Lean Body Mass Calculator
Estimate your lean body mass with the Boer and James formulas, from your weight, height and sex.
What Lean Body Mass Is and Why It Matters
Lean body mass is your weight without the fat. It is the muscle, bone, organs, connective tissue and water that make up the rest of you. Some people call it fat-free mass. Your body fat and your lean mass add up to your full body weight.
The number matters because muscle drives strength, supports your joints and burns more energy at rest than fat does. Two people can weigh the same and look very different, because one carries more lean mass and less fat. Knowing your lean mass gives you a clearer picture than the scale on its own.
The Boer and James Formulas
This calculator uses two well-known equations. The Boer formula and the James formula both estimate lean body mass from your weight, height and sex. Each one weighs those inputs a little differently, so the tool shows both results and the average of the two.
Take a man at 80 kg and 180 cm. The Boer formula returns 61.4 kg of lean mass. The James formula returns 62.7 kg. The average comes out to about 62.1 kg, which puts his lean mass in the range of 61 to 63 kg and his body fat near 22 percent.
Lean Mass Versus Body Fat
Your body fat and your lean mass are two sides of the same total. Raise one and the other falls as a share of your weight. To see your fat side of the picture, run the body fat calculator. To check where your weight sits against your height, use the BMI calculator.
BMI alone cannot tell muscle from fat, so a muscular person can read as overweight while carrying little fat. Pairing BMI with lean mass and body fat gives a fuller read. To see a healthy weight range for your height, try the ideal weight calculator.
How to Build and Keep Lean Mass
Two habits build and protect lean mass: strength training and eating enough protein. Lift or do resistance work a few times a week, and give your muscles the raw material to repair and grow. To set a daily protein target that supports your lean mass, use the protein calculator.
Tracking helps you see if the plan is working. The Velpa app logs your weight and steps in one private place, so you can watch the trend over weeks instead of guessing from a single reading. This page is general information, not medical advice. For a precise body composition number, ask a clinic about a DEXA or similar scan.
Frequently asked questions
- What is lean body mass?
- Lean body mass is your total weight minus your fat. It includes muscle, bone, organs, connective tissue and the water in your body. It is sometimes called fat-free mass. A man who weighs 80 kg at 180 cm carries about 61 to 63 kg of lean mass, with the rest being body fat.
- How is lean body mass calculated?
- This tool uses two validated equations, Boer and James, that estimate lean mass from your weight, height and sex. It shows each result and the average of the two. For a man at 80 kg and 180 cm the Boer formula gives 61.4 kg, the James formula gives 62.7 kg, and the average is 62.1 kg.
- What is the difference between lean body mass and body fat?
- Body fat is the fat your body stores. Lean body mass is everything else. The two add up to your full body weight. If you weigh 80 kg with 18 kg of fat, your lean body mass is 62 kg. Tracking both tells you more than the scale alone, because two people at the same weight can have very different amounts of muscle and fat.
- Is a higher lean body mass better?
- More lean mass usually means more muscle, which supports strength, metabolism and healthy ageing. The goal is not endless gain but enough muscle for your body and your activity. Strength training and enough protein build and protect lean mass over time.
- How accurate is this lean body mass estimate?
- The Boer and James formulas give a solid estimate for most adults from height and weight alone. They do not measure your body, so they cannot match a DEXA, hydrostatic weighing or a body scan. Use the number to track trends, not as a clinical reading. This is general information, not medical advice.