A bulk pack can have a lower shelf unit price yet cost more per unit you actually use. Match the product and units, then divide the total purchase cost by the quantity you expect to use. This calculator also finds the bulk-use percentage needed to match the smaller pack.
- Small pack: 500 g, ₩6,000, all used
- Small pack effective cost: ₩1,200 per 100 g
- Bulk: 1,000 g, ₩10,000, 60% used → about ₩1,667/100 g
- Bulk break-even use: about 83.33%
Match units and comparable products. Cost does not establish performance or safety.
Hypothetical KRW example. The small pack is fully used; the bulk result changes with its estimated use percentage.
Calculate with your own numbers
Use the same unit, such as g or mL. A break-even use rate above 100% cannot be reached under these inputs.
This tool does not transmit your entries or store them on a server. The CSV is created in your browser. All sample numbers are hypothetical; use one currency and consistent units.
Package quantity and used quantity are different denominators
Package unit cost is total purchase cost divided by package quantity. Used-quantity cost divides the same total by quantity × expected use percentage. Include allocated shipping and taxes in the price. Compare grams with grams or millilitres with millilitres; do not convert between weight and volume without a valid density.
Use percentage is an estimate of consumption, not a quality, safety or effectiveness score. Base it on previous buying intervals and leftovers. If you have no records, test several explicit assumptions such as 50%, 75% and 100% instead of presenting one guess as a measured fact.
Allow for leftovers in the small pack too. The break-even percentage keeps the small pack's entered conditions fixed. A threshold above 100% means the bulk pack cannot match that cost even if you use all of it under these price assumptions.
Worked example: the lower package unit price loses
Hypothetical prices in KRW: a 500 g pack costs 6,000 and a 1,000 g pack costs 10,000. Using all the small pack costs 1,200 per 100 g. Using 60% of the bulk pack means using 600 g, so its effective cost is about 1,667 per 100 g—not its package price of 1,000 per 100 g.
Bulk buying breaks even at approximately 83.33% use. At 85% use it costs roughly 1,176 per 100 g, slightly below the small pack. The useful question is whether your realistic use exceeds that boundary, not whether bulk buying is usually cheaper.
Estimate consumption with a short record
- Record the previous purchase date, leftover quantity and use period.
- Adjust for changes in household size or habits.
- Check the manufacturer's storage and use instructions separately; savings do not justify exceeding them.
- For a shared purchase, enter your allocation and your share of delivery costs.
- Update the estimate after recording actual consumption.
Equal quantity does not guarantee equivalent products
Concentration, recommended dose, ingredients and convenience may differ. For concentrated products, also compare cost per use. The calculator does not judge food safety or product performance. Its answer depends on the purchase total, matching units and your consumption estimate.
Common questions
Is a bulk pack always cheaper if I finish it?
No. You still need to compare its total price and quantity with the smaller pack.
Does a remainder I will use next month count as waste?
No. Include a realistic plan to continue using it within the manufacturer's instructions, and record your time horizon.
Sources and how this guide was written
Background on unit pricing: the UK Competition and Markets Authority (CMA). Durudam developed the calculations and hypothetical examples in this guide.
Durudam prepared this calculation and record-keeping guide with AI assistance. It does not claim product testing or on-location reporting. Examples are hypothetical; formulas and assumptions are disclosed. Sources checked: 4 October 2026.
Related reading
What to check next in this situation
- Are Refills Better Value? Compare Cost Per Use, Not Just Volume
For concentrates or refills, compare the recommended quantity for the same task, not just the package size.