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This FFMI calculator is designed to estimate your fat-free mass index, a more precise measure than BMI (body mass index), especially for well-trained individuals and athletes. In this article, you’ll find an explanation of FFMI, a comparison between BMI and FFMI, and an FFMI scale for classification.

For an accurate calculation, you’ll need your body fat percentage, which can be obtained using a body fat calculator. If you’re interested in alternative body fat measurements, explore our US Navy body fat calculator.

FFMI – Fat-Free Mass Index

FFMI, or fat-free mass index, quantifies your muscle mass relative to height and weight. While less commonly used than BMI, FFMI provides more accurate information about an individual’s condition and health.

FFMI incorporates three inputs for muscle mass scoring:

  1. Body height: Measured in centimeters or feet and inches.
  2. Body weight: Measured in kilograms or pounds.
  3. Body fat: Measured in percentage units (use our body fat calculator to find this value).

BMI vs. FFMI

BMI relies on weight and height, lacking consideration for lean muscle mass and body fat. This limitation leads to inaccuracies, especially for athletes with varying muscle mass. FFMI, however, distinguishes between fat and muscle gain, making it a superior choice for those with higher muscle mass.

Why is FFMI Better than BMI?

BMI might classify both fat and muscle gain as weight increase, but FFMI differentiates between the two. An increase in fat decreases FFMI, while an increase in muscle raises it. For those with higher muscle mass, like athletes, FFMI is a more effective measure compared to BMI.

FFMI Interpretation

The following tables classify FFMI scores for men and women:

FFMI Range for Men

  • Below 18: Below average
  • 18-20: Average
  • 20-22: Above average
  • 22-23: Excellent
  • 23-26: Superior
  • 26-28: Suspicion of steroid use
  • More than 28: Steroid usage likely

FFMI Range for Women

  • Below 15: Below average
  • 15-17: Average
  • 17-18: Above average
  • 18-19: Excellent
  • 19-21.5: Superior
  • 21.5-25: Suspicion of steroid use
  • More than 25: Steroid usage likely

Note: FFMI scores between 26-27.9 for men may indicate steroid use, and scores between 28-30 are highly unlikely without steroids.

How to Calculate FFMI

The FFMI calculator uses approved formulas:

  1. Body fat calculation: body fat = weight [kg] × (body fat [%] / 100)
  2. Fat-free mass estimation: fat-free mass = weight [kg] × (1 - (body fat [%]/ 100))
  3. FFMI calculation: FFMI = fat-free mass [kg]/ (height [m])²
  4. Normalized FFMI: normalized FFMI = FFMI [kg/m²] + 6.1 × (1.8 - height [m])

Units can be adjusted in the calculator.

How to Use the FFMI Calculator

Let’s illustrate with an example for clarity. Consider Steve, 180 cm tall, 75 kg weight, and 22% body fat:

  1. Enter height: 180 cm
  2. Enter weight: 75 kg
  3. Enter body fat: 22%

Outcome:

  • FFMI: 18.1 kg/m² (average)
  • Normalized FFMI: 18.1 kg/m² (no height adjustment)
  • Steve’s fat-free mass: 58.5 kg
  • Steve’s total body fat: 16.5 kg

FAQ

How to calculate FFMI?

Use the equations provided in the article.

What is a healthy fat-free mass index?

For men, average FFMI is 18-20; for women, 14-17. Athletes may have higher values.

How to lower body fat without losing muscle mass?

Maintain a balanced diet, do cardio and weight training, and be patient.

Examples of fat-free mass?

Inner organs, bones, ligaments, tendons, connective tissue, muscles, blood, and nerves.