Convert package mass to kilograms, calculate unit price, and compare different package sizes on an equal-mass basis.
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The calculation
Price per kg = total price ÷ net mass in kilograms
Worked example
750 g = 0.75 kg, so $9 ÷ 0.75 = $12/kg. A $16 package of 2 kg costs $8/kg. At a common 2 kg, the first rate would cost $24, which is $8 more. The second rate is one-third lower than the first.
Compare net contents using consistent currency, charges and discounts. A lower unit price does not establish quality or whether the larger package is useful.
Video chapters
- 0:00 — Lower price tag or lower price per kilogram?
- 0:16 — 750 g ÷ 1,000 = 0.75 kg
- 0:33 — $9 ÷ 0.75 kg = $12/kg
- 0:52 — $16 ÷ 2 kg = $8/kg
- 1:10 — Compare both at the same mass
- 1:29 — Percentage savings need a reference price
- 1:46 — Compare equivalent contents and costs
- 2:05 — Convert → divide → compare like quantities
Read the full transcript
A seven-hundred-fifty-gram package costs nine dollars. A two-kilogram package costs sixteen dollars. Which has the lower price for the same amount? The smaller package costs less at checkout, but unit price compares both offers using one common mass: a kilogram.
First put both masses in kilograms. One kilogram is one thousand grams, so seven hundred fifty grams divided by one thousand is zero point seven five kilograms. Use the net product mass. The weight of the box or container is not part of the contents you are comparing.
For the first package, divide nine dollars by zero point seven five kilograms. The unit price is twelve dollars per kilogram. You can check this by multiplying twelve by zero point seven five: that returns nine dollars. The calculation scales the price to a full kilogram without changing the rate.
For the second package, divide sixteen dollars by two kilograms. That gives eight dollars per kilogram. Splitting the contents into two equal one-kilogram portions also splits the sixteen-dollar price into two eight-dollar shares. The larger package has the lower unit price in this example.
At a common quantity of two kilograms, the first rate would cost twenty-four dollars, while the second costs sixteen. The difference is eight dollars. Per kilogram, the difference is four dollars. Always specify the matched quantity so a price difference is not confused with a package-price difference.
To express the unit-price saving relative to the first offer, divide four by twelve and multiply by one hundred. The second rate is about thirty-three point three percent lower. If you reverse the comparison, twelve is fifty percent higher than eight. The denominator changes with the reference offer.
Keep currency, discounts, taxes, and shipping on a consistent basis. Also check that the contents are comparable and that the extra quantity is useful to you. A lower price per kilogram describes cost per mass. It does not, by itself, decide quality, waste, or which purchase is best.
Convert the net mass to kilograms, divide total price by that mass, and compare the same currency per kilogram. Multiply back to check a package total. In our example, the two-kilogram package costs eight dollars per kilogram, compared with twelve for the smaller package.