How this calculator works
General Atwater factors convert an adult daily energy split to grams: carbohydrate and protein supply about 4 kcal/g and fat about 9 kcal/g. Each input share must be 10 to 70% and the shares must sum to 100%. The output flags splits outside adult Acceptable Macronutrient Distribution Ranges. It does not assess micronutrients, food quality or individual dietary needs. The result is an estimate for information only and is not medical advice.
Formula
Carbohydrate grams = kcal x carbohydrate fraction / 4; protein grams = kcal x protein fraction / 4; fat grams = kcal x fat fraction / 9.
Worked example
At 2500 kcal with a 50/20/30 split, the unrounded values are 312.5 g carbohydrate, 125 g protein and 83.3 g fat.
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Frequently asked questions
Why must the shares sum to 100%?
The split allocates all the entered daily energy among three macronutrients.
Is a low carbohydrate split always invalid?
No. The tool accepts it within the input bounds, but flags values outside the general adult distribution ranges.
Why are carbohydrate and protein divided by 4 and fat by 9?
Those are general Atwater factors: carbohydrate and protein supply about 4 kcal/g and fat about 9 kcal/g.