Macro Calculator — FAQ
What are macronutrients?
Macronutrients (macros) are the three main nutrients that provide calories in food: protein, carbohydrates, and fat. According to the USDA’s Atwater system:
- Protein: 4 calories per gram
- Carbohydrates: 4 calories per gram
- Fat: 9 calories per gram
How does this calculator work?
This calculator converts calories to grams using the Atwater general factor system, the standard method used by the USDA and FDA for nutrition labeling. You enter your calorie target and percentage split, and it calculates the corresponding gram amounts.
Formulas:
- Protein (g) = (Calories × Protein%) ÷ 4
- Carbs (g) = (Calories × Carbs%) ÷ 4
- Fat (g) = (Calories × Fat%) ÷ 9
What is the Atwater system?
The Atwater system, developed by Wilbur Atwater in the 1890s, establishes the caloric values of macronutrients. These values (4-4-9 for protein, carbs, and fat respectively) are used universally in nutrition labeling and dietary calculations.
What macro splits are commonly referenced?
Various macro splits are referenced in nutrition and fitness communities:
| Type | Protein | Carbs | Fat |
|---|---|---|---|
| Balanced | 30% | 40% | 30% |
| Higher Protein | 40% | 30% | 30% |
| Higher Carb | 30% | 50% | 20% |
| Low Carb | 40% | 20% | 40% |
| Very Low Carb (Keto) | 20% | 5% | 75% |
The appropriate split varies by individual. Consult a registered dietitian for personalized guidance.
Why do my percentages need to add up to 100%?
Since protein, carbs, and fat are the only macronutrients that provide calories, their percentages must total 100% to account for your entire calorie intake. If they don’t sum to 100%, the gram calculations won’t match your calorie target.
Why do fat grams seem lower than protein or carb grams?
Fat contains 9 calories per gram, while protein and carbs contain only 4 calories per gram. This means the same percentage of calories from fat produces fewer grams than from protein or carbs.
Example at 2000 calories:
- 30% from protein = 600 cal ÷ 4 = 150g
- 30% from fat = 600 cal ÷ 9 = 67g
What is IIFYM?
IIFYM stands for “If It Fits Your Macros,” a flexible approach to nutrition tracking where people aim to meet daily macro targets rather than following specific meal plans. This calculator can help estimate those targets.
How many calories per gram of protein?
According to the Atwater system used by the USDA and FDA, 1 gram of protein = 4 calories. This is why the calculator divides protein calories by 4 to get grams.
How many calories per gram of fat?
According to the Atwater system, 1 gram of fat = 9 calories. Fat is more calorie-dense than protein or carbs, which is why the calculator divides fat calories by 9.
How many calories per gram of carbohydrates?
According to the Atwater system, 1 gram of carbohydrate = 4 calories, the same as protein.
Are these results personalized dietary advice?
No. This calculator performs mathematical conversions only. It does not account for individual factors such as age, sex, health conditions, activity level, or dietary needs. The results are estimates based on the percentages you enter. For personalized nutrition advice, consult a registered dietitian or healthcare provider.
Where do the caloric values come from?
The 4-4-9 caloric values are established by:
- USDA (United States Department of Agriculture)
- FDA (Food and Drug Administration) for nutrition labeling
- Original research by Wilbur Atwater (1896)
These values are the standard used in nutrition science and food labeling worldwide.