Data Source & Methodology

This calculator provides estimates based on established formulas. It is not a substitute for professional medical advice or a clinical assessment (like a DEXA scan).

Our calculations are rigorously based on the following peer-reviewed sources:

  • U.S. Navy Method: The formula and methodology from the 1984 Naval Health Research Center report: Hodgdon, J. A., & Beckett, M. B. (1984). Prediction of percent body fat for U.S. Navy men and women (No. NAVHLTHRSCH-TR-84-11). Naval Health Research Center. This method uses body circumference measurements.
  • BMI-Based Method: A formula derived from studies by Deurenberg et al., which estimates body fat from Body Mass Index (BMI), age, and gender. Deurenberg, P., Weststrate, J. A., & Seidell, J. C. (1991). Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. British journal of nutrition, 65(2), 105-114.

All calculations are based strictly on the formulas and data provided by these sources.

The Formulas Explained

All calculations are performed using metric units (cm, kg). Imperial inputs are converted first.

U.S. Navy Method

The U.S. Navy method uses different formulas for men and women.

For Men:

$$BFP \% = 86.010 \times \log_{10}(\text{waist}_{cm} - \text{neck}_{cm}) - 70.041 \times \log_{10}(\text{height}_{cm}) + 36.76$$

For Women:

$$BFP \% = 163.205 \times \log_{10}(\text{waist}_{cm} + \text{hip}_{cm} - \text{neck}_{cm}) - 97.684 \times \log_{10}(\text{height}_{cm}) - 78.387$$

BMI-Based Method (Deurenberg)

This method first calculates your Body Mass Index (BMI) and then uses it to estimate body fat.

Step 1: Calculate BMI

$$BMI = \frac{\text{weight}_{kg}}{\text{height}_m^2}$$

Step 2: Calculate BFP (Gender is a binary value: Male = 1, Female = 0)

$$BFP \% = (1.20 \times BMI) + (0.23 \times \text{Age}) - (10.8 \times \text{Gender}) - 5.4$$

Derived Calculations

Once BFP is found, other metrics are calculated as follows:

$$\text{Fat Mass} = \text{Total Weight} \times (BFP \% / 100)$$ $$\text{Lean Body Mass} = \text{Total Weight} - \text{Fat Mass}$$

Glossary of Variables

Body Fat Percentage (BFP)
The proportion of your total body weight that consists of fat tissue. This is the primary result of the calculator.
Body Fat Mass
The total weight (in kg or lbs) of the fat in your body.
Lean Body Mass (LBM)
The weight of all your body components except fat. This includes muscle, bone, water, and organs.
Body Mass Index (BMI)
A simple measure of weight for height, used in one of the calculation methods. It is not a direct measure of body fat.
Neck, Waist, Hip
Circumference measurements used in the U.S. Navy method. Accurate measurement at the correct locations is crucial for this method's accuracy.

How It Works: A Step-by-Step Example

Let's calculate the body fat for a 30-year-old male using the U.S. Navy method.

Inputs:

  • Gender: Male
  • Height: 180 cm
  • Weight: 85 kg
  • Neck: 40 cm
  • Waist: 90 cm

Step 1: Calculate the log values

  • $\text{waist} - \text{neck} = 90 - 40 = 50 \text{ cm}$
  • $\log_{10}(50) \approx 1.699$
  • $\log_{10}(\text{height}) = \log_{10}(180) \approx 2.255$

Step 2: Plug values into the male formula

  • $BFP \% = 86.010 \times 1.699 - 70.041 \times 2.255 + 36.76$
  • $BFP \% = 146.13 - 157.94 + 36.76$
  • $BFP \% \approx 24.95\%$

Step 3: Calculate mass

  • $\text{Fat Mass} = 85 \text{ kg} \times (24.95 / 100) \approx 21.21 \text{ kg}$
  • $\text{Lean Mass} = 85 \text{ kg} - 21.21 \text{ kg} \approx 63.79 \text{ kg}$

Result: The estimated body fat percentage is 25.0% (rounded), which falls into the "Obese" category for men.

Frequently Asked Questions

How accurate is this body fat calculator?

The accuracy depends on the method. The U.S. Navy method has a reported accuracy of ±3-4% for most people, but it requires precise measurements. The BMI-based method is a less accurate, general estimate. No calculator can replace a professional assessment like a DEXA scan.

What is the U.S. Navy method?

The U.S. Navy method (also called the 'DoD method') is a circumference-based formula developed by Hodgdon & Beckett in 1984. It uses tape measurements of height, neck, waist, and (for women) hips to estimate body fat percentage.

Why is my Body Fat Percentage (BFP) different from my BMI?

BMI (Body Mass Index) only measures your weight relative to your height. It cannot tell the difference between muscle and fat. Body Fat Percentage (BFP) specifically estimates the portion of your weight that is fat. An athlete, for example, might have a high BMI (due to muscle) but a low BFP.

How should I measure my waist, neck, and hip?

For accurate results, be consistent. Use a flexible tape measure (not a metal one).

  • Neck: Measure just below the larynx (Adam's apple), rounding up to the nearest half-inch or 0.5 cm.
  • Waist: For men, measure at the navel. For women, measure at the narrowest point between the ribs and hip bone.
  • Hip (Women only): Measure at the widest point of the hips/buttocks.
All measurements should be taken without sucking in or pulling the tape too tight.

What is a healthy body fat percentage?

Healthy ranges vary by age and gender. Generally, for men, 10-20% is considered healthy or 'fitness'. For women, 20-30% is the equivalent range. Essential fat (the minimum needed for health) is around 2-5% for men and 10-13% for women.

Is this calculator suitable for children or bodybuilders?

No. These formulas were developed for and validated on average adults. They are known to be inaccurate for children, pregnant women, the elderly, and individuals with very high muscle mass (like bodybuilders), as they don't fit the standard assumptions of the model.

Tool developed by Ugo Candido. Health content reviewed by the CalcDomain Health Editorial Board.

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