Body Fat Calculator
Use this body fat calculator to estimate your body fat percentage from tape measurements using the U.S. Navy method.
Updated October 22, 2026
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Body Fat Percentage Is Calculated
A DEXA scan is one of the most accurate ways to measure body fat, but it requires special equipment most people will never have access to. This calculator uses a tape-measure alternative originally developed for the U.S. Navy, which trades some precision for something you can do at home in a few minutes with nothing but a tape measure.
What This Calculator Measures
This estimates body fat percentage from a handful of circumference measurements. It’s a screening estimate, not a diagnostic measurement, and works best for tracking your own trend over time rather than comparing your exact number against someone else’s scan result.
The Formula
This calculator uses the U.S. Navy Circumference Method, developed at the Naval Health Research Center to give military personnel a field-expedient way to assess body fat without lab equipment¹.
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
All measurements in both formulas are in inches. If you measure in centimeters, the calculator converts them for you.
The formula was built from regression analysis on a large sample of Navy personnel who were also hydrostatically weighed, the underwater-submersion technique that was the practical gold standard before DEXA became widely available¹,⁵. The waist-to-neck difference does most of the predictive work, since a wider waist relative to your neck circumference is a reasonably strong proxy for central fat accumulation across a large population, even though it says nothing about any one individual’s fat distribution specifically.
How This Calculator Computes Your Result
Enter your sex, height, neck, and waist measurements (plus hip for women). We run the formula above directly and round to one decimal place, then match your result against the category bands below.
What Your Result Means
Category | Men | Women |
Essential Fat | 2 to 5% | 10 to 13% |
Athletes | 6 to 13% | 14 to 20% |
Fitness | 14 to 17% | 21 to 24% |
Acceptable | 18 to 24% | 25 to 31% |
Obese | 25% and above | 32% and above |
These practitioner categories come from the American Council on Exercise³, and align closely with academic body fat ranges linked to healthy BMI categories in a large clinical sample². Essential fat is the minimum needed for basic physiological function, hormone production, organ protection, and cell membrane integrity, and dropping below it for extended periods carries real health risk regardless of how lean it might look.
How to Measure Correctly
Measure your neck just below the larynx. Men measure the waist at the navel. Women measure the waist at its narrowest point, usually about halfway between the navel and the bottom of the breastbone, and the hips at the widest point of the buttocks. Keep the tape snug but not compressing the skin, and measure at the end of a normal breath for consistency. Take each measurement twice and average the results.
Why Circumference Methods Work at All
The Navy formula isn’t the only circumference-based approach with research behind it. Independent regression equations developed from hydrostatic weighing data in over 500 men and nearly 500 women found that combinations of waist, hip, and other girths could predict body density with standard errors in a similar range⁴,⁶, which is part of why circumference-based estimation has held up as a reasonably validated field method rather than a one-off shortcut.
Body Fat Percentage Chart
The American Council on Exercise categories from the table above. Enter your result to mark it.
- Essential Fat
- Athletes
- Fitness
- Acceptable
- Obese
Show data table
| Sex | Essential Fat | Athletes | Fitness | Acceptable | Obese |
|---|---|---|---|---|---|
| Men | 2 to 5% | 6 to 13% | 14 to 17% | 18 to 24% | 25% and above |
| Women | 10 to 13% | 14 to 20% | 21 to 24% | 25 to 31% | 32% and above |
Body Fat Ranges by Age
Body fat percentages that correspond to the adult BMI categories, by age. Healthy ranges shift upward with age.
- Low BMI below 18.5
- Healthy BMI 18.5 to 24.9
- Overweight BMI 25 to 29.9
- Obese BMI 30 and above
Show data table
| Age | Low | Healthy | Overweight | Obese |
|---|---|---|---|---|
| Age 20–39 | under 21% | 21 to 33% | 33 to 39% | 39% and above |
| Age 40–59 | under 23% | 23 to 34% | 34 to 40% | 40% and above |
| Age 60–79 | under 24% | 24 to 36% | 36 to 42% | 42% and above |
A Note on Accuracy
The original Navy studies report a correlation with hydrostatic weighing of about r = 0.90 for men and 0.85 for women¹,⁵, with a typical error margin of about 3 to 4 percentage points. That's solid for a tape-measure method, but it's still an estimate, not a direct measurement, and accuracy tends to decrease at the extremes, very lean or very muscular individuals in particular. Measure consistently, without pulling the tape too tightly, and use repeated checks over time rather than fixating on any single reading.
Frequently Asked Questions
How accurate is the Navy method?
Generally accurate within a few percentage points for most people, with published correlations around r = 0.90 against hydrostatic weighing¹, though it can be less precise for very lean or very muscular individuals whose waist-to-neck ratio doesn't follow the typical pattern the formula was built on.
What measurements do I need?
Your neck and waist circumference (plus hip circumference for women), along with your height. Consistent measuring technique matters more than the exact tape used.
Is this as accurate as a DEXA scan or calipers?
No single field method matches lab-grade tools like DEXA or hydrostatic weighing, but the Navy method is a solid, repeatable estimate for tracking change over time¹.
How often should I re-measure?
Every 4 to 6 weeks is usually enough to see a meaningful trend without over-focusing on normal day-to-day fluctuation.
Sources
Prediction of Percent Body Fat for U.S. Navy Men from Body Circumferences and Height, Hodgdon & Beckett, 1984
Healthy Percentage Body Fat Ranges: An Approach for Developing Guidelines Based on Body Mass Index, Gallagher et al., 2000
Body Fat Percentage Norms, American Council on Exercise
Predicting Body Composition of Men from Girth Measurements, Tran & Weltman, 1988
Prediction of Percent Body Fat for U.S. Navy Women from Body Circumferences and Height, Hodgdon & Beckett, 1984
Generalized Equation for Predicting Body Density of Women from Girth Measurements, Tran & Weltman, 1989