Ketogenic Ratio Calculator (4:1 and 3:1 Classic Keto Diet)
Plan a classic ketogenic diet by ratio (4:1, 3:1, 2:1 or 1:1): turn daily calories and protein into grams of fat, protein and net carbs using dietary units.
How it works
kcal per dietary unit = 9 × R + 4 · dietary units = daily kcal ÷ (9R + 4) · fat (g) = R × units · protein + net carbs (g) = units · carbs = units − protein
The classic ketogenic diet used for drug-resistant epilepsy is prescribed as a weight ratio of fat to protein-plus-carbohydrate. A 4:1 dietary unit is 4 g fat + 1 g protein/carbohydrate = 36 + 4 = 40 kcal, giving about 90% of energy from fat; a 3:1 unit is 31 kcal (87% fat). Dividing the calorie prescription by the energy of one unit gives the number of units, and the protein requirement is subtracted from the non-fat grams to leave the carbohydrate allowance. Lower ratios such as 2:1 or 1:1 resemble the modified Atkins and low-glycaemic-index diets.
Worked example
1,500 kcal at a 4:1 ratio with 30 g protein: one unit = 9 × 4 + 4 = 40 kcal, so 1,500 ÷ 40 = 37.5 units. Fat = 4 × 37.5 = 150.0 g; protein + carbs = 37.5 g, so net carbs = 37.5 − 30 = 7.5 g. Fat supplies 90.0% of calories.
Sources: Kossoff EH et al. (2018) Optimal clinical management of children receiving dietary therapies for epilepsy: updated recommendations of the International Ketogenic Diet Study Group. Epilepsia Open 3:175–192 · Charlie Foundation — Classic ketogenic diet
Frequently asked questions
What does a 4:1 ketogenic ratio mean?
For every 4 g of fat you eat 1 g of protein plus carbohydrate combined. It is the strictest standard medical ketogenic diet, with about 90% of calories from fat.
How much protein can I have on a 4:1 diet?
Protein and carbs share the non-fat grams, so the more protein, the less carbohydrate. Children on medical keto diets usually get at least the protein recommended for age (around 1 g/kg); the calculator tells you when the protein target is too high for the ratio.
Is the ketogenic ratio the same as keto macros?
No. Weight-loss keto plans set percentages, often 70–75% fat, which is about a 1.5:1–2:1 ratio. The classic therapeutic diet at 3:1–4:1 is much stricter and should be supervised by a medical team.
Are net carbs or total carbs used?
Most epilepsy centres count net carbohydrate (total minus fibre) in the ratio, and fibre is still encouraged. Follow the method used by your keto team, because it changes the numbers slightly.
Related calculators
This calculator is for education only. A therapeutic ketogenic diet must be started and monitored by a doctor and dietitian, because it can cause low blood sugar, acidosis, kidney stones and growth or nutrient problems.