Purpose and steps
Uses the U.S. Navy circumference method with height, neck, waist, and female hip measurements. Tape placement and tension materially affect the estimate.
- Choose units and use the pre-pregnancy, resting or current measurements requested by the tool; keep observation dates consistent.
- Prepare Sex used by the equation, Weight, Height, Neck circumference, Waist circumference, Hip circumference. Defaults demonstrate the model rather than your personal circumstances.
- Check the headline result and its components. A key interpretation for this tool is: Use repeated measurements to watch direction rather than relying on one reading.
- Compare the baseline with a changed scenario: Lean mass is the remainder after estimated fat mass is subtracted from body weight.
Input reference and units
These values reproduce the model’s demonstration. Replace them with your own records or measurements; they are not recommended targets.
On a small screen, swipe the table horizontally to see all columns.
| Parameter | Demonstration value | How to enter it |
|---|---|---|
| Sex used by the equation | Female | Use the definition shown in the field label; keep this assumption consistent when comparing scenarios. |
| Weight | 70 kg | Use the definition shown in the field label; keep this assumption consistent when comparing scenarios. |
| Height | 170 cm | Use the definition shown in the field label; keep this assumption consistent when comparing scenarios. |
| Neck circumference | 38 cm | Use the definition shown in the field label; keep this assumption consistent when comparing scenarios. |
| Waist circumference | 82 cm | Use the definition shown in the field label; keep this assumption consistent when comparing scenarios. |
| Hip circumference | 96 cm | Use the definition shown in the field label; keep this assumption consistent when comparing scenarios. |
Model-specific method
How this calculator produces its result
The U.S. Navy circumference equations use logarithms of waist, neck, height, and—when applicable—hip measurements. Estimated fat mass = weight × body-fat percentage.
Logarithms and measurement sensitivity
Circumference models use logarithms to relate combinations of body measurements to a fitted estimate. Logarithms are nonlinear: the effect of a small tape change depends on the existing measurements. A difference inside the logarithm must be positive; invalid geometry cannot be fixed by rounding the output.
Measure at the same locations, tape tension and time when tracking change. A result of 20% to 22% is a two-percentage-point increase, not a 2% relative increase. Circumference estimates do not have the same measurement method or accuracy as imaging-based tests.
log₁₀(ab) = log₁₀(a) + log₁₀(b) For x>0, d(log₁₀x)/dx = 1/(x ln 10) Fat mass = total mass × estimated fat fraction
- log₁₀: base-ten logarithm
- Logarithm input must be strictly positive
- Circumferences must use the units required by the model
- A percentage-point change differs from a percentage change
Worked example
For consistent tracking, measure at the same locations, time of day, and tape tension. A small tape-position change can move the result by several percentage points.
Reproduce the default scenario
This is a separate example, calculated using the exact engine on the tool page and the defaults in the input reference above. Health examples use metric units. Displayed rounding may differ from intermediate precision.
- Estimated body fat
- 27.5%
- Estimated fat mass
- 19.2 kg
- Estimated lean mass
- 50.8 kg
Reading results without overstating them
- Use repeated measurements to watch direction rather than relying on one reading.
- Lean mass is the remainder after estimated fat mass is subtracted from body weight.
Assumptions and exclusions
- Circumference equations are population estimates and can be less accurate for some body shapes.
- They do not replace DEXA or clinician-supervised assessment.
Sources and content notes
Toolify describes the implemented algorithm and its assumptions. Sources below support the topic or applicable rules; they do not endorse this calculator. Examples are illustrative, and published rules take precedence over simplified estimates.
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