Body Fat Calculator
Estimate your body fat percentage with the U.S. Navy circumference method. Enter a few tape measurements to see your body fat %, category, and — if you add your weight — your fat mass and lean mass, in metric or imperial units.
Understanding the Body Fat Calculator
The Body Fat Calculator estimates your body fat percentage using the U.S. Navy circumference method, a tape-measure technique the military adopted because it needs no special equipment. You enter your height, neck, and waist (women also add the hip), choose metric or imperial units, and the tool returns your body fat percentage plus a fitness category. Add your weight and it also splits your body into fat mass and lean mass. It is a quick, repeatable way to track changes in body composition over time — far more telling than scale weight or BMI alone, since it distinguishes fat from muscle.
How it works
The calculator takes your circumference measurements and converts them to inches (dividing centimeters by 2.54). It then applies the Navy's logarithmic regression formula, which relates the difference between your waist and neck (plus hip for women) and your height to a body fat percentage. The result is clamped to a realistic 2–60% range and matched against gender-specific categories from the American Council on Exercise. If you supply weight, fat mass is your body fat percentage times your weight, and lean mass is whatever remains. The tool validates that waist exceeds neck before calculating, so impossible inputs return a friendly prompt rather than a nonsense number.
Worked example
A man stands 70 in (178 cm) tall with a 15 in (38 cm) neck and a 34 in (86 cm) waist. Plugging in: 86.010 × log10(34 − 15) − 70.041 × log10(70) + 36.76 ≈ 17.7% body fat, landing him in the Fitness category. If he weighs 165 lb, that is roughly 29 lb of fat mass and 136 lb of lean mass. Trimming his waist to 32 in would drop the estimate to about 13%, into the Athletes range.
Tips & common mistakes
- Measure on bare skin with a flexible tape held snug but not compressing the skin, and breathe normally — don't suck in your stomach.
- Take each measurement two or three times and use the average; a half-inch error on the waist can shift the result by a full percentage point.
- Measure the neck just below the larynx, the waist at the navel for men and the narrowest point for women, and the hip at the widest part of the buttocks.
- Always track yourself at the same time of day, ideally in the morning before eating, so changes reflect body composition rather than meals or water.
- Use this as a trend tracker, not an exact reading — the Navy method can differ from a DEXA scan by several percentage points for any one person.
- Pair it with BMI and waist measurements for a fuller picture, and consult a professional before acting on any single number.
Sources & methodology
- • U.S. Navy body fat circumference method (Hodgdon & Beckett, Naval Health Research Center)
- • American Council on Exercise (ACE) body fat percentage categories
Related tools
Reviewed by the TopOpenTools editorial team · Last updated June 2026. These tools provide general estimates for educational purposes only and are not financial, tax, insurance, investment, or medical advice. Verify important decisions with a qualified professional.
How to Use This Calculator
- 1Choose your gender and units (cm or inches).
- 2Measure your height, neck, and waist (women also the hip) and enter them. Add weight to see fat and lean mass.
- 3Click Calculate Body Fat, then cross-check with the BMI calculator.
Frequently Asked Questions
How accurate is the Navy body fat method?
It is a solid estimate from simple tape measurements, typically within about 3–4% of methods like DEXA for most people. It is less precise than DEXA or hydrostatic weighing, and accuracy depends on measuring at the right spots, so treat the number as a guide rather than an exact figure.
What measurements do I need?
Everyone needs height, neck, and waist. Women also measure the hip. Use a flexible tape held snug but not tight: neck just below the larynx, waist at the navel for men and the narrowest point for women, and hip at the widest part. Weight is optional and only used to show fat mass and lean mass.
Is this medical advice?
No. This calculator gives an estimate of body fat percentage for general fitness tracking only. It is not a diagnosis and does not replace a professional assessment. Talk to a doctor or qualified professional before making decisions about your health, diet, or training.