- Estimated body fat
- 17.01%
- Estimated fat mass
- 11.91 kg
- Estimated lean mass
- 58.09 kg
How it works
Track measurements before comparing percentages
The male circumference equation uses waist minus neck. If both measurements increase by the same amount while height stays fixed, its percentage stays unchanged. Keep the underlying measurements when tracking results over time.
Comparing body-fat estimation methods
Circumference-based and BMI-based body-fat methods use different measurements, so their results need not agree. Follow the field instructions and use consistent measurement locations and units. Small input changes can affect a percentage estimate. Neither method directly measures all body tissues, and a difference between the two outputs should not be treated as proof that one is an exact measurement.
BMI, age & sex estimate: formula and assumptions
Adult body fat % = 1.20×BMI + 0.23×age − 10.8×maleFlag − 5.4.
Deurenberg’s original study equations estimate body composition statistically. Children use the separate equation 1.51×BMI−0.70×age−3.6×maleFlag+1.4. Results are not measured composition or personal diet targets.
Worked example
Using the Navy circumference estimate example:
- Sex used by the equation
- Male
- Measurement system
- Metric (kg, cm)
- Height (cm)
- 175
- Weight (kg)
- 70
- Waist / abdomen circumference (cm)
- 85
- Neck circumference (cm)
- 38
Male: 86.010 log₁₀(waist−neck) − 70.041 log₁₀(height) + 36.76 (inches).
Example result
Estimated body fat: 17.01%
Estimated fat mass: 11.91 kg
Estimated lean mass: 58.09 kg
These are illustrative inputs. Change the values to explore a different scenario.
Formula references
- US Navy physical readiness resources (opens in a new tab)
- Deurenberg et al. (1991), original study abstract and formulas (opens in a new tab)
References explain the underlying methods; they do not imply endorsement or individual professional review of Finflo.
Common questions
Is circumference-based body fat a direct body-composition measurement?
No. It is an equation-based estimate whose result depends on measurement accuracy and the population assumptions of the method.
Is this the current Army one-site assessment?
No. The historical Navy circumference equations and the Army one-site equation are different models with different inputs.
Does the BMI estimate measure body fat?
No. Deurenberg’s equations combine BMI, age and sex statistically. The adult and child equations are separate, and individual error can be several percentage points.
Prepared by Finflo. See our methodology and editorial policy. Read the relevant professional-advice limitations.