Body Fat Percentage Calculator

What does body-fat percentage mean?

Body-fat percentage describes the share of total body weight represented by fat mass. This calculator does not measure fat tissue directly: it estimates a percentage from height and circumferences using a classic US Navy equation. It is an accessible way to explore body composition at home, but it is not the same as an instrument-based assessment.

For example, a person weighing 80 kg at an assumed 20% body fat has 16 kg of fat mass and 64 kg of fat-free mass. Fat-free mass includes water, bone and organs as well as muscle. The FFMI calculator relates that mass to height.

How to take tape measurements

Use a non-stretch tape and avoid compressing the skin. Keep it aligned with the measurement plane. Take more than one reading at the same site and repeat if they differ noticeably.

• Neck: Measure just below the larynx with shoulders relaxed.
• Male waist input: Measure the abdomen at navel level.
• Female waist input: Measure the narrowest part of the waist.
• Female hip input: Measure the widest circumference of the hips.

These sites belong to this particular method; do not confuse them with the waist instructions used for the BMI page’s waist-to-height ratio. You can choose centimetres or inches. Measurements are converted to inches inside the equation. If waist is smaller than neck, or the measurements fail to produce a plausible percentage, the tool asks you to check them instead of silently using another method.

US Navy and alternative methods

The main result uses the classic circumference approach associated with Hodgdon and Beckett. The male equation uses height, abdomen and neck; the female equation also uses hips. Its background in military samples does not guarantee equal accuracy for every body type. The National Academies chapter on body composition methods explains this history. This tool does not replace a current military eligibility assessment.

A comparison may also show the Deurenberg estimate based on BMI, age and sex. The two results are not averaged. A large difference is a reason to review the measurements and suitability of the methods, not proof that the higher value is correct.

What is an ideal body-fat percentage?

Age, sex, sport and health circumstances make a single target unsuitable for everyone. The calculator therefore does not assign 10% to all men or 17% to all women. Values observed in athletes are not automatically health targets for every adult.

You can enter a percentage to explore in the optional scenario field. This assumes unchanged fat-free mass; it does not claim that real weight changes will preserve it perfectly.

Scenario weight = fat-free mass ÷ (1 − chosen body-fat fraction). At 80 kg and 20% fat, fat-free mass is 64 kg. A 15% scenario gives 64 ÷ 0.85 = 75.3 kg, a difference of about −4.7 kg. This is not an instruction to lose weight.

Visceral fat and “skinny fat”

A BMI within the reference range does not guarantee low body fat. However, a tape estimate cannot directly measure visceral fat or diagnose “skinny fat” either. Fat distribution and metabolic health require other information. BMI and waist-to-height ratio can provide additional context.

Track changes with the same method, sites and similar conditions. A difference over a few days is not necessarily fat loss. For a broader discussion of nutrition and resistance training, see the guide to increasing muscle mass.