How many calories are in a gram of protein, carbs and fat?
The four numbers
These are the standard Atwater factors [1]:
| Nutrient | kcal per gram |
|---|---|
| Protein | 4 |
| Carbohydrate | 4 |
| Fat | 9 |
| Alcohol | 7 |
Worked example
A snack bar has 10 g protein, 20 g carbs and 5 g fat:
- Protein: 10 × 4 = 40 kcal
- Carbs: 20 × 4 = 80 kcal
- Fat: 5 × 9 = 45 kcal
- Total: 165 kcal
Why fat matters most for calories
Gram for gram, fat has more than twice the calories of protein or carbs. A tablespoon of oil or butter adds up fast. That is why cooking fat is the item people most often forget to log.
How much protein do adults need?
The US Recommended Dietary Allowance for adults is 0.8 g of protein per kg of body weight a day [2]. A 70 kg adult needs about 56 g. That is a minimum, not a target for athletes.
What "macro split" means
A macro split is the share of your calories from protein, carbs and fat. A balanced split might be 30% protein, 40% carbs and 30% fat. A keto split puts most calories in fat and very few in carbs.
Quick answers
How many calories are in 1 gram of fat?
About 9 kcal. Protein and carbohydrate have about 4 kcal per gram, and alcohol about 7.
How do I calculate calories from macros?
Multiply grams of protein by 4, grams of carbs by 4 and grams of fat by 9, then add them up.
How much protein do I need a day?
The US RDA for adults is 0.8 g per kg of body weight a day. That is a minimum, not an upper limit.
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Get Plate-wise freeSources
- FAO. Food energy: methods of analysis and conversion factors, chapter 3. www.fao.org
- Is it time to reconsider the U.S. recommendations for dietary protein and amino acid intake? (NIH PubMed Central) pmc.ncbi.nlm.nih.gov
General information, not medical advice. Talk to a doctor or registered dietitian about your own needs.