the calculator opens with. 16 oz for $3.49 is about 21.8 cents an ounce. 64 oz for $9.99 is about 15.6 cents an ounce, 28.4% cheaper. If a tenth of the big pack goes in the bin, you're paying $9.99 for 57.6 oz, which is about 17.3 cents an ounce: still cheaper, by $2.57 a pack against buying the same amount in small packs.
The rule of thumb
The bigger pack wins as long as the share you throw away is smaller than its discount. At a 28.4% discount, you can waste up to about 28% of the big pack before the small one would have been cheaper. At a 10% discount, only 10%.
That's why bulk works well for rice, pasta, oats, canned goods, frozen vegetables and household supplies, where the waste is close to zero, and badly for salad leaves, berries, bread and soft cheese in a small household. Is buying in bulk cheaper sets the rule out with a full break-even table, and is a Costco membership worth it adds the membership fee. If a warehouse club is where the bigger packs come from, the Costco membership calculator checks whether the fee pays for itself at your spend and waste.
Units
The two packs can be in different units of the same kind: ounces against pounds, grams against kilograms, fluid ounces against litres, or a count against a count. The calculator converts with exact US and metric factors and shows the price per the smaller pack's natural unit. It won't compare a weight with a volume, because that needs the density of the food, and a guessed density would give a confident wrong answer.
For comparing more than two sizes, or products from different brands, the unit price calculator handles up to six at once.
Getting the waste share right
The waste share is the number people leave at zero, and it's the one that decides the answer. If you're not sure, think about the last time you bought the big pack: how much was left when it went off, or went stale, or got thrown out at the back of the fridge? A quarter of a bag of spinach is 25%.
For a household-wide figure, our food waste calculator turns what you throw away into a yearly cost, and food waste statistics has the national figures.
Common questions
How do I know if buying in bulk is cheaper?
Compare the price per unit of the two packs, then divide the bigger pack's price by the share you'll actually use. If that's still lower than the small pack's price per unit, the bigger pack is cheaper.
How much waste makes bulk buying not worth it?
Any share bigger than the bulk discount. If the big pack is 20% cheaper per unit and you throw away more than 20% of it, the small pack would have cost less.
Is the bigger pack always cheaper per unit?
No. Stores sometimes price the bigger pack higher per unit, and a sale on the small pack can reverse the usual order. The calculator shows when the bigger pack costs more per unit before any waste.