Fitness & Health · Live
Body fat,
from a tape measure.
A precise body-fat percentage calculator using the U.S. Navy circumference method. Enter your height, weight, and a few tape measurements; get your body-fat percentage, fat and lean mass, ACE category, and BMI sanity-check instantly.
Inputs
Body measurements
Tape measurements
Use a soft tape, parallel to the floor, snug but not compressing skin. See the measurement guide below.
- BMI
- 24.5
- BMI category
- Normal
- Lean mass
- 62.2 kg
Body fat
Navy method
Fat mass 12.8 kg · Lean mass 62.2 kg
Fat
17%
Reference
Body-fat percentage scale
| Category | Men | Women |
|---|---|---|
Essential fat | 2 – 5 % | 10 – 13 % |
Athletes | 6 – 13 % | 14 – 20 % |
Fitness | 14 – 17 % | 21 – 24 % |
Average | 18 – 24 % | 25 – 31 % |
Obese | 25 %+ | 32 %+ |
Field guide
How body fat is estimated from a tape measure.
Body fat percentage is the share of your weight that is adipose (fat) tissue, as opposed to muscle, bone, organs, and water, collectively called lean body mass. Unlike BMI, which only uses height and weight, body-fat percentage tells you something about composition: two people of identical BMI can have very different fat-to-lean ratios, and that's the part that matters for most fitness goals.
The U.S. Navy circumference method
Developed by Hodgdon and Beckett in 1984, the Navy method is the most popular tape-only formula. It correlates well — though imperfectly, with hydrostatic weighing for healthy adult populations, and it's free.
Using inches, the formulas are:
Women: %BF = 163.205 · log₁₀(waist + hip − neck) − 97.684 · log₁₀(height) − 78.387
Metric inputs (cm) are converted to inches before the formula is applied. The calculator does this automatically when you toggle units.
How to take the measurements
Accuracy is everything for tape methods — a one-inch error on the waist can shift the result by 2–4 percentage points. Use a soft tape (not a metal one), keep it horizontal and snug but not compressing skin, and breathe naturally.
- Neck: measure just below the larynx, with the tape sloping slightly downward to the front.
- Waist (men): at the level of the navel.
- Waist (women): at the narrowest point of the natural waist, usually just above the navel.
- Hip (women only): at the widest part of the hips/buttocks, with feet together.
- Height: barefoot, against a wall, looking straight ahead.
How accurate is this?
Compared with hydrostatic weighing (the lab gold standard), the Navy method has a typical error of about ±3–4 percentage points for the average person. That's worse than DEXA (about ±2 points) and skinfold calipers in trained hands (about ±2–3 points), but better than BMI alone for assessing composition. The math is also calibrated to healthy adults — it tends to under-estimate body fat for very lean trained athletes and over-estimate it for older sedentary adults.
Body-fat categories
The American Council on Exercise (ACE) categories used in this calculator:
- Essential fat: the minimum needed for basic physiological function. Men 2–5%, women 10–13%.
- Athletes: the typical range for competitive endurance and strength athletes. Men 6–13%, women 14–20%.
- Fitness: visibly lean and active. Men 14–17%, women 21–24%.
- Average: the typical adult range. Men 18–24%, women 25–31%.
- Obese: increased health risk. Men 25%+, women 32%+.
Women carry meaningfully more essential fat than men because of reproductive physiology. That's why every category for women sits ~8 percentage points higher than the equivalent category for men.
Lean body mass and why it matters
Once you have the percentage, computing lean mass is trivial:
leanMass = weight − fatMass
Lean mass is the more meaningful number for setting calorie and protein targets, for example, the Katch–McArdle BMR formula uses lean mass directly, and protein intake recommendations of 0.7–1.0 g/lb are typically stated relative to lean mass, not total body weight.
Worked example
A 175-cm, 75-kg male with a 38-cm neck and 85-cm waist converts to a 68.9 in height, 15.0 in neck, and 33.5 in waist. Plugging in: %BF ≈ 17.0%, which puts him at the Fitness/Average boundary. With 75 kg body weight, that's 12.8 kg fat and 62.2 kg lean mass.
What this calculator doesn't model
The Navy method assumes typical body proportions; very tall or very short individuals, athletes with unusually developed necks (offensive linemen, power lifters), and people with abdominal swelling (illness, ascites) will see larger errors. For training-grade decisions, validate against DEXA every 6–12 months.
Disclaimer
This calculator is an estimate for educational and fitness tracking purposes. It is not a clinical diagnostic tool. Consult a physician before making decisions about weight or body composition, especially if you have a chronic condition.