Estimated body fat

31.6258

Computed from default inputs using graph `synth-body-fat-calculator`.

Waist

90 cm

Range: 30 - 250

This estimate uses the US Navy circumference method — developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 — which predicts body fat from tape measurements alone: waist, neck, and height for men; waist, hip, neck, and height for women, computed here in centimeters with the sex-branched logarithmic equations.

Solve for Height

Height: 163.1777 for Estimated body fat 34.793

US Navy tape-measure body fat estimate in metric units (cm), sex-branched.

bodyFatPercent=\max\left(0,\min\left(70,\left(\begin{cases} {\frac{495}{\left(1.0324-0.19077\cdot\log_{10}\left(\max\left(1, waistCm- neckCm\right)\right)+0.15456\cdot\log_{10}\left( heightCm\right)\right)}}, &\quad{\text{if }\; isMale=1}\\{\frac{495}{\left(1.29579-0.35004\cdot\log_{10}\left(\max\left(1, waistCm+ hipCm- neckCm\right)\right)+0.221\cdot\log_{10}\left( heightCm\right)\right)}}, &\quad{\text{otherwise}}\end{cases}\right)-450\right)\right)

bodyFatPercentmax(0, min(70, (isMale == 1 ? 495 / (1.0324 - 0.19077 * log10(max(1, waistCm - neckCm)) + 0.15456 * log10(heightCm)) : 495 / (1.29579 - 0.35004 * log10(max(1, waistCm + hipCm - neckCm)) + 0.22100 * log10(heightCm))) - 450))

Estimated body fat decision comparison

item	value	note
Stress low	69.61	Height: 80
Conservative	44.92	Height: 131.25
Downside	36.41	Height: 157.5
Base case	31.63	Height: 175
Upside	27.38	Height: 192.50000000000003

Visual Analysis1 series8 points

Expanded chart built from the same sensitivity run as the table, so users can read the trend and verify the numbers in one place.

Trend

Downward

Min

28.3814

Max

69.6085

Insight

Estimated body fat shows a downward pattern, with a visible peak around 80 at 69.6085.

Visual response curve for Estimated body fat.

Tracking a cut with the tape, not the scale
A man at 178 cm holding steady at 84 kg for a month reads waist 88 → 84 cm and neck steady at 39 cm across four weekly measurements. The scale says nothing happened; the tape-method estimate drops about 2.5 percentage points — body recomposition the scale is blind to. This is the use case where the Navy method shines: same tape, same landmarks, same time of day, trend over weeks.

How accurate is the tape method against a DEXA scan?
Validation studies place the standard error around 3–4 % body fat for typical adults — worse than DEXA or hydrostatic weighing, better than most consumer impedance scales, and dramatically better than visual guessing. The military still uses it operationally, paired with defined measurement protocols, because consistency of technique keeps the error stable.

Why do the male and female equations use different measurements?
Fat distribution differs by sex: the male equation captures central fat with waist minus neck, while the female equation adds the hip measurement because gluteofemoral fat is a substantial and metabolically distinct store the waist alone misses. Using the wrong branch produces results wrong by 8–10 points, not subtly off.

What ranges count as healthy?
Commonly cited fitness references put essential fat near 3–5 % for men and 10–13 % for women, athletic ranges around 6–13 % and 14–20 %, and acceptable ranges extending to roughly 24 % and 31 % respectively. These are conventions rather than clinical cutoffs; trend direction under a consistent protocol carries more information than position against any chart.

Health tools disclaimer: Educational estimates only, not medical advice, diagnosis, or treatment. For clinical decisions, dosing, or emergencies, follow guidance from US Department of Health & Human Services and a licensed professional in your jurisdiction.

Estimate body fat percentage from tape measurements using a Navy-style metric equation.

Body Fat Calculator turns Waist, Neck, Height, Hip, and Sex (1 = male, 0 = female) into Estimated body fat. Confirm the units and assumptions match your situation before relying on the result.

Check you can supply every input the formula needs. The US Navy method needs waist, neck, and height for men, and adds hip circumference for women. Use it only if you can measure all of them — a missing input is filled by an assumption you cannot see.
Measure at a consistent time of day. Take measurements first thing in the morning, before eating or drinking. Waist circumference moves by a centimetre or more across a normal day, which is larger than most week-to-week change.
Place the tape at the standard landmarks. Waist at the navel for men and at the narrowest point for women; neck just below the larynx, sloping slightly downward at the front; hip at the widest point. Keep the tape level and snug without compressing the skin.
Repeat each measurement. Take each circumference three times and use the middle value. Tape placement, not the equation, is the dominant source of error — a single centimetre at the waist moves the estimate about 0.7 percentage points.
Read the result as a range, not a number. Compare the figure against the ACE category ranges for your sex and treat it as carrying several percentage points of uncertainty. A trend across weeks is meaningful; a single reading to one decimal place is not.

Overwhelm from technical jargon

Start with the basic inputs only — advanced options can be explored once you understand the fundamentals. Important: Don't be discouraged if your results seem unfavorable — these tools help you plan, not judge.

Enter your values, then check the formula, scenarios, and FAQ to confirm the assumptions fit your case. For medical, financial, legal, or safety-critical decisions, treat the output as an estimate and verify it against the relevant professional standard.

World Health Organization. "Body mass index - BMI." WHO Regional Office for Europe, 2024.BMI classification thresholds: underweight <18.5, normal 18.5-24.9, overweight 25-29.9, obese ≥30
Centers for Disease Control and Prevention. "About Child & Teen BMI." CDC, 2024.Pediatric BMI uses age-sex-specific percentiles, not adult thresholds
Mifflin MD, St Jeor ST, et al. "A new predictive equation for resting energy expenditure in healthy individuals." Am J Clin Nutr. 1990;51(2):241-247.BMR formula: 10×weight(kg) + 6.25×height(cm) - 5×age - 161 (female) or +5 (male)
Institute of Medicine. "Weight Gain During Pregnancy: Reexamining the Guidelines." National Academies Press, 2009.Recommended pregnancy weight gain by pre-pregnancy BMI category

When is this health estimation context enough?
Use it when the result only depends on age, sex, height and no local rule changes the interpretation.

What should I record with the result?
Record the input values, reference population, measurement unit, activity estimate, output unit, and rounding rule used in the calculation.

When should I use a specialized modifier?
Use a specialized modifier when measurement units, reference range, age/sex context, and non-diagnostic limits materially changes how the same result should be explained.

Measuring at the wrong landmarks. The protocol is specific: waist at the navel for men (narrowest point for women), neck just below the larynx, hip at the widest point. Moving the waist tape a few centimeters changes the estimate by multiple percentage points — most "my body fat jumped overnight" reports are landmark drift.

Pulling the tape tight.

Body Fat Calculator

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