Body metrics and body fat

The calculator needs age, the sex category used by the equations, height and weight. Age must be an integer of at least 18; height and weight must be positive. Metric entries use cm and kg, while imperial entries use ft/in and lb. The service normalises imperial measurements with 1 in = 2.54 cm and 1 lb = 0.45359237 kg before most equations run.

Available estimates are RFM, Deurenberg, Hodgdon-Beckett and a manually entered body-fat value. Comparison values appear only when their required measurements were entered, and the tool does not average them. Fat mass, fat-free mass, FFMI and Katch-McArdle use only the valid selected estimate.

RFM, Deurenberg and Hodgdon-Beckett are equation estimates, not direct measurements. A manual value is merely reused as supplied; its quality depends on the external measurement.

RFM uses height and waist in the same length unit and the formula sex category; the project documents it as an adult estimate for the studied US population. A positive waist is required.

Deurenberg uses BMI, age and formula sex. BMI is calculated from kg and metres only as an intermediate value: this tool provides neither BMI classification nor Real-BMI categories.

For Hodgdon-Beckett the service converts all measurements to inches before logarithms. MALE needs positive waist/abdomen and neck values; FEMALE also needs a positive hip value and all logarithm arguments must be positive. These historical anthropometric equations are not presented as a current military fitness test.

An estimate at or outside 0–100% is marked outside the estimation range and produces no fat mass, FFM, FFMI or Katch-McArdle result. A positive waist separately enables WHtR. FFM is not muscle mass: it also includes water, bone and organs. The tool assigns no risk light, universal category or diagnosis to WHtR or FFMI.

For age 30, MALE, 180 cm, 80 kg and a 90 cm waist with RFM selected, the service calculates RFM = 64 − 20 × 180 / 90 = 24%. That is the selected estimate, not a measurement.

It then returns 19.2 kg fat mass, 60.8 kg FFM, FFMI = 60.8 / 1.8² = 18.765432… kg/m² and WHtR = 90 / 180 = 0.5. Display formatting uses at most two decimals for body fat, fat mass and FFM and three for FFMI and WHtR; there is no intermediate rounding.

W is kg, H is cm and A is years. Mifflin-St Jeor and Revised Harris-Benedict use the basic inputs; Katch-McArdle appears only with valid FFM and identifies whether that FFM is estimated or manual. All are estimated kcal/day, not total energy needs, PAL or calorie targets.

Devine uses 50 kg (MALE) or 45.5 kg (FEMALE) plus 2.3 kg per inch above 60 in; Robinson uses 52/49 kg plus 1.9/1.7 kg. Both return no value below 152.4 cm. Lemmens is sex-neutral. These are equation-based references, not personal target weights or health advice.

For age 30, FEMALE, 165 cm, 65 kg, waist 75 cm, neck 32 cm and hip 98 cm with Hodgdon-Beckett selected, the service first converts lengths to 64.960629…, 29.527559…, 12.598425… and 38.582677… inches. The female equation returns BF% = 29.23849372767515…%.

It derives 19.005020922988848… kg fat mass and 45.99497907701115… kg FFM; the page displays 29.24%, 19.01 kg and 45.99 kg. The other estimates are neither averaged nor used as corrections.

No model is shown as a gold standard. Missing measurements create no substitutes; invalid logarithm domains block Hodgdon-Beckett, and Devine/Robinson are not extrapolated below their documented height range. The page formats only at the end: at most two decimals for body fat, fat mass, FFM, BMI and reference weights; three for FFMI and WHtR; whole kcal/day for resting energy.

The calculator performs no direct body-fat measurement, indirect calorimetry or medical assessment. It contains no diagnosis, treatment, nutrition or weight-loss recommendation. An equation estimate cannot replace measured body composition or individually measured resting energy.