Body Fat Calculator Using the US Navy Method

How to use the body fat calculator

1. Select your sex and preferred unit (centimeters or inches).
2. Enter your height, neck and waist circumferences following the measurement hints.
3. If you selected Female, enter your hip circumference at the widest point.
4. Optionally add your weight to see estimated fat mass and lean mass.
5. Read your estimated body fat percentage in the results below.

How the US Navy method works

The US Navy body fat formula uses simple circumference measurements to estimate body composition without calipers or water displacement. The equations differ by sex because men and women store fat differently.

For men, the formula is:

BF% = 495 / (1.0324 - 0.19077 * log10(waist - neck) + 0.15456 * log10(height)) - 450

For women, it adds the hip measurement:

BF% = 495 / (1.29579 - 0.35004 * log10(waist + hip - neck) + 0.22100 * log10(height)) - 450

All measurements must be in centimeters. If you enter inches, this body fat calculator converts them first by multiplying by 2.54. For example, a man who is 175 cm tall with an 85 cm waist and 38 cm neck has a log10(85 - 38) of about 1.672 and a log10(175) of about 2.243. Plugging those into the male equation yields roughly 16.9 percent body fat.

How to take accurate measurements

The accuracy of any body fat percentage estimate depends entirely on how carefully you measure. Use a flexible, non-stretchable tape measure and keep it snug against the skin without compressing the tissue.

• Neck: Place the tape just below the larynx (Adam's apple), perpendicular to the long axis of the neck. Keep your shoulders relaxed and look straight ahead.
• Waist (men): Measure horizontally at the level of the navel while standing normally. Do not suck in your stomach.
• Waist (women): Measure horizontally at the narrowest part of the abdomen, usually above the navel.
• Hips (women): Measure around the widest portion of the buttocks, keeping the tape parallel to the floor.
• Height: Stand barefoot against a wall, heels together, looking straight ahead. Measure from the floor to the top of the head.

Take each measurement two or three times and use the average. Even a one-centimeter error in the waist can shift the result by a full percentage point.

Body fat percentage categories

Once you have your number from the body fat calculator, compare it against standard reference ranges. These categories come from guidelines widely used in fitness and clinical settings.

Women naturally carry more essential fat than men due to reproductive physiology. Dropping below the essential fat range is dangerous regardless of athletic goals.

Limitations of circumference methods

The US Navy method was developed for military populations and validated against hydrostatic weighing. It works reasonably well for people of average build, but it has known blind spots. Very muscular individuals may receive inflated body fat estimates because the formula interprets large circumferences as fat rather than muscle. Conversely, older adults who have lost muscle mass but retained visceral fat might see deceptively low numbers if their waist stays small.

This tool does not replace clinical assessments like DEXA scans or Bod Pod measurements. It provides a fast, zero-cost screening estimate. If you are tracking changes over time, consistency matters more than absolute precision: always measure under the same conditions, ideally in the morning before eating.

For broader health context, many people pair body composition data with other metrics. A BMI calculator gives a quick weight-to-height ratio, while a TDEE calculator estimates daily energy needs based on activity level. Neither measures fat directly, which is why circumference-based formulas remain popular for home use.

From body fat to fat mass and lean mass

If you provide your weight, the calculator splits it into fat mass and lean mass. The math is straightforward:

Fat mass = Weight * (Body fat % / 100)

Lean mass = Weight - Fat mass

For instance, an 80 kg person with 16.9 percent body fat carries about 13.6 kg of fat mass and 66.4 kg of lean mass. Lean mass includes muscle, bone, organs and water. Tracking lean mass over time helps distinguish genuine fat loss from muscle loss during a calorie deficit. Pairing this data with a water intake calculator can support hydration planning, since lean tissue holds significantly more water than adipose tissue.

An estimate, not medical advice

The body fat calculator uses a standard published formula, and formulas describe averages, not you. Age, body composition, medical conditions, medication, pregnancy and training history can all move the real number. Use the result as a starting point for planning, and speak to a doctor, dietitian or qualified coach before making health, diet or training decisions, especially if you have a medical condition.

Worked examples

Each result below was produced by the same code the tool runs, so you can check your own numbers against them.