Why body-fat equations need consistent units: centimetres are not inches
A circumference equation contains logarithms and fitted constants. Mixing units cannot be repaired by converting the final percentage.
Body fat calculator →Compare equivalent measurements
A height of 180 cm is about 70.866 inches, a 90 cm waist is about 35.433 inches and a 40 cm neck is about 15.748 inches. Entering corresponding metric or imperial measurements should produce the same estimate, apart from rounding introduced when the measurements are shortened. Changing units changes the representation, not the body being measured.
The logarithmic formula is not a simple ratio
The male equation is 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76, using inches internally. Substituting raw centimetre values into those constants changes the result. Multiplying the resulting percentage by 2.54 afterward cannot repair that substitution. The calculator converts length inputs before applying the equation.
Keep a complete unit convention
Use one measurement system consistently within a record, including kilograms or pounds for weight. Avoid repeatedly rounding converted values before re-entering them. The equation does not automatically adjust its body-fat percentage for age and is not a precise measurement for every population. The conversion tool can check measurements, while BMI offers a separate calculation with different limitations.
Try the calculators
- Body fat calculator
Estimate body fat from height and circumferences in metric or imperial units.
- Unit converter
Convert length, mass, area, volume, speed and data size.
- BMI calculator
Calculate body mass index from height and weight.