Body Fat Calculator
Estimate your body fat percentage and lean body mass in seconds.
What is it?
Body fat percentage is the proportion of your total body weight that consists of fat tissue. Unlike BMI (Body Mass Index), which only considers height and weight, body fat percentage gives a more complete picture of body composition — distinguishing between fat mass and lean mass (muscle, bone, organs, and water). Two people with the same BMI can have very different body compositions: an athlete with dense muscle may have a "high" BMI but a low body fat percentage, while a sedentary person may fall into the "normal" BMI range but carry an unhealthy amount of fat. This calculator uses two established methods. The US Navy method uses circumference measurements (waist, neck, and hip for women) along with height to estimate body fat percentage using a formula validated by the US Navy. It is one of the most accessible and reliable field methods that does not require specialized equipment. The BMI method uses the relationship between BMI and body fat percentage established in research by Deurenberg et al., adjusted for sex and age. Results are compared against established fitness categories — Essential Fat, Athlete, Fitness, Average, and Obese — based on the American Council on Exercise (ACE) classification system, which is widely used in the fitness industry.
How to use it
- Select your sex (male or female) and enter your age.
- Choose your preferred unit system: metric (cm/kg) or imperial (in/lbs).
- For the US Navy method: measure and enter your height, waist circumference (at the narrowest point), neck circumference, and — for women — hip circumference.
- For the BMI method: enter your height and weight.
- Your estimated body fat percentage, lean body mass, and fat mass appear instantly.
- Check the category chart to see how your result compares to fitness standards.
Why use this tool
Knowing your body fat percentage is more informative than knowing your BMI alone. BMI is a simple ratio that cannot tell the difference between a 90 kg athlete and a 90 kg sedentary person. Body fat percentage answers the real question: how much of your weight is fat, and how much is metabolically active lean tissue? This calculator gives you two independent estimates so you can cross-check them. The US Navy method is widely used by fitness professionals and the military for field assessments. The BMI-based estimate provides a useful secondary reference. If the two methods agree closely, you can have more confidence in the result. The lean body mass figure is particularly useful for fitness planning — it tells you how much of your weight is muscle and bone (what you want to preserve when losing weight) versus fat (what you want to reduce). Everything runs in your browser with no data sent to external servers. Note: these are estimates, not clinical measurements. For precise body composition assessment, consult a healthcare professional and consider methods like DEXA scan or hydrostatic weighing.
Frequently asked questions
What is a healthy body fat percentage?
According to the American Council on Exercise: Essential fat is 2-5% (men) or 10-13% (women). Athlete range is 6-13% (men) or 14-20% (women). Fitness range is 14-17% (men) or 21-24% (women). Average range is 18-24% (men) or 25-31% (women). Above 25% (men) or 32% (women) is classified as obese.
How accurate is the US Navy method?
The US Navy circumference method typically has a margin of error of ±3-4 percentage points compared to laboratory methods like DEXA. This is considered acceptable for field use and fitness tracking. The most important thing is consistency — measuring the same way each time gives you a reliable trend even if the absolute number has some error.
Where exactly should I measure my waist circumference?
For the US Navy method, measure your waist at the narrowest point — typically just above the navel for men, or at the natural waist (narrowest point of the torso) for women. Take the measurement after a normal exhale, without sucking in or pushing out your stomach.
What is lean body mass?
Lean body mass (LBM) is everything in your body that is not fat: muscles, bones, organs, blood, skin, and water. It is the metabolically active part of your body and is directly linked to your resting metabolic rate. Preserving or increasing lean mass while reducing fat is the goal of most body recomposition programs.
How is body fat percentage different from BMI?
BMI (Body Mass Index) is simply weight divided by height squared. It cannot distinguish between fat and muscle. Body fat percentage directly measures the proportion of fat in your total body weight. BMI is a population-level screening tool; body fat percentage is a more individual and actionable measure of body composition.