One of the first indicators when you want to know your physical fitness and health is to calculate your BMI (Body Mass Index), which is one of the most mentioned values in television shows. Unfortunately, the BMI does not distinguish between fat mass and muscle mass. You could be considered obese if you have a crossfitter physique of 93 kilos for 1.75 cm with a body fat of 10% (BMI of 30), admit it’s quite unfortunate!
The Lean Mass Index (LMI) 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 calculate your LMI easily, we have integrated an online calculator on this page
How to use the LMI calculator?
Using our LMI calculator is simple and quick. Here are the steps to follow:
- Enter your weight in kilograms in the designated field.
- Indicate your height in centimeters.
- Enter your body fat percentage (we provide methods to know your body fat percentage further down in the article, but you can use the image below to estimate yours).
- Click the “Calculate” button to get your LMI.
For example, if you weigh 70 kg, measure 175 cm, and have 20% body fat, enter these values into the calculator. With one click, you will get your LMI and can better understand your body composition.
The main advantage of this online calculator is its accuracy and ease of use. It allows you to track your progress and adjust your workouts effortlessly. By using this tool, you can obtain reliable results in seconds, helping you make informed decisions for your health.
Lean Mass Index Calculator
Your Lean Mass Index
- < 18: Low muscle mass
- 18-20: Normal muscle mass
- 20-22: Above average
- 22-23: Excellent muscle mass
- > 23: Exceptional muscle mass
Our other calculators
We have created many calculators to help you optimize your loads, such as our one-rep max calculator, but also for your nutrition with our basal metabolic rate calculator, as well as a daily whey protein quantity calculator. If you liked this calculator, you will surely like those too
📊 IMM reference zones by age
Hover over the colored areas to see their interpretation
Detailed reference tables
| IMM reference values - Men | |||
|---|---|---|---|
| Age range | Low IMM | Normal IMM | High IMM |
| 18-39 years | < 18.5 | 18.5 - 20.5 | > 20.5 |
| 40-59 years | < 18.0 | 18.0 - 20.0 | > 20.0 |
| 60-79 years | < 17.5 | 17.5 - 19.5 | > 19.5 |
💡 How to interpret these values:
- Low IMM: May indicate muscle mass loss (sarcopenia), particularly concerning after 60 years
- Normal IMM: Healthy muscle mass for your age and gender
- High IMM: Developed muscle mass, typical of regular weight training practitioners
Learn more about Calculation methods
To measure your Lean Mass Index (LMI), in addition to knowing your height and weight, which are two fairly easy values, you will need to calculate your body fat percentage. Here are the main methods to achieve this:
- MRI (Magnetic Resonance Imaging): Very accurate, this method is costly and generally reserved for medical use.
- Skinfold calipers: more known in the field of bodybuilding and sports in general, this caliper allows measuring the fat rate on different parts of the body with more or less precision.
- Bioelectrical impedance analysis: A low electrical current is sent through the body to estimate lean mass and fat mass. Many scales of this type are available on the market.
- Estimation image: the image provided above
Once the body fat percentage is determined, here is how to calculate the LMI:
LMI Formula:
LMI = (lean mass in kg / height in m²) + 6.3 × (1.8 – height in m)
Calculation example:
For a person weighing 70 kg with 20% body fat and measuring 1.75 m:
- Fat mass: 70 kg × 0.20 = 14 kg
- Lean mass: 70 kg – 14 kg = 56 kg
- LMI: (56 kg / (1.75 m × 1.75 m)) + 6.3 × (1.8 – 1.75) = 18.29
Comparison between LBM and BMI
The Lean Body Mass (LBM) index has several advantages over BMI. While BMI simply relates weight to height, LBM distinguishes between muscle mass and fat mass. This allows for a more accurate assessment of body composition.
For example, an athlete with high muscle mass may have a high BMI, suggesting overweight or obesity, when 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. LBM, by focusing on non-fat mass, overcomes these limitations.
BMI
Body Mass Index
Limitations
- Does not differentiate muscle and fat
- Athletes wrongly classified as "overweight"
- Masks sarcopenic obesity
- Simplistic view of health
LBM
Lean Body Mass Index
Advantages
- Distinguishes muscle and fat
- Accurate assessment for athletes
- Detects sarcopenia (muscle loss)
- Comprehensive view of health
