Check Unit Prices to See Whether Bundles and Bulk Buys Are Really Cheaper
“Buying more is cheaper” is not always true. Items can often cost more per unit simply because they are sold as a bundle. The only way not to be fooled is to convert the price to the same basis, such as “per item,” “per 1g,” or “per 1ml,” and compare. This is called the unit price.
| Section | Key summary |
|---|---|
| Introduction | “Buying more is cheaper” is not always true |
| Unit price calculation is just one division | If 30 rolls cost 21,000 won, that is 700 won per roll |
| A 5-second check sequence | Choose 2 products to compare, such as a small size vs a large size |
| When you should not buy even if it is cheaper | Sometimes you lose money even when the unit price is lower |
| Apply this only to these types of items | Short-shelf-life items: milk, tofu, bread → buy only what you can use within 1~2 weeks |
| Bulk sizes are cheaper only when you can use them all | Short key point |
Unit price calculation is just one division
The formula is “total price ÷ total quantity.” If 12 rolls of toilet paper cost 9,600 won, that is 800 won per roll. If 30 rolls cost 21,000 won, that is 700 won per roll. The 30-roll pack is 8% cheaper. Conversely, if 1L of detergent costs 4,500 won (4.5 won per 1ml) and 2.5L costs 12,000 won (4.8 won per 1ml), the bulk size is actually more expensive. The numbers make it clear that a bundle is not automatically a better deal.
A 5-second check sequence
- Choose 2 products to compare, such as a small size vs a large size.
- For each one, calculate the unit price with “price ÷ quantity (items, g, or ml).” If mental math is hard, use your phone calculator.
- Choose the one with the lower unit price. If the difference is under 5%, buy the larger one only when you are confident you will use it all.
- Check the expiration date and storage space last.
When you should not buy even if it is cheaper
Sometimes you lose money even when the unit price is lower. If a 2.5kg bulk sauce is 20% cheaper per unit than a 1kg bottle, but you can only use half before the expiration date and throw the rest away, the actual unit cost becomes twice as high. In other words, “unit price × the proportion you will actually use” is the real cost. Buying a 5kg bundle of a spice you use only 1kg of per year is a loss no matter how cheap it looks.
Apply this only to these types of items
- Things that do not spoil and are used daily: toilet paper, detergent, rice, bottled water → actively compare bulk sizes
- Short-shelf-life items: milk, tofu, bread → buy only what you can use within 1~2 weeks
- Taste-dependent items: snacks or sauces you are trying for the first time → test with a small size first
Bulk sizes are cheaper only when you can use them all
Bundles look cheap because the total sticker price is larger, but the real judgment should be based on unit price. When you divide the cost by per item, per 100g, or per 100ml, the smaller package may sometimes be cheaper.
Even if the unit price is low, it is a loss if you lack storage space or cannot use it before the expiration date. Bulk buying works well for daily necessities you use often, but for sauces, snacks, and fresh foods, you also need to consider the risk of waste.