Price Per 100g Calculator

Why the cost per 100 grams is the number that matters

A shelf tag tells you what one package costs. It does not tell you what you pay for the food inside. Two bags of the same snack can sit side by side, one at $4.29 for 340 grams and one at $5.99 for 1.5 pounds, and the bigger bag wins by a wide margin even though it costs more at the register. The only way to see that at a glance is to put both prices on the same weight.

Grams work well for that because 100 grams is a size you can picture: a little less than a quarter pound, about one skinless chicken thigh, a small handful of nuts. Metric unit pricing also shows up on more US shelves than people expect. Bulk bins, imported cheese, deli salads and coffee often carry a per 100 gram figure right next to the total.

Once you have the number, comparisons get easy. Rice at 30 cents per 100 grams costs $3.00 a kilo. The same rice in a smaller bag at 45 cents per 100 grams costs $4.50 a kilo. You do not need to hold both bags or do long division in the aisle to see which one is the better buy.

The three step formula

Price divided by weight in grams, then multiplied by 100. That is the whole method.

Example one: a 340 gram bag of almonds at $4.29. Divide 4.29 by 340 to get 0.012618 per gram, then multiply by 100 for 1.26. The cost is $1.26 per 100 grams, which is $12.62 per kilo.

Example two: an 8 ounce block of cheese at $2.49. Eight ounces is 226.8 grams. 2.49 / 226.8 x 100 = 1.10, so the cheese runs $1.10 per 100 grams, or $4.98 per pound.

Do it in the other order if that feels easier: work out the price per gram first, then move the decimal two places to the right. A package at 1.26 cents per gram is $1.26 per 100 grams. Same answer, less writing.

Round at the end, not in the middle. Rounding 4.29 / 340 down to 0.01 per gram turns a $1.26 result into $1.00, a 20 percent error, and an error that big can flip which package looks cheaper.

Reading the weight on the package

US labels give net weight in ounces and pounds, with grams in smaller print. Convert before you divide, or the answer will be off by a factor of 28.

Two shortcuts cover most of the shelf. A 12 ounce bag is 340.2 grams, so close to 340 that you can treat it as the same size. A one pound bag is 453.6 grams, which is 4.54 units of 100 grams.

Watch the difference between fluid ounces and weight ounces on liquids. A 12 fl oz bottle of dressing is volume, not weight, and a per 100 gram figure will be wrong unless you know how dense the liquid is. For anything sold by volume, compare price per fluid ounce or per quart instead.

Worked example: almonds in two packages

Bag A is 340 grams at $4.29. Bag B is 1.5 pounds at $5.99. On the shelf, B looks like the expensive one. Per gram of food, it is the cheap one.

Bag A: 4.29 / 340 x 100 = 1.26, so $1.26 per 100 grams, which is $5.72 per pound. Bag B: 1.5 lb is 680.4 grams, and 5.99 / 680.4 x 100 = 0.88, so $0.88 per 100 grams, which is $3.99 per pound.

The gap is $0.38 per 100 grams. Bag A costs 43 percent more for the same nuts. A household that goes through 2 pounds of almonds a month buys 24 pounds a year: $137.28 at the Bag A rate against $95.76 at the Bag B rate, a difference of $41.52 for the year.

That is the whole case for doing this math once. The number does not change much week to week, so a single check on a staple you buy often pays you back all year. Run your own two packages through the calculator above and it will show both rows, plus which one wins and by how much.

Where 100 gram pricing goes wrong

Three traps are common enough to check every time.

Drained weight. A can of tomatoes lists 400 grams net and 240 grams drained. At $1.89 the net figure works out to $0.47 per 100 grams, but you eat the drained part, which is $0.79 per 100 grams. Two cans with the same net weight can hold far different amounts of food once the liquid is poured off.

Shrinkflation. The price stays and the package shrinks. A box that drops from 500 grams to 450 grams at the same $3.49 goes from $0.70 per 100 grams to $0.78, an 11 percent increase that never shows up as a price change on the tag.

Added water and brine. Frozen chicken and some hams are sold with a solution added. The label has to say so, but the net weight includes the water. A 10 percent solution means you are paying meat prices for the liquid that cooks off.

None of this makes the per 100 gram figure useless. It means the figure describes the package, and you still have to read what the package says it contains.

Cost per 100 grams across common package sizes

The grid below shows how the same four prices land on four package sizes. Read across a row to see what a bigger package buys you, and down a column to see the effect of price.

The jump from 250 grams to 500 grams halves the unit price at any given price point, which is why the small box is rarely the right buy for anything shelf stable. The jump from 500 grams to 1 kilo halves it again, but only if you will finish the food before it goes stale.

What the number does not include

Unit price compares food, not trips. Sales tax, delivery fees, membership fees and spoilage all sit outside the figure, and any of them can wipe out a 30 percent gap.

Sales tax applies to the total, so a $1.26 per 100 gram figure becomes about $1.36 at 8.25 percent. Delivery changes the picture faster: a $9.99 delivery fee on a single 340 gram bag adds $2.94 per 100 grams, which is more than the food itself.

Spoilage is the quiet one. A 1 kilo bag at $0.30 per 100 grams is a bargain only if you use it. Throw away a third of it and the effective price climbs to $0.45, right back to the 500 gram rate.

For the rules behind the numbers on the label, the NIST Handbook 130 covers unit pricing and net quantity rules that US stores follow. The FDA food labeling pages explain what net weight has to include, and USDA Market News publishes retail price reports if you want a second opinion on whether a price is normal for the season.