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Leucine Threshold Calculator

Enter your leucine target and protein source to see how much protein you need per meal.

How it is calculated

The tool divides your leucine target by the share of leucine in the protein: protein needed (g) = leucine target (g) ÷ leucine fraction. The fractions are fixed values per source: whey 11%, egg 8.5%, beef 8.2%, chicken breast 8% and soy 8% of the protein weight. If no source is chosen, whey (11%) is used; a source that is not in the list (pea, casein) gives no result. The answer is grams of protein, not grams of food: a food that is only 20% protein weighs several times more. The result is rounded to a whole gram, and the target must be above zero. Real products vary, so treat the fractions as typical averages.

Worked example

You want 2.5 g of leucine in one meal and your source is soy protein. The tool uses a leucine fraction of 8.00%, so protein needed = 2.5 ÷ 0.08 = 31.25, shown as 31 g of protein. Compare whey at 11%: 2.5 ÷ 0.11 = 22.7, about 23 g. The same leucine dose therefore takes roughly a third more protein from soy than from whey.

Try this example →

Common mistakes

  • Reading the result as grams of food. It is grams of protein, so 31 g of soy protein is a larger weight of soy flour, tofu or a bar, and you must check the label's protein per serving.
  • Forgetting that a blank source means whey. You then get the lowest protein figure (23 g for 2.5 g of leucine), which is too low if you actually eat soy or chicken.
  • Entering the protein dose in the leucine box. The input is the leucine target in grams (typically a few grams), not the meal's protein grams.
  • Looking for a source that is not in the list, for example pea or casein. The tool has only five sources and shows no result for anything else, so pick the closest listed one only if you accept the approximation.
  • Applying one meal's answer to the whole day. The figure is per meal, so a day with four meals needs four such doses.

Sources

About this calculator

The leucine threshold is the amount of the branched-chain amino acid leucine — roughly 2.5 to 3 grams per meal for most healthy adults — needed to maximally trigger muscle protein synthesis (MPS) through activation of the mTOR signaling pathway. Eating protein below this threshold still contributes amino acids, but it does not switch on MPS to the same degree as a dose that clears the threshold.

Research from scientists like Stuart Phillips and Donald Layman established this threshold concept, and it is why nutrition guidance for strength athletes and bodybuilders emphasizes spreading protein evenly across 3-5 meals with enough protein per sitting to clear the leucine threshold, rather than concentrating most daily protein into one or two large meals — a single high-leucine meal cannot 'carry over' its anabolic signal to a later, leucine-poor meal.

This calculator takes your leucine target and uses a typical leucine share for your chosen protein source (whey, egg, chicken breast, beef or soy) to return how many grams of protein from that source you need in one sitting to hit the threshold. The result is grams of protein, not grams of the food itself.

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