Formula
Portion value = value per 100g × grams eaten ÷ 100. The calculator applies the same multiplier to each number you enter.
Example
For 65g of a food with 240 calories per 100g, the multiplier is 0.65 and the result is 156 calories. If the label also lists 12g protein per 100g, the portion contains 7.8g protein.
Choose one consistent label column
Only enter values from the column headed "per 100g." Do not mix them with calories or macros from a "per serving" or "per pack" column. If the label gives values for one serving and your portion weighs something else, use the serving size and portion calculator. If this is a meal you repeat, use the weighed repeat meal calculator to save the gram-based result as an editable Mori entry.
Read how to calculate nutrition per 100g for any portion for examples and mistakes worth checking. To compare the energy in two foods at equal weight, use the food calorie density calculator. The broader nutrition-label guide explains how to choose between per-serving, per-package, per-100g, and per-100ml columns.
Going the other way: how many grams is 100 Calories?
The calculator answers this too, in the last result row. Divide 10,000 by the calories per 100g and you get the weight that carries 100 Calories.
It is a useful sanity check because the answer varies so much. At 240 Calories per 100g, 100 Calories is about 42g. For olive oil at 884, it is about 11g, a little under a tablespoon. For broccoli at 34, it is about 294g, roughly half a large head. Same 100 Calories, wildly different amounts of food.
If you want that comparison across a range of everyday foods rather than one label at a time, how many calories are in 100 grams sets thirteen of them side by side.
Most labels describe the food as sold, not as eaten
This is the mistake that costs the most calories, and the arithmetic on this page cannot catch it. A pack of raw chicken is labelled per 100g raw. A bag of dry rice is labelled per 100g dry. If you weigh the food after cooking and apply the label figure, the two numbers describe different things.
Meat loses water and gets lighter, so 100g cooked came from noticeably more than 100g raw, and applying the raw label to the cooked weight undercounts. Rice and pasta absorb water and get heavier, so applying the dry label to the cooked weight badly overcounts: 100g of cooked rice came from roughly 33g dry.
Pick one state and stay in it. Weighing raw and using the label as printed is usually simplest. If you need to move between the two, the raw to cooked weight calculator converts them, and the raw versus cooked guide covers which state to standardise on.
Canned and jarred food: check whether the label is drained
Tinned beans, tuna, sweetcorn, olives and similar products are packed in liquid, and the nutrition panel may describe the contents including that liquid rather than the solids you actually eat. Packs often print a net weight and a drained weight, and the nutrition column does not always tell you which one it belongs to.
If you drain the tin and weigh what is left, use a drained-basis figure where the label provides one. Where it does not, treat the result as rougher than usual rather than assuming it transfers cleanly. This is a case where the printed number and the food in your bowl genuinely are not the same thing.
Per 100ml is not per 100g
Drinks, oils, sauces and dairy are often declared per 100ml. Millilitres measure volume and grams measure weight, and the two only match for something with the density of water.
Oil is lighter than water, so 100ml of oil weighs about 92g. Honey and syrups are heavier, so 100ml weighs well over 100g. Entering a gram weight against a per-100ml label introduces an error in whichever direction that food happens to differ.
The fix is to stay in one unit. If the label says per 100ml, measure in millilitres. If you only have a scale, use a per-100g label where the product offers one. If the label is in ounces rather than grams, the ounces to grams guide covers that conversion and the ounce versus fluid ounce trap.
What usually goes wrong
In rough order of how much they cost:
- Applying a raw or dry label to a cooked weight, or the reverse.
- Mixing a per-100g figure for one nutrient with a per-serving figure for another. Take every value from the same column.
- Weighing with the plate or container still on the scale.
- Entering grams against a per-100ml declaration.
- Scaling the energy figure and leaving protein, carbohydrate and fat at their label values. Every number moves by the same multiplier.
- Forgetting the oil, butter or sauce added during cooking. None of it is on the label of the thing you weighed.
The last one is usually the largest single gap in a home-cooked log, and the cooking oil calorie calculator handles it separately.
When a food database entry looks wrong
People often land on this calculator because a tracker entry does not match the package in front of them. Check the basis before you trust or reject the entry: per 100g, per serving, per package, cooked, raw, drained, dry, or prepared.
If the entry gives calories per serving but your label gives calories per 100g, convert both to the same basis before comparing. If the food is generic rather than branded, compare it with a close USDA FoodData Central entry and expect some variation. The food database entry checker guide gives a longer audit path for entries that look too low or too high.
What the result means
The output is only as precise as the label and portion weight you enter. Packaged food values can be rounded, and the product itself can vary. Treat the result as a practical journal estimate, not a laboratory measurement or medical instruction.
For a liquid labeled per 100ml, use millilitres throughout. Do not enter a gram weight here unless you have a reliable density conversion.
If you are trying to picture the weight rather than scale a label, how many calories are in 100 grams compares thirteen common foods at that weight and shows roughly what each one looks like.