Adult Fat-Free Mass (Boer) and FFMI Calculator
Estimate adult fat-free mass with the Boer equation and derive FFMI from height using metric or US units.
Content updated: View sources
QuickMedCalc is developed and maintained by an independent developer. Medical content is not independently reviewed by a physician.
Formula and medical content are based on the references listed on this page. See sources, About, and Sources and Review Process.
This page reproduces one historical Boer model after an adult weight, standing height, and published coefficient are entered. It does not determine whether a protocol should use Boer, select a dose, or substitute predicted FFM for a measured body-composition method.
About
Formula
Interpretation
What this equation estimates
Boer is an adult anthropometric regression from body weight, standing height, and a historical published male or female coefficient. The original study used estimated lean body mass for body-fluid-volume normalization; it did not establish universal body-composition diagnostic thresholds.
Worked examples
Male: 70 kg and 175 cm: 0.407 × 70 + 0.267 × 175 − 19.2 = raw estimated FFM 56.015 kg, displayed as 56.0 kg; derived FFMI is approximately 18.3 kg/m².
Female: 60 kg and 165 cm: 0.252 × 60 + 0.473 × 165 − 48.3 = raw estimated FFM 44.865 kg, displayed as 44.9 kg; derived FFMI is approximately 16.5 kg/m². These examples demonstrate arithmetic only and create no normal, low, high, healthy, muscular, sarcopenic, or malnourished category.
FFM, lean mass, and muscle are not interchangeable
In the contemporary two-component chemical model, Boer’s historical LBM concept and FFM are chemically equivalent; modern text uses the chemically correct term fat-free mass. FFM includes water, protein, minerals, bone, and other nonfat components. It is not skeletal muscle mass, appendicular lean mass, contractile muscle, generic lean mass, or DXA lean soft tissue. This calculation is not DXA, BIA, CT, MRI, air-displacement, density, or isotope-dilution measurement.
Derived estimated FFMI
FFMI standardizes estimated FFM by height squared. Reference distributions depend on sex, age, population, and whether FFM was measured or predicted. A cutoff from DXA or BIA research cannot automatically be applied to a Boer-predicted FFMI, so this page assigns no FFMI category and does not diagnose malnutrition, sarcopenia, obesity, or low muscle mass.
Applicability and limits
Age does not enter Boer arithmetic, but this page is for adults. Do not automatically extend it to children, adolescents, pregnancy, edema, ascites, fluid shifts, amputation, or unusual body composition. Repeated estimates can change with weight, fluid, or measurement changes. A drug, contrast, imaging, or research protocol may specify another LBM method; this page does not choose a dose, treatment, or protocol.
References
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol. 1984;247:F632-F636. PMID 6496691.
- VanItallie TB, et al. Height-normalized indices of the body's fat-free mass and fat mass. Am J Clin Nutr. 1990;52:953-959. PMID 2239792.
- Heymsfield SB, et al. Are Lean Body Mass and Fat-Free Mass the Same or Different Body Components? Adv Nutr. 2024;15:100335. PMID 39510253.
- Schutz Y, Kyle UUG, Pichard C. Fat-free mass index and fat mass index percentiles in Caucasians aged 18–98 y. Int J Obes. 2002;26:953-960. PMID 12080449.
- Puri T, Blake GM. Comparison of ten predictive equations for estimating lean body mass with DXA in older patients. Br J Radiol. 2022;95:20210378. PMID 35143259.
- Cederholm T, et al. Diagnostic criteria for malnutrition: an ESPEN Consensus Statement. Clin Nutr. 2015;34:335-340.
- NIST. Guide for the Use of the International System of Units (SP 811): exact conversions, 1 lb = 0.45359237 kg and 1 in = 2.54 cm.
FAQ
It reproduces the adult Boer 1984 regression estimate from body weight, standing height, and a published male or female coefficient, then derives FFMI from the estimated FFM and height.
Boer used the historical term estimated lean body mass. This page uses modern fat-free-mass wording while retaining that historical model identity.
In the contemporary two-component chemical model, the historical LBM concept and FFM are chemically equivalent, and modern terminology favors fat-free mass. Neither term should be confused with DXA lean soft tissue, generic lean mass, appendicular lean mass, skeletal muscle mass, or contractile muscle.
No. Fat-free mass includes water, protein, minerals, bone, and other nonfat components. It is not skeletal muscle, appendicular lean mass, or contractile muscle.
Fat-free mass index divides fat-free mass in kilograms by height in meters squared. Here it is derived from a predicted Boer FFM, not from a direct measurement.
The published Boer regression used historical male and female coefficients. Selecting one reproduces that arithmetic; it is not a direct measurement of body composition or an inference about identity.
No. Age is not an arithmetic input to the Boer formula. Adult applicability and prediction uncertainty still require clinical and population context.
Yes. The page converts US customary inputs using exact 0.45359237 kg per pound and 2.54 cm per inch before applying the kg/cm formula.
No. DXA and bioelectrical impedance are different measurement methods. This calculator is a height-and-weight regression estimate and can differ from instrument-based assessments.
No. FFMI distributions depend on sex, age, population, and whether FFM was measured or predicted. This page intentionally provides no universal FFMI category.
No. A predicted Boer FFMI cannot by itself diagnose sarcopenia, malnutrition, cachexia, obesity, or low muscle mass, and must not be inserted automatically into a clinical framework.
Not automatically. Children, adolescents, pregnancy, fluid shifts, edema, ascites, amputation, and unusual body composition need method- and context-specific assessment.
No. Some protocols specify a particular body-size equation, but this calculator does not select a dosing method, dose, contrast amount, nutrition plan, or treatment.
Use the same units and measurement technique. A change can reflect weight, fluid status, or measurement variation as well as a change in the regression estimate.
Related Calculators
RFM
Estimate adult whole-body fat percentage from height and waist circumference using the published Woolcott–Bergman RFM equation.
BMI
Calculate adult BMI from metric or US customary inputs and view the CDC adult screening category with non-diagnostic interpretation limits.
WHtR
Calculate WHtR from waist circumference and standing height in centimeters or inches, with NICE applicability and measurement limits.
Disclaimer
Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.