Body Fat Calculator

What is a body fat calculator?

A body fat calculator estimates how much of your total body weight is fat mass. Unlike a simple weight scale, body fat percentage gives a better sense of body composition because it separates fat mass from lean body mass, which includes muscle, bone, water, and organs.

This calculator works as a body fat percentage calculator, fat mass calculator, lean body mass calculator, BMI-based body fat estimator, U.S. Navy body fat calculator, and general body composition tool. It includes two methods so you can choose whichever fits the information you have available: precise circumference measurements, or just your basic height, weight, age, and gender.

How this body fat calculator works

The U.S. Navy method uses body measurements — height, waist, and neck for men, with an added hip measurement for women — to estimate body density and body fat percentage. It tends to track real body composition more closely than BMI-based estimates because it directly measures where body fat tends to accumulate, rather than only comparing total weight to height.

The BMI-based method is simpler and only needs height, weight, age, and gender, making it useful when you do not have a measuring tape handy or just want a quick approximation. It can be less accurate for athletes, bodybuilders, very muscular individuals, older adults, and anyone whose body composition differs noticeably from average assumptions built into the formula.

U.S. Navy and BMI-based formulas

For men, the Navy method uses height, waist, and neck. For women, it adds a hip measurement:

The BMI-based estimate instead relies on BMI, age, and gender:

Because the Navy formula is measurement-based, small errors in how you measure waist, neck, or hip circumference can shift the result noticeably. Keep the tape snug but not compressed, take each measurement at the same spot every time, and measure at a similar time of day for the most consistent tracking over weeks or months.

How to measure correctly

1. Measure height without shoes.
2. Measure weight in the morning if possible, before eating or drinking.
3. Measure waist around the navel area or the narrowest point of the waist.
4. Measure neck just below the larynx, keeping the tape level.
5. For women, measure hip circumference around the widest part of the hips.
6. Keep the tape flat, level, and snug without pulling it tight.

Why body fat percentage matters for fitness tracking

Body fat percentage helps explain fat loss, muscle gain, fitness progress, and body composition changes in a way that the scale alone cannot. Two people can share the same BMI while having very different muscle mass and fat mass, which is why relying on body weight alone can be misleading during a training or nutrition program.

If you are tracking body composition alongside broader fitness or nutrition goals, pairing this tool with the TDEE Calculator can help you set an appropriate calorie target for fat loss or muscle gain, while the Protein Intake Calculator can help you plan protein intake to support lean mass while losing fat. The BMI Calculator is also worth checking alongside this tool, since comparing BMI and body fat percentage side by side often gives a clearer picture than either number alone. If your goal involves training for endurance events, the Marathon Finish Time Calculator can help you plan pacing as your body composition changes over a training cycle.

Important health note

This calculator is for educational and informational use only. It cannot replace professional body composition testing such as a DEXA scan, skinfold caliper testing performed by a trained professional, hydrostatic weighing, or bioelectrical impedance analysis. If you are concerned about your body fat, weight, hormones, diet, or general health, speak with a qualified healthcare professional before making significant changes.