Grams to Calories Converter
Convert grams of fat, protein, and carbohydrates to calories (kcal) using the Atwater general factors — for nutrition and diet planning.
Reviewed October 7, 2026 Runs in your browser — inputs are never stored
Total calories
500.0 kcal
Fat (×9)
180.0 kcal
Protein (×4)
120.0 kcal
Carbs (×4)
200.0 kcal
Caloric density (per gram)
| Macronutrient | kcal/g | kJ/g |
|---|---|---|
| Fat | 9 | 37.7 |
| Protein | 4 | 16.7 |
| Carbohydrates | 4 | 16.7 |
| Alcohol (ethanol) | 7 | 29.3 |
| Fibre (insoluble) | 0 | 0 |
This tool provides general unit conversions for everyday and educational use. For regulated, legal, or scientific applications, verify conversion factors against the applicable official standard.
About the Grams to Calories Converter
The grams to calories converter turns grams of fat, protein and carbohydrate into calories with the Atwater factors: 9 kcal per gram of fat and 4 kcal per gram of protein or carbohydrate. It shows the total and the share of calories from each macronutrient, which is how nutrition labels are calculated.
How to use it
- 1Enter grams of fat.
- 2Enter grams of protein.
- 3Enter grams of carbohydrate and read the total calories and macro split.
Worked example
20 g fat × 9 + 30 g protein × 4 + 50 g carbohydrate × 4 = 180 + 120 + 200 = 500 kcal. Fat provides 36% of the calories.
How it works
Atwater factors
Fat: 9 kcal/g · Protein: 4 kcal/g · Carbohydrates: 4 kcal/g · Alcohol: 7 kcal/g. These are the internationally accepted physiological fuel values.
Common use cases
- Checking nutrition labels
- Planning meals with macronutrient targets
- Recipe nutrition estimates
Frequently asked questions
A:Fat has 9 kcal/g vs 4 kcal/g for protein/carbs because fat has more C-H bonds per unit mass (higher energy density).
A:These are kilocalories (kcal). On food labels, "Calories" (capital C) = kcal. 1 kcal = 1,000 scientific (small) calories.
Reviewed for accuracy · Last updated October 7, 2026
Conversion factors are based on internationally defined SI units and standard metric/imperial equivalence tables.
CalcWisee Editorial Team
Calculator development and formula review
CalcWisee is an independent site founded by Ayman. Every calculator is built from a published formula or official definition, tested against hand-worked examples before it goes live, and corrected promptly when a reader reports an issue to ayman@calcwisee.com.
Expertise: Financial mathematics, Health and fitness formulas, Applied mathematics, Unit conversion standards
References & sources
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