Lean Mass Index Calculator for Bodybuilding
How to calculate your lean mass index (LMI)?
One of the first indicators when you want to know how fit you are and how healthy you are is to calculate your BMI. (Body Mass Index)It's one of the values we hear most about on television.
Unfortunately, BMI don't do the distinction between body fat and muscle mass. You could therefore be considered obese if you have a crossfitter's physique of 93 kilos for 1.75cm with a bodyfat of 10% (BMI of 30) - admit it, that's a shame!
The lean body mass index (LBMI) is a more accurate measure as it takes into account muscle mass, bones, skin, and other non-fat components of the body
To help you easily calculate your BMI, we have integrated an online calculator on this page
How do I use the IMM calculator?
Using our BMI calculator is simple and quick. Here are the steps to follow:
- Enter your weight in kilograms in the designated field.
- Please enter your height in centimetres.
- Enter your body fat percentage (The methods for determining your body fat percentage are given later in the article, but you can use the image below to estimate your own)..
- Click the button « Calculate » to achieve your IMM.
For example, if you weigh 70 kg, are 175 cm tall, and have 20% body fat, enter these values into the calculator. With just one click, you'll get your BMI and gain a better understanding of your body composition
The main advantage of this online calculator is its accuracy et its ease of use. It allows you to track your progress and adjust your workouts effortlessly. Using this tool, you can get reliable results in seconds, helping you to make informed decisions about your health.
Lean Mass Index Calculator
Your Lean Mass Index
< 18 : Low muscle mass
18-20: Normal muscle mass
20-22: Above average muscle mass
22-23: Excellent muscle mass
> 23 : Exceptional muscle mass
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Interpreting your results: reference values
The Lean Mass Index naturally evolves throughout life. The LMI peaks between the ages of 18 and 30, then gradually decreases with age. This decline accelerates after the age of 60, but your lifestyle choices can influence its extent.
📊 Reference ranges for IMM by age
Hover over the coloured areas to see their interpretation
Detailed reference tables
💡 How to interpret these values:
- IMM Low : May indicate muscle loss (sarcopenia), particularly concerning after the age of 60
- IMM Normal : Healthy muscle mass for your age and gender
- HIGH IMMEDIATE : Developed muscle mass, typical of regular weight training enthusiasts
Learn more about the Calculation methods
To measure your lean body mass index (LBMI), in addition to knowing your height and weight, which are two fairly straightforward values, you will need to calculate your body fat percentage. Here are the main methods to achieve this:
- MRI (Magnetic Resonance Imaging) : This method is highly specific, costly, and generally reserved for medical use
- Skinfold Caliper : better known in the field of bodybuilding and sports in general, this caliper allows you to measure body fat percentage on different parts of the body with varying degrees of accuracy
- Bioelectrical impedance analysis A low electrical current is sent through the body to estimate lean mass and body fat. You can find many scales of this type on the market.
- Estimate image image above
Once the body fat percentage has been determined, here’s how to calculate the BMI:
IMM formula :
IMM = (lean mass in kg / height in m²) + 6.3 × (1.8 – height in m)
Example of calculation :
For a person weighing 70 kg with 20% body fat and measuring 1.75 m:
- Body fat: 70 kg × 0.20 = 14 kg
- Lean mass: 70 kg – 14 kg = 56 kg
- IMM : (56 kg / (1.75 m × 1.75 m)) + 6.3 × (1.8 – 1.75) = 18.29
Comparison between BMI and BMR
L’lean body mass index (LBMI) has a number of advantages over the BMI. Whereas BMI simply relates weight to height, MMI distinguishes between muscle mass and fat mass. This provides a more accurate assessment of body composition.
For example, an athlete with a high muscle mass may have a high BMI, suggesting overweight or obesity, while in reality, their health is optimal. Similarly, a person with low muscle mass but high fat mass may have a normal BMI, thus masking potential health issues. The FFM, by focusing on lean mass, helps to overcome these limitations
BMI
Body Mass Index
❌ Limitations
- Don't differentiate between muscle and fat
- Athletes wrongly classified as "overweight
- Masking sarcopenic obesity
- Simplistic view of health
IMM
Lean Mass Index
✅ Benefits
- Differentiate between muscle and fat
- Accurate assessment for athletes
- Detect sarcopenia (muscle loss)
- Complete health overview
💡 Remember: The IMM provides a much clearer picture of your body composition than the BMI. For weightlifters and athletes, it’s an essential indicator for tracking the progress of your muscle mass
