Body Fat Calculator

What this body fat calculator does

Body fat percentage is the share of your weight that comes from fat. This calculator estimates it with the U.S. Navy circumference method, which uses height, neck, waist, and — for women — hip measurements. It also reports fat mass, lean body mass, an age-based ideal body fat range, and a second estimate based on BMI.

Circumference methods are convenient and inexpensive, but they are estimates. They can be affected by measurement technique, body shape, and where fat is stored.

How to use this calculator

1. Choose US or metric units.
2. Enter age, sex, height, and weight.
3. Measure your neck, waist, and hip. Use a flexible tape measure and keep it level and snug without compressing the skin.
4. Click Calculate to see body fat percentage and body composition estimates.

The default example is a 25-year-old man who is 5 ft 10.5 in tall, weighs 152 lb, and has a 19.5 in neck and 37.5 in waist.

Body fat formulas

The U.S. Navy method uses circumference measurements in inches:

Men:
  body fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76

Women:
  body fat % = 163.205 × log10(waist + hip − neck)
              − 97.684 × log10(height) − 78.387

The BMI method is a separate estimate:

Body fat % (BMI method) =
  1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4

Sex is 1 for men and 0 for women. The calculator shows both estimates because they can differ.

What the results mean

• Body fat percentage: the main U.S. Navy estimate. The default example is 15.3%.
• Fat mass: body fat percentage multiplied by body weight. The default is 23.2 lb.
• Lean body mass: weight minus fat mass. The default is 128.8 lb.
• Ideal body fat for age: an age- and sex-based reference range associated with the Jackson-Pollock data.
• Body fat to lose to reach ideal: the difference between current and ideal fat mass, floored at zero.
• BMI method: a second estimate based on BMI and age.

Assumptions and limitations

The U.S. Navy formula assumes consistent measurement technique. A tape measure placed at the wrong height, pulled too tight, or read at an angle can change the result. The formula is not a DEXA scan, hydrostatic weighing, or air displacement measurement.

The age-based ideal range is a reference, not a personal target. Athletes, older adults, pregnant people, and people with medical conditions may have different healthy ranges. The BMI method is less accurate for very muscular or very lean people.

Frequently asked questions

How accurate is the U.S. Navy method?

It is reasonably consistent when measurements are taken carefully, but it is an estimate. For research or clinical precision, use a DEXA scan or another validated method.

Where should I measure my waist?

Measure at the narrowest point of the torso, usually just above the navel, keeping the tape parallel to the floor. For the Navy method, follow the measurement instructions that accompany the formula.

Why is the BMI method different?

The BMI method uses weight and height rather than circumference, so it captures a different signal. A difference of one or two percentage points between the two methods is common.

Do I need to measure my hip?

The hip measurement is used by the female formula. The calculator includes the field for both sexes so you can switch without re-entering data, but the male formula does not use it.

Reference tables

Body fat categories

Age-adjusted healthy ranges

Weight conversion

Body fat estimates depend on the measurement method. Use the same method for comparison over time.

Source

References:

• CDC — Adult BMI Calculator
• National Heart, Lung, and Blood Institute — Calculate your BMI

Disclaimer

This calculator is for informational and educational purposes only. It is not a medical diagnosis or a substitute for clinical body composition testing. Consult a qualified health professional for personalized advice.