Body Fat Calculator

The body fat calculator estimates the share of fat in your body in two ways: with the U.S. Navy circumference method — from waist, neck (and hip for women) measurements and height — and with a formula based on BMI. You get your body fat percentage, its category by ACE standards, fat mass and lean (fat-free) mass. All calculations run on your device.

How to use the calculator

Enter your sex, height, weight, age and three tape measurements:

  • Neck — below the Adam’s apple, tape horizontal, not compressing the skin;
  • Waist — at navel level, after a normal exhale, tape parallel to the floor, without digging in;
  • Hips — women only: around the widest part of the hips, in underwear or close-fitting clothing.

Measuring takes a couple of minutes. For a stable result, measure in the morning on an empty stomach, at the same time of day, and average 2–3 measurements.

Two methods: U.S. Navy and BMI

The U.S. Navy circumference method uses the ratio of girths: waist and neck for men, plus hips for women. The formula was built on large samples of service members and agrees with reference laboratory methods (hydrodensitometry, DEXA) within about ±3–4 percentage points.

The BMI method is a simplified estimate from height, weight, age and sex (the Deurenberg formula). It cannot tell muscle from fat: for a trained, muscular person it overestimates body fat, and for an older person with muscle loss it underestimates. That is why the calculator shows it for comparison only.

Body fat categories

Your result falls into one of five categories by the ACE (American Council on Exercise) classification. For men:

  • Essential fat deficit — < 6 %;
  • Athlete — 6–13 %;
  • Fitness — 14–17 %;
  • Average — 18–24 %;
  • Above average — ≥ 25 %;

For women the norms are higher: essential fat deficit — below 14 %, athlete — 14–20 %, fitness — 21–24 %, average — 25–31 %, above average — 32 % and more. A woman’s body needs a minimum amount of fat for hormonal function and reproduction — so «athletic» 12 % means completely different things for a woman and for a man.

Why BMI is not enough

BMI is weight in kilograms divided by height in metres squared. It answers the question «does weight match height», but not what the weight consists of. A 180 cm/85 kg man with developed muscles and a man with the same height and weight but mostly fat will both have a BMI of 26.2 — «overweight» — although the first may carry 12 % fat and the second 30 %. Body fat percentage distinguishes these situations: it shows body composition, not just the mass-to-height ratio. That is why sports physicians rely on body fat percentage, not BMI, when assessing fitness.

Limitations and accuracy

The U.S. Navy method is convenient at home, but it is an estimate, not a measurement: the error is usually ±3–4 percentage points against reference laboratory methods. Time of day, food and water in the stomach, tape position and tension all affect the result. The method is less accurate at very high obesity and in people with unusual fat distribution. If you need an exact figure (for medical reasons or for competitive sport), use bioimpedance analysis, DEXA or consult a specialist.

The calculation is for information only and is not a medical consultation.

Frequently asked questions

How is the U.S. Navy method different from BMI?
BMI is weight divided by height squared: it estimates whether mass matches height, but cannot tell muscle from fat. Two people with a BMI of 26 may carry 12 % and 30 % fat. The U.S. Navy method works from waist, neck (and hip for women) girths: the ratio of girths reflects actual fat stores, so for estimating body composition it is noticeably more informative than BMI. In this calculator the BMI method is shown for comparison only — rely on the Navy figure.
How accurate is the U.S. Navy method?
The error is usually ±3–4 percentage points against reference laboratory methods (hydrodensitometry, DEXA). Accuracy depends on careful measuring: the tape should lie snugly but not dig in, the waist is measured at navel level after an exhale, the neck — below the Adam’s apple, horizontally. The spread of repeated measurements for one person during a day is 1–2 pp (lower in the morning than in the evening). That is enough to track dynamics: compare measurements taken at the same time of day by the same method.
Where exactly should I measure my waist, neck and hips?
Measure the waist at navel level, standing straight, after a calm exhale — tape parallel to the floor, pressed but not cutting in. The neck — below the Adam’s apple, tape horizontal around the neck; look straight ahead, do not tilt your head. Hips (women) — around the widest part, standing with feet together. Measure in the morning on an empty stomach, in light clothing or underwear — that keeps the numbers comparable from one measurement to the next.
How do I lower my body fat percentage?
The base is a moderate calorie deficit (usually 10–20 % of your norm): without it, no workout will «burn» fat locally. Add strength training 2–3 times a week (muscles support metabolism in a deficit) and 150+ minutes of moderate cardio per week. Protein — 1.6–2 g per kg of body weight, so that you lose mostly fat, not muscle. Aim to lose 0.5–1 % of fat per month — sustainable, without breakdowns. Rush, starvation diets and «fat burners» shed water and muscle, not fat.
Why are body fat norms higher for women than for men?
A woman’s body needs a larger essential fat reserve — at least 10–12 % versus 2–4 % for men. Fat tissue takes part in the synthesis of sex hormones (estrogens), supports the menstrual cycle, fertility and pregnancy. In women fat is physiologically stored on the hips and buttocks (gynoid type), in men — on the abdomen (android type). That is why «Athlete» means 6–13 % for men but 14–20 % for women: 10 % body fat in a woman is already a deficit with a risk of hormonal disruption.
What are the risks of too low body fat?
Below the essential minimum (≈2–4 % for men, ≈10–12 % for women) the hormonal and immune systems suffer: testosterone and estrogen production drops, the cycle and fertility are disrupted in women, immunity falls, skin condition, mood and libido worsen, and the risk of osteoporosis rises. In athletes, a long-term fat deficit leads to relative energy deficiency (RED-S): performance drops, injuries become frequent, heart rhythm is disturbed. A very low body fat percentage is maintained briefly and only under specialist supervision — it is a state for a competitive peak, not for life.

Updated: Oct 29, 2026

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