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Body Fat Percentage Calculator

Estimate your body fat percentage with the U.S. Navy method using simple tape-measure inputs. See your category, lean body mass, and fat mass instantly.

Body fat inputs

This calculator is for informational purposes only and is not a substitute for professional medical advice. Consult a qualified healthcare provider before making changes to your diet, exercise, or health regimen.

What is body fat percentage and why does it matter?

Body fat percentage (BF%) is the fraction of your total body mass that consists of fat tissue. Unlike BMI it distinguishes muscle from fat, which makes it a much more useful number for anyone who trains seriously or who wants a picture of body composition rather than just total weight. Two people at the same height and weight can have BF% figures that differ by 15 percentage points — one might be lean and athletic, the other might carry a lot of stored fat around the middle.

Body fat matters for health as well as appearance. Very low body fat disrupts hormones, immune function, and reproduction. Very high body fat — especially visceral fat stored around abdominal organs — is strongly associated with cardiovascular disease, type 2 diabetes, and metabolic syndrome. Knowing roughly where you sit on the spectrum helps you set realistic goals and notice meaningful change over time.

How this calculator works

We use the U.S. Navy method, a circumference-based formula developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 and calibrated against hydrostatic underwater weighing. It needs only a tape measure and a few body landmarks. The equations take inputs in inches; our calculator handles unit conversion automatically.

  • Men: BF% = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
  • Women: BF% = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387

Once BF% is known, we compute fat mass (body weight × BF%/100) and lean body mass (body weight − fat mass) and classify the result against the American Council on Exercise body-fat categories, which differ for men and women.

Worked example

Consider a man who is 180 cm tall, weighs 82 kg, with a neck circumference of 38 cm and a waist of 86 cm. Converting to inches: height 70.87, neck 14.96, waist 33.86. Waist − neck = 18.90.

  • 86.010 × log₁₀(18.90) = 86.010 × 1.2765 ≈ 109.80
  • 70.041 × log₁₀(70.87) = 70.041 × 1.8505 ≈ 129.61
  • BF% = 109.80 − 129.61 + 36.76 ≈ 16.95% — call it 17.0%
  • Fat mass = 82 × 0.17 ≈ 13.9 kg
  • Lean body mass = 82 − 13.9 ≈ 68.1 kg

The ACE "Fitness" category for men is 14–17%, so this individual sits right at the edge of that band. A small reduction in waist measurement would move him into the 14–17% fitness bracket; a small increase would push him into the 18–24% average range.

How to take good measurements

The Navy formula is extremely sensitive to the quality of your tape readings. A centimetre of measurement error on the waist can shift the final BF% by a full percentage point. Use these practices:

  • Use a flexible, non-stretch cloth or fibreglass tape.
  • Measure on bare skin, not over clothing.
  • Keep the tape horizontal and snug but not compressing the skin.
  • Relax — don't flex, suck in, or brace.
  • Take each measurement twice and re-measure if the two readings differ by more than 1 cm.
  • Measure at the same time each day, ideally in the morning before eating.

How to interpret the result

Body fat percentages are classified differently for men and women because of inherent physiological differences in essential fat. The ACE categories are:

  • Essential fat: men 2–5%, women 10–13% (minimum for health)
  • Athletes: men 6–13%, women 14–20%
  • Fitness: men 14–17%, women 21–24%
  • Average: men 18–24%, women 25–31%
  • Obese: men 25%+, women 32%+

For most people the sustainable sweet spot is the top of the "Athletes" band or the middle of "Fitness": lean enough to look and feel good, loose enough to train hard and recover well, sustainable indefinitely without constant dieting. Going lower is possible but requires ongoing effort and, below essential-fat levels, carries real health costs.

Common mistakes

  • Measuring waist in the wrong place. Men: at the navel. Women: at the narrowest point.
  • Sucking in. Breathe normally and relax. Tape should lie flat without compressing.
  • Measuring over clothes. Bare skin only. Even a T-shirt adds several millimetres.
  • Comparing a single measurement to a target. Circumferences fluctuate 1–2 cm day to day. Use a rolling average of several measurements over 2–3 weeks.
  • Treating the number as gospel. It is an estimate with a ±3–4% error band. Use it to track change, not as an absolute truth.

When to consult a professional

If your body fat percentage seems implausibly high or low, if you are training for a weight-class sport, if you are recovering from or at risk of an eating disorder, or if you have a medical reason to know body composition precisely, seek out a professional measurement. Sports medicine clinics, university labs, and some hospitals offer DEXA scans, hydrostatic weighing, and air-displacement plethysmography (Bod Pod) — all of which are considerably more accurate than any tape-based estimate.

Frequently Asked Questions

What is the U.S. Navy body fat method?
The U.S. Navy method is a body-composition estimate developed by Hodgdon and Beckett at the Naval Health Research Center in 1984. It predicts body fat percentage from a small number of body circumferences — height, neck, waist, and (for women) hip — and was calibrated against hydrostatic underwater weighing. The Navy still uses it for fitness screening. It is free, needs only a tape measure, and typically falls within 3–4% of hydrostatic weighing for most adults.
How accurate is it really?
On average, the Navy method is within ±3–4 percentage points of laboratory methods for most adults of typical build. It gets less accurate at extremes — very lean athletes and very obese people — and it can be thrown off by unusual body proportions (wide hips, narrow waist, thick neck). It is far more accurate than visual estimation and comparable to a mid-range bioimpedance scale, but less precise than a DEXA scan or hydrostatic weighing.
How do I measure my waist, neck, and hip correctly?
Use a flexible non-stretch tape. Neck: just below the larynx, tape horizontal, not pulled tight. Waist (men): at the navel, relaxed, not sucked in. Waist (women): at the narrowest point, usually slightly above the navel. Hip (women only): at the widest part of the buttocks. Stand naturally, breathe normally, and take each measurement twice — if the two readings differ by more than 1 cm, do a third.
Why is the formula different for men and women?
Men and women have different fat-distribution patterns. Men tend to store more fat in the abdominal region, while women store proportionally more fat around the hips and thighs. Hodgdon and Beckett derived two separate regression equations — one using waist and neck for men, another adding hip circumference for women — to reflect those patterns. Using the wrong formula for your sex will produce a meaningless number.
What is a healthy body fat percentage?
Men: essential fat 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, obese 25%+. Women: essential fat 10–13%, athletes 14–20%, fitness 21–24%, average 25–31%, obese 32%+. These ranges come from the American Council on Exercise. Women require a higher essential-fat minimum because of reproductive and hormonal function. Going below essential fat levels for sustained periods is medically dangerous for either sex.
Is lower body fat always better?
No. Contest-level bodybuilders diet down to 3–5% body fat briefly before stepping on stage, but holding that level is neither healthy nor sustainable — hormonal function drops, immune function suffers, mood deteriorates, and sleep breaks down. For men, the 10–15% range is a realistic sustainable "lean and healthy" target; for women, 18–22% is the analogous band. Below those ranges you are trading health for appearance.
How is lean body mass calculated?
Lean body mass is simply your body weight minus your fat mass. If you weigh 80 kg and measure at 15% body fat, your fat mass is 80 × 0.15 = 12 kg and your lean body mass is 80 − 12 = 68 kg. Lean body mass includes muscle, bone, organs, connective tissue, and the water inside them. It is the number you want to preserve during weight loss.
Why did my result clamp at 2% or 60%?
Extreme measurements (a waist-to-neck ratio near 1, an unusually tall or short height) can push the logarithmic formula outside the human range. We clamp results to a physiologically plausible 2–60% band. If you hit the clamp, double-check your tape measurements — especially whether you confused inches with centimetres or measured in the wrong location.
How often should I measure?
Once every 2–4 weeks is enough for most people. Body fat percentage changes slowly, and daily fluctuations from hydration, digestion, and salt intake can swing circumference readings by a centimetre or two, which translates into 1–2 percentage points of noise. Always measure at the same time of day under the same conditions — ideally in the morning, after using the bathroom, before eating or drinking.
Should I rely on this for medical decisions?
No. This calculator is a general-purpose screening tool, not a medical measurement. If a clinician needs to evaluate your body composition to guide treatment they will order a DEXA scan, hydrostatic weighing, or air-displacement plethysmography. Use this number to track your own progress over time; do not use it to diagnose or medicate.