Compare Circumference and BMI Fat Estimates
Choose between a Navy circumference equation and a BMI-and-age regression. These methods use different measurements and assumptions, so agreement is not required and neither directly measures body fat.
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- Nothing is uploaded
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How to use this tool
Choose the method before entering values. Circumference mode uses centimetres for height, neck, waist and female hip circumference; BMI mode uses height, weight and age. Keep measurement position consistent.
Results and examples
Read the percentage as an equation estimate. Small tape-measure differences can affect a logarithmic formula, and disagreement with a body-composition test does not establish which result is correct.
Worked example
For a male aged 30 at 70 kg and 170 cm, the BMI regression gives approximately 19.8%.
Limitations
- Original validation populations and detailed measurement protocols still require specialist review.
- The equations do not replace assessment in children, pregnancy or unusual body composition.
Fields
| Field | Guidance and constraints |
|---|---|
| Method | Check the unit and format displayed beside this field. |
| Sex | Check the unit and format displayed beside this field. |
| Height (cm) | Check the unit and format displayed beside this field. |
| Age (BMI method) | Check the unit and format displayed beside this field. |
| Weight (kg, BMI method) | Check the unit and format displayed beside this field. |
| Neck (cm) | Check the unit and format displayed beside this field. |
| Waist (cm) | Check the unit and format displayed beside this field. |
| Hip (cm, female) | Check the unit and format displayed beside this field. |
Data handling
Processing stays in the current browser tab; the site does not upload tool input for the calculation itself.
Frequently asked questions
Which method is the correct one?
Both are estimates; neither establishes your actual body-fat percentage.
Does tape pressure matter?
Yes. Clothing thickness and compressing the tape can change the measurement.
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