Lean Body Mass Calculator
Estimate your lean body mass, fat mass and body fat from your weight and height.
How to use the Lean Body Mass Calculator
- Choose metric or US units and select your sex.
- Enter your weight and height.
- Press the Calculate button.
- Read your lean body mass from the Boer, James and Hume formulas and their average.
- Use the fat mass and body fat estimate as a rough guide for tracking progress.
Lean Body Mass Calculator: Estimate Your Lean Mass
Quick answer: lean body mass (LBM) is everything in your body except fat. For most adults it makes up about 60% to 90% of total weight, and men usually have a higher share than women. A lean body mass calculator estimates it from your weight, height and sex.
What Is Lean Body Mass?
Lean body mass is your total body weight minus the weight of your body fat. It counts your muscles, bones, blood, skin, water, tendons, ligaments and internal organs. In other words, it is the part of you that isn’t stored fat.
Doctors use LBM in medicine. The dose of some anaesthetic drugs, especially those that dissolve in water, is based on lean body mass, and some medical tests use LBM values too. For fitness and everyday life, people more often look at body fat percentage, but LBM is useful because it shows how much muscle and other healthy tissue you carry.
Lean Body Mass Formulas for Adults
Several formulas estimate lean body mass from height and weight. In each one, W is your weight in kilograms and H is your height in centimetres. A good calculator shows the results of all of them so you can compare.
Boer formula (1984)
James formula (1976)
Hume formula (1966)
Lean Body Mass Calculator Examples
Example 1: a man
A man weighs 80 kg and is 178 cm tall.
| Formula | Lean body mass |
|---|---|
| Boer | 60.9 kg |
| James | 62.1 kg |
| Hume | 57.1 kg |
| Average of the three | 60.0 kg (about 75% of his weight) |
| Estimated fat mass (80 − 60.0) | 20.0 kg (about 25%) |
Example 2: a woman
A woman weighs 65 kg and is 165 cm tall.
| Formula | Lean body mass |
|---|---|
| Boer | 46.1 kg |
| James | 46.6 kg |
| Hume | 44.9 kg |
| Average of the three | 45.9 kg (about 71% of her weight) |
| Estimated fat mass (65 − 45.9) | 19.1 kg (about 29%) |
The three formulas differ by a few kilograms, which is normal. They are estimates based on averages and cannot see your actual muscle or fat.
Sample results by weight
For a man who is 175 cm tall:
| Weight | Boer | James | Hume |
|---|---|---|---|
| 60 kg | 51.9 kg | 51.0 kg | 49.5 kg |
| 70 kg | 56.0 kg | 56.5 kg | 52.8 kg |
| 80 kg | 60.1 kg | 61.3 kg | 56.1 kg |
| 90 kg | 64.2 kg | 65.1 kg | 59.4 kg |
For a woman who is 165 cm tall:
| Weight | Boer | James | Hume |
|---|---|---|---|
| 50 kg | 42.3 kg | 39.9 kg | 40.5 kg |
| 60 kg | 44.9 kg | 44.6 kg | 43.4 kg |
| 70 kg | 47.4 kg | 48.3 kg | 46.4 kg |
| 80 kg | 49.9 kg | 50.8 kg | 49.4 kg |
Lean Body Mass for Children
The adult formulas are not designed for children. For children aged about 13 to 14 or younger, the Peters formula (2011) is used. It first estimates the volume of fluid outside the body’s cells (extracellular volume, eECV) and then converts it to lean mass:
Example: a child weighs 35 kg and is 140 cm tall. The estimated eECV is about 7.66, so lean body mass is about 3.8 × 7.66 = 29.1 kg, which is roughly 83% of the child’s weight.
Lean Body Mass vs Fat-Free Mass
People often use the two terms as if they mean the same thing, and for most purposes that is fine, but they are slightly different.
- Lean body mass includes muscle, bone, water, tendons, ligaments and internal organs, plus the small amount of essential fat inside organs and tissues.
- Fat-free mass removes all fat, including that essential fat.
The difference between the two is roughly 2% to 3% of body weight in men and 5% to 12% in women, because women carry more essential fat.
Why Lean Body Mass Matters
- Metabolism. Lean tissue uses more energy than fat, so more lean mass generally means a higher resting calorie burn. The Katch-McArdle formula for BMR is based on lean body mass.
- Strength and mobility. Muscle keeps you strong and able to move well, especially as you age.
- Healthy weight loss. A good plan reduces fat while keeping as much lean mass as possible.
- Medical use. Doctors may use LBM to work out some drug doses and test results.
How to Protect or Build Lean Body Mass
- Do strength training two to three times a week.
- Eat enough protein and enough calories overall. Crash diets cost you muscle as well as fat.
- Stay active every day, not only during workouts.
- Sleep seven to nine hours, as sleep supports muscle repair.
- Lose weight gradually if you are trying to lose fat.
Lean Body Mass, Pregnancy and Trying to Conceive
These formulas are not meant for pregnancy. During pregnancy your weight rises because of the baby, the placenta, extra blood and fluid, and your body shape changes, so lean mass estimates would be misleading. Follow your doctor’s advice on healthy weight gain and use our pregnancy calculator to follow your weeks.
If you are planning to conceive, a balanced weight, enough protein and regular gentle exercise help your body prepare. You can check your starting category with our BMI calculator. Avoid crash diets and speak to your doctor before making major changes.
Limitations of Lean Body Mass Formulas
- They use only height, weight and sex, so they cannot tell how muscular you actually are.
- They can be less accurate for very muscular people, very high body weights and older adults.
- Different formulas give different answers for the same person.
- For a precise measurement, a DEXA scan or similar test is more reliable.
Lean Body Mass Calculator FAQs
What is lean body mass?
It is your total weight minus your body fat. It includes muscle, bone, organs, blood, skin and water.
How do I calculate my lean body mass?
Use a formula such as Boer, James or Hume with your weight, height and sex, or enter them into a calculator. If you know your body fat percentage, you can also subtract your fat mass from your weight.
What is a good lean body mass percentage?
It varies, but for most adults lean mass is about 60% to 90% of body weight. Men typically have a higher percentage than women.
Which lean body mass formula is the most accurate?
None is perfect. Comparing the three adult formulas gives you a useful range.
Is lean body mass the same as muscle mass?
No. Lean body mass includes muscle, but also bone, water and organs.
What is the difference between lean body mass and fat-free mass?
Fat-free mass excludes all fat, including essential fat in the organs. Lean body mass includes that essential fat.
Can I use this calculator for a child?
The adult formulas are not for children. For ages 13 to 14 and younger, a formula such as Peters’ is used.
Can I use this calculator during pregnancy?
No. Pregnancy changes your weight and shape, so the results would not be reliable.
How can I increase my lean body mass?
Regular strength training, enough protein and calories, good sleep and patience are the main factors.
Final Thoughts
A lean body mass calculator gives you a quick estimate of how much of your weight is not fat. Use the results as a guide, compare more than one formula and pay attention to trends over time. For a clearer picture, combine them with body fat percentage and your waist measurement, and talk to a doctor if you have any concerns.
Medical disclaimer: This article is for general information and education only. It is not medical advice or a diagnosis. Lean body mass calculators give estimates and may not be accurate for every person.
Please speak to a doctor or registered dietitian before changing your diet or exercise routine, especially if you are pregnant, planning a pregnancy, under 18 or have a medical condition.