I remember when I started tracking protein… and aimed my target at my total bodyweight while carrying a bit of a belly. Eighty-five kilos on the scale, so I ate for 85 kilos. Months later, when I finally measured my body fat properly, I realised a good chunk of that weight was not muscle at all — and I had been overeating protein for tissue that does not need it. Fat does not need feeding. Muscle does.
In this article
The Lean Body Mass Protein Calculator above fixes the target. Enter your weight and your body fat percentage. It splits you into lean mass and fat mass, then gives you a protein range based on the part of you that actually uses it: 1.6 to 2.2 grams per kilo of lean mass, with a midpoint recommendation.
Why lean mass is the honest denominator
Bodyweight is a rough proxy. Two people can both weigh 90 kilos: one is a lean lifter at 12% body fat, the other is sedentary at 32%. The lifter has about 79 kilos of lean mass; the other has about 61. Feeding both of them for 90 kilos makes no sense — one gets too little, the other wastes money on excess.
| Person | Weight | Body fat | Lean mass | Protein target (1.9× lean) |
|---|---|---|---|---|
| Lean lifter | 90 kg | 12% | 79.2 kg | 150 g |
| Average active | 90 kg | 22% | 70.2 kg | 133 g |
| Higher body fat | 90 kg | 32% | 61.2 kg | 116 g |
Same scale weight, three different answers, 34 grams apart. That gap is a full meal. The British Nutrition Foundation explains body composition in plain terms if you want the background.
The lean-mass protein formula
First split the weight, then multiply the lean part. With W as weight in kilos and b as body fat percentage:
| Variable | What it is | Example |
|---|---|---|
| W | Bodyweight in kilos | 75 kg |
| b | Body fat percentage | 20% |
| Lean mass | Everything that is not fat | 60 kg |
| 1.6–2.2 | Evidence-based factor range | midpoint 1.9 |
Be honest about the body fat number — most people underestimate it. A cheap set of calipers, a bioimpedance scale used consistently, or even a visual comparison chart all beat a guess. The NHS Eat Well guide keeps the official line sensibly moderate on all of this.
A worked example: 75 kilos at 20% body fat
Let me walk you through my exact setup for the most common case I see — an active adult, 75 kg, roughly 20% body fat, wants to build a bit of muscle.
| Step | Calculation | Result |
|---|---|---|
| Lean mass | 75 × (1 − 0.20) | 60.0 kg |
| Fat mass | 75 − 60 | 15.0 kg |
| Low end | 60 × 1.6 | 96 g |
| High end | 60 × 2.2 | 132 g |
| Midpoint | 60 × 1.9 | 114 g |
Compare that with the bodyweight method: 75 × 1.8 = 135 g. The lean-mass method says 96–132 g. For this person the difference is modest, but at higher body fat the gap becomes a whole meal — and that is where this calculator earns its keep.
Using the Lean Body Mass Protein Calculator step by step
Enter your two numbers at the top of this page, then press Calculate.
| Input field | What to enter | Sample figure |
|---|---|---|
| Weight (kg) | Your current scale weight | 75 |
| Body fat (%) | Measured, not guessed | 20 |
You get your lean mass and fat mass in kilos, the protein target range (1.6–2.2 g per kg of lean mass) and a midpoint recommendation. Everything runs in your browser. For the simpler bodyweight version, the Protein Intake Calculator on the home page does it in one step; to split the resulting target across your day, use the Protein Per Meal Planner; and to see the calories around it, the TDEE Calorie Calculator.
When lean-mass targeting matters most
When dieting from a higher body fat. This is the big one. A 100-kilo person at 35% body fat has 65 kilos of lean mass — feeding them for 100 kilos is overkill by a third.
When you are already lean and bulking. At 12% body fat the two methods nearly agree, which is reassuring — it means the simple method was fine all along.
When the number feels impossible. If your bodyweight target seems unreachable, check the lean-mass version. You may discover you were aiming 30 grams too high, and the realistic target is one you will actually hit.
Questions I get asked about lean mass and protein
Should I base protein on lean mass or total weight?
For most people, total weight is fine and simpler — the difference is small at average body fat. I switch to lean mass when someone is above about 25% body fat (men) or 32% (women), because that is where the bodyweight method starts overshooting meaningfully. Below that, do whichever you will actually stick with.
How do I measure body fat percentage at home?
Honestly, cheaply and consistently rather than accurately. A bioimpedance scale used at the same time of day tracks trends well even if the absolute number is off. Calipers are better in trained hands. I avoid the mirror-guess — everyone, including me, underestimates by about 5%.
Does fat mass need any protein?
Essentially no — adipose tissue has minimal protein turnover compared with muscle. That is the whole logic of this calculator. Your organs and muscles need the amino acids; your fat stores do not. This is also why very lean people need the high end of the range and dieters at higher body fat can use the lower end.
What if I do not know my body fat percentage?
Then use the home-page Protein Intake Calculator, which works from total bodyweight — it is the right tool when you lack the measurement. Do not guess a body fat number to force this calculator to work; a guessed input just gives you a confident-sounding wrong answer.
