Body Fat Percentage Calculator (Basic)

Body fat percentage calculator using simple tape measurements

Body fat percentage is a rough estimate of how much of your body weight is made up of fat, expressed as a percentage. Unlike scale weight alone, body fat percentage helps you separate changes in fat from changes in lean mass. This matters because you can lose weight while losing muscle, or stay the same weight while improving body composition.

This calculator uses a basic version of the US Navy tape method. It estimates body fat percentage from a small set of measurements you can take at home with a flexible tape measure. You select your sex, pick metric or imperial units, then enter height, weight, waist, and neck. If you select female, you also enter hip circumference. The calculator then estimates your body fat percentage, your fat mass, and your lean mass.

The results are best used for tracking trends over time, not as a single definitive number. If you measure the same way each time, under similar conditions, you can spot whether you are moving in the right direction. If your goal is fat loss, the most useful signal is whether your estimated body fat percentage and fat mass are trending down while strength and performance stay stable.

Assumptions and how to use this calculator

• This is an estimate based on population formulas, not a clinical measurement. Treat it as an approximation.
• Use a soft measuring tape and measure on bare skin or over thin clothing. Keep tape level and snug, not tight.
• Measure consistently. Use the same locations, the same tape, and ideally the same time of day.
• Waist and hip should be measured at the widest or most relevant point for your body shape, and repeated the same way each time.
• The formula assumes average body fat distribution patterns for male and female groups. Individuals can deviate.

Common questions

Where exactly should I measure my waist, neck, and hips?

For most people, waist is measured around the abdomen at a consistent point you can find again easily. Many people use the level of the navel, while others use the narrowest point of the waist. The key is consistency, not picking the perfect textbook location. Neck is measured just below the Adam’s apple with the tape level. For hips (female only), measure around the widest part of the buttocks with the tape level all the way around.

Why does sex change the formula?

The method accounts for typical differences in fat distribution patterns. The female formula uses hip circumference because it improves the estimate for many women. This does not mean every person fits the pattern perfectly. It is simply how the tape method attempts to model body composition with limited data.

How accurate is the US Navy tape method?

Accuracy varies by person and by measurement quality. For many people, the method is good enough to track change over time if you measure consistently. It can be off by several percentage points in either direction, especially if you carry fat in uncommon patterns or if measurements are inconsistent. If you need a higher precision measurement, consider professional methods like DEXA, hydrostatic weighing, or calibrated skinfold testing.

What is fat mass and lean mass, and why do they matter?

Fat mass is your estimated weight of body fat. Lean mass is everything else, including muscle, bone, organs, and water. If you are cutting weight, tracking fat mass helps you see whether weight loss is likely coming from fat. If you are bulking, tracking lean mass trends can help you see whether weight gain might be coming from muscle rather than fat.

How often should I measure and track body fat?

Weekly or every two weeks is usually enough. Daily measurements can be noisy because hydration and digestion can change measurements slightly. If you track weekly, take measurements at the same time of day, ideally under similar conditions, and focus on the trend across several data points rather than any single reading.