Body Fat CalculatorFree online fitness & health calculator — instant results, no sign-up
Estimate body fat using the U.S. Navy tape method.
For general information only. This is not medical advice, diagnosis, dosing guidance or a treatment recommendation. Talk to a doctor or other qualified health professional about your health, pregnancy, or diet.
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How the result changes with age
Each row below was calculated with this tool, keeping every other input at its default and changing only age from half to one and a half times the default value. Use it to see how sensitive the answer is before you enter your own numbers.
| Age (years) | Body fat | Category | Fat mass |
|---|---|---|---|
| 15 | 17.7% | Fitness | 13.3 kg |
| 23 | 17.7% | Fitness | 13.3 kg |
| 30 (default) | 17.7% | Fitness | 13.3 kg |
| 38 | 17.7% | Fitness | 13.3 kg |
| 45 | 17.7% | Fitness | 13.3 kg |
About the Body Fat Calculator
This calculator estimates body fat percentage, fat mass, and lean mass using the U.S. Navy circumference-based method. It provides a practical body composition assessment for fitness enthusiasts and individuals monitoring changes in muscle and fat tissue.
- Age
- Age of the individual in years (typically 18 to 80).
- Sex
- Biological sex (Male or Female), which determines the formula and body composition categorization.
- Height
- Standing height measured in centimeters.
- Weight
- Total body weight measured in kilograms.
- Neck
- Neck circumference in centimeters, measured just below the larynx (Adam's apple).
- Waist
- Waist circumference in centimeters, measured horizontally at the navel for men or narrowest point for women.
- Hip (women)
- Hip circumference in centimeters, measured at the widest point across the buttocks (used only for females).
Formula and method
Men: Body Fat % = 495 / (1.0324 - 0.19077 × log10(waist - neck) + 0.15456 × log10(height)) - 450 Women: Body Fat % = 495 / (1.29579 - 0.35004 × log10(waist + hip - neck) + 0.22100 × log10(height)) - 450 Fat mass = weight × (Body Fat % / 100) Lean mass = weight - Fat mass
- heightStanding height in centimeters
- weightTotal body weight in kilograms
- neckNeck circumference in centimeters
- waistWaist circumference in centimeters
- hipHip circumference in centimeters (used for women)
- log10Common logarithm (base 10)
The tool applies the empirical U.S. Navy equations using logarithmic ratios of body circumferences and height to estimate body density and fat percentage. It then calculates fat mass and lean mass from total body weight, categorizing results into Essential, Athletes, Fitness, Average, or Obese based on sex-specific thresholds.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Age30 years
- SexMale
- Height175 cm
- Weight75 kg
- Neck38 cm
- Waist86 cm
Results
- Body fat17.7%
- CategoryFitness
- Fat mass13.3 kg
- Lean mass61.7 kg
How to use the Body Fat Calculator
- 1Measure circumference dimensions (neck, waist, and hips for women) along with height and body weight.
- 2Calculate body fat percentage using the sex-specific logarithmic U.S. Navy formula.
- 3Multiply total body weight by body fat percentage to find fat mass in kilograms.
- 4Subtract fat mass from total body weight to determine lean mass and assign the classification category.
Reading your result
The body fat percentage indicates what proportion of your total weight consists of adipose tissue. The category shows where you fall relative to general fitness standards, while fat mass and lean mass break down your total scale weight into fat versus fat-free tissues (muscle, bone, and water).
Limitations
The equation relies on tape measurements and assumes standard body fat distribution patterns, which may lead to inaccuracies in individuals with disproportionate muscular development or atypical fat storage. Small variations in tape tension or measurement placement can also notably alter logarithmic results.
Common questions
Why are hip measurements only required for women?+
Biological fat distribution patterns differ between sexes; women generally carry more subcutaneous adipose tissue around the pelvic and gluteal regions, making hip circumference a critical variable in the female U.S. Navy model.
What constitutes lean mass?+
Lean mass, or fat-free mass, includes all non-fat body components such as skeletal muscle, bones, organs, connective tissue, and bodily fluids.
How precise do the circumference measurements need to be?+
Because the formula utilizes base-10 logarithms, errors of even 1 to 2 centimeters in circumference can alter the final body fat estimate by several percentage points. Keep the measuring tape level and snug against the skin without compressing soft tissue.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.