What this calculator does
Converting grams to calories only takes one fixed number: how many kilocalories a gram of that macronutrient releases when digested. Protein and carbohydrate both provide 4 kilocalories per gram, fat provides 9, and alcohol provides 7. These are the standard Atwater energy factors used on nutrition labels worldwide, and they do not change with brand, diet, or cooking method.
This calculator runs the conversion in either direction. Enter a number of grams of a chosen macronutrient to see its calories, or enter a calorie amount to see how many grams of that macronutrient it represents. It is deliberately narrow: for splitting a whole day’s calorie target across protein, carbs and fat by percentage, use the macronutrient split calculator instead.
The formula
For grams to calories, multiply the grams by the macronutrient’s energy factor. For calories to grams, divide the calories by that same factor. Fat carries more than double the energy of protein or carbohydrate per gram, which is why fatty foods are calorie-dense in small portions.
| Term | Meaning |
|---|---|
| Energy factor | Kilocalories released per gram: 4 for protein and carbohydrate, 9 for fat, 7 for alcohol. |
| Kilocalorie (kcal) | The unit used on nutrition labels, commonly just called a "calorie" in everyday food contexts. |
| Macronutrient | One of the three (or four, including alcohol) major categories of dietary energy source. |
The inputs explained
| Field | What to enter |
|---|---|
| Direction | Choose whether you are converting a known amount of grams into calories, or a known number of calories back into grams. |
| Macronutrient | The macronutrient the grams or calories belong to, since each has a different energy factor. |
| Grams (g) | Used when converting grams to calories. |
| Calories (kcal) | Used when converting calories to grams. |
When to use it
Reading a food label
A label lists grams of protein, carbohydrate and fat separately. Converting each to calories and adding them up cross-checks the label’s total calorie figure.
Working backwards from a calorie budget
If a meal plan allows 300 calories from fat, converting that to grams tells you how much fat, by weight, actually fits in that allowance.
Comparing energy density
Because fat carries more than double the calories per gram of protein or carbohydrate, converting a few sample amounts side by side shows why fatty foods pack more energy into a smaller portion.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How many calories are in different amounts of protein?
Grams of protein converted to calories across a range of common portion sizes.
How do 50 g of each macronutrient compare in calories?
The same 50 g amount, converted using each macronutrient’s own energy factor.
Questions
Why do protein and carbohydrate both use 4 kcal per gram?
These are the standard Atwater factors, based on how much usable energy the body extracts after digestion. Protein and carbohydrate happen to yield the same amount per gram, while fat yields more and alcohol sits in between.
Does cooking change the calories per gram?
No. The energy factor is a property of the macronutrient itself, not the cooking method. Cooking can change a food’s water content and therefore its calories per gram of the finished dish, but the factor for the pure macronutrient stays fixed.
Is this the same as counting calories for a whole food?
Not directly. Whole foods are a mixture of macronutrients plus water and fibre, so a food’s total calories come from summing each macronutrient’s contribution, not from a single factor applied to the food’s total weight.
How is this different from the macronutrient split calculator?
That calculator starts from a whole day’s calorie target and splits it into protein, carbohydrate and fat by percentage. This one converts a single, already-known amount of grams or calories for one macronutrient at a time.
To split a full day’s calorie target across protein, carbs and fat by percentage instead, see the macronutrient split calculator. To work out calories burned during exercise, try the calories burned calculator.