Why body fat is more telling than BMI
BMI only compares weight with height, so it can’t tell fat from muscle; a muscular athlete can come out “overweight”. Body fat measures how much of your weight is actually fat, so it’s a better indicator of health and shape.
The formula (US Navy)
- Men: 495 ÷ (1.0324 − 0.19077 × log(waist − neck) + 0.15456 × log(height)) − 450
- Women: 495 ÷ (1.29579 − 0.35004 × log(waist + hip − neck) + 0.22100 × log(height)) − 450
All measurements in centimetres; “log” is the base-10 logarithm. The categories table follows the American Council on Exercise (ACE).
How to measure correctly
- Neck: just below the Adam’s apple, tape sloping slightly down at the front.
- Waist: men at navel level, women at the narrowest point, standing relaxed without sucking in.
- Hips (women): at the widest point of the buttocks.
- Measure everything twice and use the average.
Worked examples
- A man 178 cm and 85 kg, waist 92 cm, neck 38 cm: about 21.5% body fat (average) — 18.3 kg of fat and 66.7 kg of lean mass.
- A woman 163 cm and 65 kg, waist 76 cm, hips 98 cm, neck 33 cm: about 29.5% body fat (average) — 19.2 kg of fat.
How accurate is it?
The US Navy method is an estimate from tape measurements, not a lab test, and can differ from methods such as DEXA by a few percentage points. Its real value is tracking: measure the same way at the same time (for example in the morning before eating) every 2–4 weeks, and follow the trend rather than a single number.
Frequently Asked Questions
My result looks odd. Why?
Usually the measurement. A 2 cm difference in waist can change the result noticeably. Make sure the tape is level, not too tight, and on bare skin.
What is a healthy body fat percentage?
Roughly 14–24% for men and 21–31% for women are generally considered healthy ranges. Women naturally carry more fat than men for hormonal and reproductive reasons.
I want to lower my body fat. Where do I start?
Find your calorie needs and eat a little below them, get enough protein to keep your muscle, and do resistance training.
Why is my weight dropping but not my body fat?
You may be losing muscle along with fat. Make sure you eat enough protein (see the macro calculator) and do resistance training, so the loss comes from fat.
Are smart scales more accurate?
Scales that estimate body fat with a small electric current are affected by how much water is in your body, so their reading changes through the day. Whatever method you choose, stick to it so comparisons are fair.