Use this free lean body mass calculator to estimate how much of your body weight is lean mass and how much is fat. Enter your height, weight, and sex above to get results in seconds. The calculator applies proven formulas (Boer and Hume) so you can understand your body composition without a lab visit.
Your lean body mass (LBM) is everything in your body that is not fat. That includes muscle, bone, organs, water, and connective tissue. Knowing your LBM helps you set smarter fitness goals, personalize calorie targets, and track progress beyond the number on a scale.
Calculate your lean body mass
To calculate your lean body mass, enter three inputs into the calculator above:
- Sex (male or female): the formulas use sex-specific coefficients
- Height: in centimeters or inches
- Body weight: in kilograms or pounds
The calculator then applies two validated estimation formulas and returns your estimated lean body mass and body fat percentage. No blood work. No body fat calculator gadget. Just height and weight.
Results appear instantly. Use them as a starting benchmark for meal planning, training programming, or a conversation with a coach or dietitian.
What is lean body mass?
Lean body mass is your total body weight minus your fat mass. It represents the weight of everything in your body that is not stored fat.
LBM includes:
- Skeletal muscle
- Bones
- Organs (heart, liver, kidneys, brain)
- Blood and water
- Tendons, ligaments, and other connective tissue
- Essential fat (a small amount your body needs to function)
Because lean body mass includes so many tissues, it is not the same as "muscle mass." It is a broader measure of your body composition.
Body weight vs. muscle mass and body fat
Your total body weight is the sum of lean body mass and fat mass. Two people can weigh the same yet look very different because one carries more muscle and less fat.
This is why the scale alone tells an incomplete story. A lean body mass calculator separates your weight into these two buckets so you can see whether changes come from gaining muscle, losing fat, or both.
Skeletal muscle, bone, and lean body mass
Skeletal muscle is the muscle you can train. It is the largest single component of lean body mass, but not the only one.
Bone density, organ weight, and water also contribute. So your skeletal muscle mass will always be lower than your total lean body mass. This distinction matters when comparing numbers across different calculators or DEXA scans.
If someone asks "how do lean body mass and skeletal muscle mass differ," the short answer is scope. LBM includes skeletal muscle plus everything else that is not fat.
How the LBM calculator uses your body weight to estimate body composition
This online calculator relies on empirical formulas developed from population studies. Researchers measured lean body mass in hundreds of people using precise lab methods, then built equations that predict LBM from easy inputs: height, weight, and sex.
The formulas work by estimating fat mass first, then subtracting it from total body weight. Because they use sex-specific coefficients, results account for the average differences in body composition between males and females.
No formula is perfect. These equations were built from averages. They perform best for people in a typical body fat range and may be less accurate for very muscular individuals or people with very high body fat.
Lean body mass formula and equation
The calculator applies two well-known formulas so you can compare results. Both estimate lean body mass from height and weight alone, no body fat percentage needed.
The Boer formula
The Boer formula (1984) is one of the most commonly cited lean body mass equations.
For males: LBM = (0.407 × weight in kg) + (0.267 × height in cm) − 19.2
For females: LBM = (0.252 × weight in kg) + (0.473 × height in cm) − 48.3
This formula tends to perform well across a broad range of body types and is a reliable general estimation.
The Hume equation
The Hume equation (1966) uses a similar approach with slightly different coefficients.
For males: LBM = (0.32810 × weight in kg) + (0.33929 × height in cm) − 29.5336
For females: LBM = (0.29569 × weight in kg) + (0.41813 × height in cm) − 43.2933
Why do formulas give different results? Each was derived from a different study population and measurement method. Small differences in the final number are expected. Neither is "wrong." Comparing the two gives you a reasonable range for your lean body mass.
Body fat percentage and how it relates to lean body mass
Body fat percentage is the flip side of lean body mass. If your LBM is 75% of your total body weight, your body fat percentage is roughly 25%.
The relationship is simple:
- Body fat percentage = (fat mass ÷ total body weight) × 100
- Lean body mass percentage = 100 − body fat percentage
General reference ranges (these vary by age and source):
| Category | Males | Females |
|---|---|---|
| Athletes | 6–13% body fat | 14–20% body fat |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Above average | 25%+ | 32%+ |
A lean body mass of around 75–85% of total body weight is typical for males with moderate fitness. For females, 65–75% is common due to naturally higher essential fat. These are rough ranges, not clinical cutoffs.
Is 75% lean body mass good? For most people, yes, that falls within a healthy zone. But "good" depends on your age, sex, activity level, and personal goals. Consult a healthcare provider for individualized guidance.
LBM, body composition, and the weight calculator
A standard weight calculator tells you total body weight. A BMI calculator compares weight to height. Neither tells you what your weight is made of.
This lean body mass calculator adds that missing layer. It separates your weight into lean mass and fat mass so you can:
- Set realistic calorie targets based on lean mass (since muscle tissue drives your basal metabolic rate)
- Understand whether weight gain reflects muscle growth or fat gain
- Make more informed decisions about training volume and nutrition
Think of LBM as the foundation for other calculations. Many TDEE and calorie calculators produce better results when you input lean body mass instead of just total body weight. The more you know about your overall body composition, the better you can personalize your plan.
Tracking your progress with the lean body mass calculator
Weigh-ins alone can mislead you. If you gain 2 kg of muscle and lose 2 kg of fat, the scale reads the same. An LBM estimate reveals the shift underneath.
Tips for tracking progress:
- Measure at the same time of day. Morning, after using the bathroom, before eating, gives the most consistent readings.
- Use the same units every time. Stick to kilograms and centimeters, or pounds and inches. Mixing units introduces error.
- Log results weekly or biweekly. Day-to-day weight fluctuations are mostly water. Trends over weeks show real changes.
- Compare formula outputs over time. The absolute number matters less than the direction. If both Boer and Hume show lean mass trending up, your training is likely working.
- Pair with other measures. Progress photos, strength benchmarks, and how clothes fit all add context the formula cannot capture.
This calculator is a free, quick way to track progress without expensive DEXA scans or body fat calipers.
Estimate, not a precise measure: what this LBM calculator cannot do
This LBM calculator provides an estimation, not a clinical measurement. Keep these limitations in mind:
- It cannot replace DEXA scans, hydrostatic weighing, or other lab methods. Those tools measure body composition directly. Formulas predict it from population averages.
- It may be less accurate for muscular individuals. If you carry significantly more muscle than average, the formulas may underestimate your lean body mass.
- It does not account for age, ethnicity, or fitness level. The Boer and Hume formulas use only height, weight, and sex.
- It is not medical advice. Do not use these results to diagnose a condition or replace guidance from a healthcare provider. Consult a qualified professional for clinical decisions.
Use the results as a planning aid and directional guide. They are helpful for setting fitness goals and monitoring trends, not for making medical judgments.
Frequently asked questions
How do I calculate lean body mass without body fat percentage?
The Boer and Hume formulas estimate lean body mass using only height, weight, and sex. No body fat percentage input is needed. The calculator on this page applies both formulas automatically.
If you do know your body fat percentage, you can also calculate LBM manually:
LBM = total body weight × (1 − body fat percentage as a decimal)
For example, a person weighing 80 kg with 20% body fat: 80 × (1 − 0.20) = 64 kg lean body mass.
What is a healthy LBM for my body weight?
There is no single "healthy" number. Lean body mass depends on sex, height, age, and activity level.
As a rough guide, many healthy males carry 75–85% of total body weight as lean mass. For females, 65–75% is common. An LBM around 79% of body weight, for example, is generally within a normal range for an active male.
These are estimates. A healthcare provider or registered dietitian can give you a personalized target.
How is this calculator different from a BMI or calorie calculator?
A BMI calculator divides your weight by height squared. It cannot tell you how much of that weight is muscle versus fat. A calorie calculator estimates energy needs.
This lean body mass calculator estimates the composition of your weight. It tells you how much is lean tissue and how much is fat. That information can then improve the accuracy of a calorie or TDEE calculator.
Can I use this LBM calculator in kilograms and centimeters?
Yes. The calculator accepts both metric (kg and cm) and imperial (lbs and inches) inputs. The underlying Boer and Hume formulas use metric units. If you enter imperial units, the calculator converts them before running the equation.
How does skeletal muscle mass differ from lean body mass?
Skeletal muscle mass is one component of lean body mass. LBM includes skeletal muscle plus bones, organs, water, connective tissue (tendons, ligaments), and essential fat.
Your skeletal muscle mass will always be a smaller number than your total lean body mass. If a DEXA scan or gym device reports "skeletal muscle mass," do not compare it directly to the LBM figure from this calculator. They measure different things.