Lean Mass Index (LMI) Calculator
Calculate fat-free mass per height squared—from body fat or a known fat-free mass.
Two input routes · Metric & US units · Transparent calculations
Your measurements
Your lean mass index
kg/m²
Step-by-step solution
Height-adjusted FFMI
Optional male-study comparison · 1.80 m reference
Uses the 6.3 coefficient reported in the Kouri study abstract. Research comparison, not a personal health category. Applicability to other populations or unusual heights is not established here.
Show the height correction
LMI and BMI tell different stories
Numerical guide—not universal clinical or genetic cutoffs.
Interpret the input, not appearance
Fat-free mass includes more than muscle. Measurement method and body-fat estimation affect the result.
Fat-free mass is more than muscle
What the index includes
Fat-free tissues include muscle, bone, organs and water.
What BMI includes
BMI uses total body weight. LMI uses the fat-free component.
BMI = FFMI + FMI, when the components use the same total weight and height.
Calculation & assumptions
Choose the right input route
From body fat: FFM = weight × (1 − body-fat % / 100). Direct route: enter known fat-free mass, including bone.
Keep mass definitions consistent
DXA lean soft tissue alone excludes bone mineral and is not interchangeable with total fat-free mass.
Optional height normalization
The research comparison is separate from raw LMI. This page uses 6.3 as reported in Kouri's abstract; the original research involved male athletes.
Rounding & units
Height and mass are stored in SI units; display conversions do not replace those stored quantities. The chart labels are rounded; the equation holds before rounding.
Input scope
Height 50–300 cm and weight 0.5–1,000 kg are broad software checks, not clinical reference ranges. Known FFM must be positive and no greater than total body weight.
Frequently asked questions
Is LMI the same as FFMI here?
This calculator defines the index as total fat-free mass divided by height squared. With this mass definition the raw LMI shown here is FFMI. Check the definition when comparing with other tools.
Which input route should I choose?
Choose From body-fat percentage if you know total weight, height and a body-fat estimate. Choose From known fat-free mass if you have an FFM value that includes bone mineral. Body weight is used to check the mass and to calculate BMI and FMI.
Does fat-free mass mean muscle mass?
No. It is the nonfat component of the model and includes more than skeletal muscle. DXA lean soft tissue alone excludes bone mineral and should not be entered as total FFM.
Why does the adjusted value differ?
The optional male-study comparison adds 6.3 × (1.80 − height in metres) to raw FFMI, using the coefficient reported in the Kouri study abstract. Raw LMI is always shown separately.
Is there a universal genetic limit?
This calculator does not classify an index as a genetic limit or infer substance use. A value observed in a particular research sample is not a universal personal ceiling.
Why can measurement methods disagree?
The mass compartment, body-fat estimation method, height measurement and rounding can differ. Compare results only when the definitions and methods are compatible.
More questions (9)
What does the Lean Mass Index (LMI) calculate?
It calculates total fat-free mass in kilograms divided by height in metres squared. From body fat, FFM = weight × (1 − percentage / 100).
Which values should I enter?
Enter your body weight and height with the selected units, then a body-fat percentage or known total fat-free mass. The initial 75 kg, 175 cm and 20% are sample inputs.
What formula does this calculator use?
FFM = W × (1 − p / 100); LMI = FFM / h². Direct FFM input uses LMI = entered FFM / h². BMI = W / h² and FMI = (W − FFM) / h².
Why might my result differ from another source?
Check the units, mass definition, input method, body-fat estimate and whether the other result is raw or height-adjusted. Different normalization coefficients also give different adjusted values.
Does the result update automatically?
Yes. Inputs recalculate the index, mass split, graphs and formula substitutions. Invalid inputs clear previous results and diagrams.
Can everyone use the height correction?
It is an optional research comparison based on a study of male athletes, not a universal biological correction. Its applicability to other populations or unusual heights is not established here.
Why does BMI equal FFMI plus FMI?
Both components are divided by the same height squared. Their masses add up to the same total body weight, so their indices add up to BMI before rounding.
Does switching units change the result?
No. Height and mass are stored internally in centimetres and kilograms. Switching only changes the display units; ratios are calculated from the stored quantities.
What are the input checks?
Height accepts 50–300 cm and body weight 0.5–1,000 kg as broad software limits, not validated clinical ranges. Body fat must be at least 0 and below 100%; known FFM must be positive and no greater than total weight.
Sources & References
References provide context, not endorsement. No institutional certification or expert review of this page is claimed.
Page information
Updated: October 26, 2026
Educational calculation. Discuss personal body-composition results with a qualified healthcare professional.