Normalize different package sizes to an equal 100-gram basis, compare the unit prices, and check how net weight and waste affect the decision.
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The calculation
Price per 100 g = total price ÷ net weight in grams × 100
Worked example
A 400 g package at $4.80 costs $1.20 per 100 g. A comparable 600 g package at $6.60 costs $1.10 per 100 g. The larger package is ten cents cheaper per 100 g but costs $1.80 more upfront.
Compare like products using the net amount actually usable; price per 100 g is a value comparison, not a quality rating, and a larger pack can be wasted.
Video chapters
- 0:00 — Different packages, one basis
- 0:13 — Split the first pack
- 0:26 — Write the reusable formula
- 0:39 — Normalize the second pack
- 0:53 — Compare equal amounts
- 1:08 — Check weight and price definitions
- 1:22 — Know what the number misses
- 1:35 — Recap the equal-unit method
Read the full transcript
Which is cheaper: four hundred grams for four dollars and eighty cents, or six hundred grams for six dollars and sixty cents? The shelf prices are different, and so are the amounts. To make a fair comparison, we will price the same one-hundred-gram portion of each product.
Four hundred grams contains four portions of one hundred grams. Spread the four dollars and eighty cents evenly across those four portions. Each tile receives one dollar and twenty cents. That is the first package's price per one hundred grams.
The general method is total price divided by net weight in grams, then multiplied by one hundred. Four dollars and eighty cents divided by four hundred grams is one point two cents per gram. Multiply by one hundred grams, and the answer is one dollar and twenty cents.
Now divide six dollars and sixty cents by six hundred grams, then multiply by one hundred. The second package costs one dollar and ten cents per one hundred grams. Six equal tiles of one dollar and ten cents rebuild the original six-dollar-and-sixty-cent price.
At the same one-hundred-gram scale, one dollar and ten cents is ten cents below one dollar and twenty cents. So the six-hundred-gram pack has the lower unit price. It still asks you to pay six dollars and sixty cents now, versus four dollars and eighty cents for the smaller pack.
Use the price you actually pay and the net weight of the product, excluding the container. If a sale requires two packs, combine the sale price and both net weights. And if you eat only a drained or peeled portion, shelf weight may be the wrong comparison base.
A lower price per one hundred grams does not guarantee a better purchase. The products need to be comparable, and you need to use the amount you buy. Spoilage, quality, ingredients, or a different strength can outweigh a small unit-price saving.
Convert the net weight to grams, divide total price by that weight, and multiply by one hundred. In our example, four hundred grams at four dollars and eighty cents gives one dollar and twenty cents per one hundred grams; six hundred grams at six dollars and sixty cents gives one dollar and ten cents. Compare those equal units, then make the practical choice.