This lean body mass calculator gives you an instant estimate of your fat-free mass — the combined weight of your muscles, bones, organs, and body water — using just your height, weight, and sex. No body fat percentage measurement required, no calipers, no expensive DEXA scan.
Whether you're tracking your fitness progress, setting your protein intake, or simply curious about what your weight is actually made of, lean body mass gives you a far more useful picture of your health than the scale number alone.
Enter your details above and get your result in seconds.
What Is Lean Body Mass?
Lean body mass (LBM) is the total weight of your body minus all fat tissue. It includes:
- Skeletal muscle — the tissue you build through training
- Bones — your structural framework
- Organs — liver, kidneys, heart, brain, and everything else
- Body water — intracellular and extracellular fluid
- Connective tissue and skin
Despite the name, lean body mass doesn't mean muscle mass alone — though muscle is a major component. Think of it as your fat-free mass: the metabolically active tissue that drives your strength, energy expenditure, and physical function.
Here's the simple equation:
Total Body Weight = Lean Body Mass + Fat Mass
So if you weigh 180 lbs and carry 30 lbs of fat, your lean body mass is 150 lbs.
That split matters more than most people realize. Two people can weigh exactly the same and look completely different — one carrying mostly lean tissue, the other carrying significantly more fat. Lean body mass tells you which side of that equation you're on.
How to Use This Calculator
Using this lean body mass calculator takes about 30 seconds:
- Select your sex — Choose male or female. Sex affects the calculation because men and women have different typical distributions of muscle, fat, and bone density.
- Enter your weight — Type in your current body weight and select your preferred unit (pounds or kilograms).
- Enter your height — Input your height and choose feet or centimeters.
- Read your result — Your lean body mass appears instantly in your preferred unit.
That's it. No body fat percentage needed, no complicated measurements. The calculator uses a validated formula to estimate your LBM from just these three inputs.
Understanding Your Lean Body Mass Results
Once you have your number, here's how to interpret it.
LBM as a Percentage of Total Weight
The most useful way to read your result is as a percentage of your total body weight:
Category | Men (% LBM) | Women (% LBM) |
|---|---|---|
Athletic | 85–90%+ | 78–85%+ |
Fit | 80–84% | 73–77% |
Average | 75–79% | 68–72% |
Below Average | Below 75% | Below 68% |
To calculate: divide your LBM by your total weight and multiply by 100.
Example: LBM of 140 lbs ÷ total weight of 175 lbs × 100 = 80% LBM — solidly in the "fit" range for a man.
Keep in mind these are general guidelines. Age, training history, frame size, and genetics all influence what's realistic and healthy for you personally.
The Formula Behind the Calculation
This calculator uses the Boer formula, one of the most widely cited and validated methods for estimating lean body mass from basic measurements:
For Men: LBM = (0.407 × weight in kg) + (0.267 × height in cm) − 19.2
For Women: LBM = (0.252 × weight in kg) + (0.473 × height in cm) − 48.3
Worked example — Male, 80 kg, 178 cm: LBM = (0.407 × 80) + (0.267 × 178) − 19.2 = 32.56 + 47.53 − 19.2 = 60.89 kg
Worked example — Female, 65 kg, 165 cm: LBM = (0.252 × 65) + (0.473 × 165) − 48.3 = 16.38 + 78.05 − 48.3 = 46.13 kg
The Boer formula was developed and validated specifically using height, weight, and sex as inputs — making it ideal for a calculator that doesn't require a body fat percentage measurement.
Why Lean Body Mass Matters
Most people track total weight. But total weight is just one number — and it doesn't tell you much on its own. Lean body mass gives you real insight into what's actually happening in your body.
For Fitness and Muscle Building
LBM is the go-to metric for tracking body composition progress. When you're strength training and gaining weight, the real question is: is that extra weight muscle, or fat? Tracking your LBM over time answers that clearly.
If your total weight rises but your LBM stays flat, you're gaining mostly fat. If your LBM climbs while total weight barely moves, you're genuinely changing your body composition — muscle gain alongside fat loss.
For Weight Loss
When you're cutting calories to lose fat, you want to preserve as much lean mass as possible. Losing weight too aggressively — crash dieting, very low calories — tends to sacrifice muscle alongside fat. Monitoring your LBM helps you see whether your approach is actually protecting your muscle tissue.
For Metabolism
Lean body mass is the primary driver of your resting metabolic rate — the calories your body burns at rest. More LBM means a higher baseline metabolism. That's why two people of identical weight can have meaningfully different calorie needs.
For Medical Context
Healthcare providers use lean body mass to calculate medication dosages (particularly for drugs that don't distribute into fat tissue), assess nutritional status, and monitor patients with conditions like kidney disease, sarcopenia, or cancer. In those contexts, LBM provides a more accurate baseline than total body weight alone.
Lean Body Mass and Protein Intake
One of the most practical uses of your LBM result is setting your protein target.
The evidence-based recommendation for active people is 1.6–2.2 grams of protein per kilogram of lean body mass per day — and some research supports going toward the higher end during intense training blocks.
Goal | Protein per kg LBM |
|---|---|
Maintain muscle while dieting | 2.0–2.4 g/kg |
Build muscle (regular training) | 1.6–2.0 g/kg |
Athletic performance | 1.8–2.2 g/kg |
General health maintenance | 1.2–1.6 g/kg |
Example: If your LBM is 60 kg and you're training to build muscle, aim for 96–120 grams of protein per day (60 × 1.6–2.0).
Using LBM rather than total body weight for protein calculations is more accurate — it avoids inflating targets for people carrying more fat mass.
Practical Examples
Example 1: Male, 185 lbs (83.9 kg), 5'11" (180 cm)
LBM = (0.407 × 83.9) + (0.267 × 180) − 19.2 = 34.15 + 48.06 − 19.2 = 63.0 kg (138.9 lbs)
At 185 lbs total, this person carries about 46.1 lbs of fat — a body fat percentage of roughly 24.9%, in the average-to-fit range. If he's training regularly, protein target: ~101–126 grams per day.
Example 2: Female, 140 lbs (63.5 kg), 5'5" (165 cm)
LBM = (0.252 × 63.5) + (0.473 × 165) − 48.3 = 16.0 + 78.0 − 48.3 = 45.7 kg (100.7 lbs)
At 140 lbs, she has 100.7 lbs of lean mass — a body fat of around 28%, well within the healthy range for women. For muscle building, protein target: ~73–91 grams per day.
Example 3: Male, 220 lbs (99.8 kg), 6'2" (188 cm)
LBM = (0.407 × 99.8) + (0.267 × 188) − 19.2 = 40.62 + 50.2 − 19.2 = 71.6 kg (157.8 lbs)
Despite weighing 220 lbs, his lean mass is 157.8 lbs — roughly 28.3% body fat. Tracking LBM monthly while strength training and dialing in nutrition will show whether he's genuinely shifting body composition over time.
How to Improve Your Lean Body Mass
The good news is that lean body mass responds well to consistent, evidence-based habits — and even modest improvements make a meaningful difference.
1. Strength Train Consistently Progressive resistance training is the most effective stimulus for building and preserving muscle. Three to four sessions per week, with gradual increases in weight or reps over time, produces reliable LBM gains.
2. Hit Your Protein Target Protein provides the raw material for muscle repair and growth. Without adequate protein, even excellent training produces limited results. Calculate your target using your LBM as shown above, and distribute intake across meals throughout the day.
3. Eat at the Right Calorie Level To build LBM, you generally need a small caloric surplus — around 200–300 calories above maintenance. To lose fat while protecting lean mass, a moderate deficit of 10–20% below maintenance works better than aggressive restriction.
4. Prioritize Sleep Muscle protein synthesis happens primarily during sleep. Consistently getting 7–9 hours isn't just a wellness recommendation — it's a direct input into whether your training actually translates to LBM gains.
5. Track Trends, Not Single Data Points Lean body mass changes slowly. Month-over-month tracking gives you the trend that matters; week-to-week measurements can swing significantly based on hydration and other variables. Be patient — meaningful body composition shifts happen over months.
Technical Notes
Formula: Boer Formula (1984)
- Men: LBM = (0.407 × weight in kg) + (0.267 × height in cm) − 19.2
- Women: LBM = (0.252 × weight in kg) + (0.473 × height in cm) − 48.3
Limitations: This calculator provides population-level estimates. Results may vary based on body frame, hydration level, training history, age, and other individual factors. The formula was validated on general adult populations and may be less accurate at extreme body weights or heights.
Disclaimer: This tool is for informational and educational purposes only. It does not constitute medical advice. Consult a qualified healthcare provider for personalized guidance on body composition, health goals, or any medical concerns.