Grams to Calories Converter
Convert grams of macronutrients into calories. Enter grams of carbohydrate, protein, fat, and (optionally) alcohol; you get total kcal, the split by macro, kilojoules, and the share of calories coming from fat.
Example: with Carbohydrate (g) 50 · Protein (g) 25 · Fat (g) 15 · Alcohol (g) 0 → Total calories: 435 kcal.
- BreakdownCarbs 200 + protein 100 + fat 135 + alcohol 0 kcal
- In kilojoules1,820 kJ
- Calories from fat31% of total calories
Computed by the calculator below using its default values. Change any input to see your own numbers.
Atwater general factors: 4 kcal/g for carbohydrate and protein, 9 for fat, 7 for alcohol. Every nutrition label is built on them.
Where 4, 4, 9, and 7 come from
Wilbur Atwater burned foods in a calorimeter in the 1890s, then corrected for how much energy humans actually digest and absorb. The general factors that survived — 4 kcal per gram for carbohydrate and protein, 9 for fat, 7 for alcohol — are averages across typical diets, and they are the numbers US labeling regulations still use. Multiply grams by the factor, add up, and you have reconstructed the calorie line on any label.
The factors are deliberately rounded. Specific foods deviate a little (protein from beans digests differently than from eggs), and fiber is the notable special case: though chemically a carbohydrate, insoluble fiber contributes roughly 0 and fermentable soluble fiber about 2 kcal/g, which is why some labels subtract it.
How it’s calculated
Calories = carbs(g) × 4 + protein(g) × 4 + fat(g) × 9 + alcohol(g) × 7 (Atwater general factors, used in US nutrition labeling). Kilojoules = kcal × 4.184. Fat share = fat calories ÷ total × 100.
Atwater factors are diet-wide averages — individual foods vary by a few percent, fiber and sugar alcohols contribute less than the carb factor implies, and label rounding adds its own slack, so totals are estimates rather than lab measurements.
Energy per gram by nutrient
| Nutrient | kcal per gram | 100 g equals |
|---|---|---|
| Carbohydrate | 4 | 400 kcal |
| Protein | 4 | 400 kcal |
| Fat | 9 | 900 kcal |
| Alcohol (ethanol) | 7 | 700 kcal |
| Soluble fiber | about 2 | about 200 kcal |
| Water, minerals | 0 | 0 kcal |
Source: Atwater general factors (USDA); FDA labeling allows about 2 kcal/g for soluble fiber.
Common mistakes
- Multiplying grams of food instead of grams of macronutrient — 100 g of chicken is not 100 g of protein (closer to 31 g).
- Forgetting alcohol: at 7 kcal/g, two beers can out-calorie a dessert while appearing on no macro tracker by default.
- Counting fiber at 4 kcal/g — subtract it (or count about 2 for soluble) when precision matters.
- Mixing up kcal and kJ: food 'calories' are kilocalories; multiply by 4.184 for the kJ figure used on labels abroad.
Frequently asked questions
How do I convert grams to calories?
Multiply grams of each macronutrient by its Atwater factor and add: carbs × 4, protein × 4, fat × 9, alcohol × 7. Example: 50 g carbs + 25 g protein + 15 g fat = 200 + 100 + 135 = 435 kcal.
Why does fat have more calories per gram?
Fat molecules are mostly reduced carbon-hydrogen bonds — dense chemical fuel — while carbs and protein carry more oxygen, which is already 'burned'. Oxidizing fat therefore releases about 2.25 times the energy per gram.
How many calories are in one gram of sugar?
Four, the same as any carbohydrate. A 12 oz soda with 39 g of sugar is 39 × 4 = 156 kcal.
Do these factors work for any food?
As estimates, yes — they are averages across mixed diets and the basis of nutrition labels. Individual foods can differ a few percent in digestibility, and fiber-heavy or sugar-alcohol-heavy foods overstate the most.
Is a calorie on the label the same as a calorie here?
Yes: label calories are computed with these same Atwater factors (kilocalories, technically). Small mismatches you see usually come from rounding rules that let manufacturers round each macro and the total separately.