Our Method, In Full
Our Method
Our physique calculator uses validated equations from sports science research, ensuring accuracy and reliability for your fitness journey.
- US Navy circumference method (Hodgdon & Beckett, 1984) for body fat percentage when direct measurement isn't available.
- Katch-McArdle formula for Basal Metabolic Rate (BMR) — uses your lean mass rather than total weight alone, which matters most for people who are leaner or more muscular than average.
- FFMI & Normalized FFMI (Kouri et al., 1995) to describe fat-free mass relative to height.
- Customized sport-specific training plans based on trusted, peer-reviewed exercise research.
Research-Based Recommendations
Our recommendations are based on calculations from a specialist doctor, considering ideal body fat, strength-to-weight ratios, and endurance levels for each sport — all designed to help you perform your best and stay healthy.
Calculation Process Flow
Input personal metrics and activity level.
Calculate base metrics (BMI, BMR, body fat %).
Determine sport-specific adjustments and optimal ranges.
Generate personalized recommendations for nutrition and training.
HOW THE FFMI CALCULATION WORKS
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1
Your body fat percentage is used to estimate how much of your body weight is fat versus fat-free tissue.
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2
That fat mass is subtracted from your total body weight, leaving your estimated fat-free mass (also called lean body mass).
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3
Fat-free mass is divided by your height squared (in meters) to calculate your raw FFMI — this puts people of different sizes on a comparable scale, the same idea behind BMI.
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4
A height-adjustment is applied to get the Normalized FFMI, so a 5'6" and a 6'2" person with proportionally similar builds land in a similar range — without it, taller people are structurally penalized.
Lean Body Mass
LBM = Weight × (1 − Body Fat % ÷ 100)
Raw FFMI
FFMI = LBM ÷ Height² (height in meters)
Normalized FFMI
Normalized FFMI = FFMI + 6.1 × (1.80 − Height in meters)
Important accuracy note
Body fat percentage is usually the biggest source of uncertainty in this entire calculation — a tape measurement, a scale, and a DEXA scan can each give a different reading for the same person. Because lean mass, fat mass, and FFMI are all derived from that one number, treat the result as a reasonable estimate rather than an exact measurement, and avoid reading small changes (a point or two) as meaningful — they're often just measurement noise. FFMI is also not a direct measurement of skeletal muscle: fat-free mass includes bone, organs, body water, and connective tissue in addition to muscle.
Methodology & Sources
- Kouri EM, Pope HG Jr, Katz DL, Oliva P. "Fat-free mass index in users and nonusers of anabolic-androgenic steroids." Clinical Journal of Sport Medicine, 1995; 5(4):223-228. — Origin of the FFMI concept and the height-normalization technique used here (the original paper used a normalization constant of 6.3; this calculator uses the commonly-adapted 6.1 variant).
- Hodgdon JA, Beckett MB. "Prediction of Percent Body Fat for U.S. Navy Men and Women from Body Circumferences and Height." Naval Health Research Center, Report No. 84-11, 1984. — Source of the circumference-based body fat formula used when a direct measurement isn't provided.
- McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance. Wolters Kluwer/Lippincott Williams & Wilkins. — Source of the Katch-McArdle BMR equation used for calorie recommendations.
The FFMI reference bands shown on this page (Below Average / Average / Above Average / High) are general descriptive reference points commonly used alongside this formula in fitness and sports-science contexts — they are not a peer-reviewed population percentile table or a medical threshold, and this tool does not attempt to assess how a given physique was achieved.