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Categories: Calculator , Health & Fitness
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Body-fat percentage expresses the proportion of adipose tissue relative to total body mass, while Body-Mass Index (BMI) gauges weight in relation to stature to flag under- or overweight status. Together they outline overall physique health.

This calculator applies the US Navy circumference method to convert neck, waist and, for women, hip girths plus height into an estimated body-fat percentage, then derives BMI and lean- versus fat-mass figures from your chosen metric or imperial units.

Use it to track training progress, set realistic weight-loss targets or verify athletic readiness; *always consult a qualified professional before making medical or nutritional decisions.*

This calculator offers informational estimates, not medical advice.

Technical Details:

The US Navy method links easily measured circumferences to subcutaneous fat concentration, producing a percentage comparable across populations. BMI normalises body weight for height using the square-law relationship of mass to surface area, while lean mass deducts calculated fat mass from total weight.

Core Equations

Males:

BF=86.010×log(W−N)−70.041×log(H)+36.76

Females:

BF=163.205×log(W+Hp−N)−97.684×log(H)−78.387

BMI:

BMI=Weight (kg)Height (m)2
  • H – standing height in centimetres or inches.
  • W – waist circumference at navel level.
  • N – neck circumference just below the larynx.
  • Hp – hip circumference at widest point (female only).
  • BF – body-fat percentage.
CategoryMales %Females %
Essential2–510–13
Athlete6–1314–20
Fitness14–1721–24
Average18–2425–31
Obese25+32+

Lower bands represent vital organ protection, mid-bands align with athletic optimisation, and upper bands correlate with heightened cardiometabolic risk.

Worked example (male, 178 cm, 82 kg, neck = 39 cm, waist = 88 cm):

88−39=49 86.010×log(49)=141.5 70.041×log(178)=116.3 141.5−116.3+36.76=61.9

Estimated body-fat ≈ 19.6 %; BMI ≈ 25.9; lean mass ≈ 66 kg.

Assumptions & Limitations

  • Equations assume adult physiology; accuracy drops for minors.
  • Measurements require relaxed abdomen and normal exhalation.
  • Extremes of muscularity or obesity skew circumference-based estimates.
  • Tool ignores hydration shifts that affect weight and girth.

Edge Cases & Error Sources

  • Zero or negative girth inputs yield invalid logarithms.
  • Height below 100 cm or above 250 cm falls outside validated range.
  • Waist narrower than neck violates equation assumptions.
  • Hip omitted for females returns null results.

Scientific references: Hodgdon & Beckett (1984) Naval Health Research Center report; WHO BMI classification guidelines; Jackson & Pollock skinfold comparison studies.

All calculations run locally; no personal data leaves your device, aiding GDPR compliance.

Step-by-Step Guide:

Follow these actions in sequence for a quick reading.

  1. Select Sex.
  2. Enter Height and choose centimetres or inches.
  3. Provide Weight in kilograms or pounds.
  4. Measure neck and waist circumferences; females also measure hips.
  5. Review the on-screen gauge, composition chart and numeric tables.

FAQ:

How accurate is the calculation?

The circumference method typically falls within ±3–4 percentage points of laboratory measurements for healthy adults.

Can children use this tool?

Formulas were validated on adults; paediatric growth patterns differ, so results for minors may mislead.

Which tape should I use?

A non-stretch tailor’s tape improves repeatability; place it horizontally and level around each landmark.

Is my data stored?

No. Values remain in your browser memory and disappear when you reload or close the page.

Why does BMI differ from body-fat %?

BMI classifies weight for height but ignores composition; muscular physiques may register overweight despite low fat.

Glossary:

Adipose
Body fat tissue.
BMI
Mass-to-height ratio indicating weight status.
Lean Mass
Weight minus calculated fat mass.
Logarithm
Inverse of exponentiation; base-10 here.
Waist-to-Neck
Key ratio in the Navy formula for men.