Body Fat Calculator
Enter a few body measurements to estimate your body fat percentage using the U.S. Navy method.
Reviewed by the ToolNestr Editorial Team — July 2026
Fill in your measurements to estimate body fat.
⚕️ For general information only — not medical advice.
About body fat percentage
Body fat percentage is often a more useful measure of fitness than weight alone. The U.S. Navy method estimates it from simple tape measurements you can take at home, making it an easy way to track changes over time as you train. Combine it with the BMI Calculator and Calorie Calculator for a complete picture of your health.
When to use this tool
Use the Body Fat Calculator when weight alone isn’t telling you the full story — for example, if you’ve started strength training and want to track fat loss even if the scale doesn’t move. It’s popular with fitness enthusiasts who want a more accurate signal than BMI, and with coaches who need an affordable, repeatable way to monitor client progress without expensive scans.
Tips for best results
- Use a flexible, non-stretchable tape measure and keep it level and snug — not tight enough to compress the skin.
- Take each measurement three times and use the average to reduce error from placement variation.
- Measure at the same time of day (ideally in the morning before eating) for consistent tracking over time.
What different body fat ranges mean
Body fat percentage is typically grouped into categories that reflect fitness level and health risk. The ranges differ for men and women due to biological differences.
Fitness enthusiast
Track changes in body composition that the scale can't show you, especially useful during a recomp or bodybuilding prep phase.
Weight-loss seeker
Monitor whether the weight you're losing is actually fat or just water and muscle, so you can adjust your diet and training accordingly.
Personal trainer
Get an affordable, repeatable body-fat estimate for clients that you can track month to month without expensive DEXA scan appointments.
Health-aware individual
Understand whether your body fat sits in a healthy range and learn where your risk factors lie for conditions linked to excess body fat.
| Category | Men (% body fat) | Women (% body fat) |
|---|---|---|
| Essential fat | 3 – 5% | 10 – 13% |
| Athlete | 5 – 10% | 13 – 18% |
| Fitness | 10 – 14% | 18 – 21% |
| Average | 14 – 18% | 21 – 25% |
| Above average | 18 – 25% | 25 – 32% |
| High | 25%+ | 32%+ |
How body fat percentage is calculated
This calculator uses the U.S. Navy method, a circumference-based approach developed for the U.S. military. It estimates body density from tape measurements of the neck, waist and hips, then converts density to a body fat percentage using the Siri equation.
For men:
Body Fat % = 495 / (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
For women:
Body Fat % = 495 / (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
The formula assumes a two-compartment model (fat mass vs lean mass) and is calibrated for the general adult population. Accuracy is typically within ±3% of hydrostatic weighing when measurements are taken correctly.
Worked example
A 30-year-old man with height 178 cm, neck 39 cm, and waist 88 cm wants to estimate his body fat percentage.
How to use the Body Fat Calculator
Take your measurements
Use a flexible tape to measure your neck, waist and (if female) hips. Keep the tape snug but not compressing the skin.
Enter your height
Add your height and sex, then enter the tape measurements in metric (cm) or imperial (in) as preferred.
Read your estimate
Your estimated body fat percentage and category appear instantly. Use it as a trend marker by measuring monthly under the same conditions.
Tips for accurate body fat measurement
Measure consistently
Always measure at the same time of day (ideally morning, before eating) and under the same conditions. Body water levels affect tape measurements significantly.
Use the right technique
Pull the tape snug but never tight enough to compress the skin. Take each measurement three times and average them to reduce placement errors.
Track trends, not single readings
Body fat changes slowly. A single reading can be misleading — focus on the direction of change over several weeks or months rather than the absolute number.
Frequently asked questions
How accurate is the U.S. Navy method?
It’s a widely used estimate based on tape measurements and is reasonably accurate for most people, though not as precise as a clinical body-composition scan.
Where do I measure?
Neck: just below the larynx. Waist: at the navel (men) or the narrowest point (women). Hip (women): at the widest point. Measure relaxed, without pulling the tape tight.
Is this medical advice?
No — it’s an estimate for general information only.
What is a healthy body fat percentage?
For men, 10–20% is generally healthy; for women, 18–28%. Athletes often fall lower and anything above 25% (men) or 32% (women) is considered above average. Essential fat levels are about 3–5% for men and 10–13% for women.
How often should I measure body fat?
Monthly is ideal — body fat changes slowly, so weekly measurements are usually just noise. Measure at the same time of day and under the same conditions for consistency.
What’s the difference between essential fat and storage fat?
Essential fat is the minimum needed for healthy function (found in nerves, bone marrow, organs) and is higher in women due to childbearing needs. Storage fat is the extra energy reserve under your skin and around organs.
Can body fat percentage be too low?
Yes. Essential fat levels are about 3–5% for men and 10–13% for women. Dropping below these can impair hormone function, bone health, immune response and temperature regulation.
How does age affect body fat percentage?
Body fat naturally increases with age as muscle mass declines, even if your weight stays the same. This is why body composition tracking becomes more informative than the scale as you get older.
What is visceral fat and why does it matter?
Visceral fat is the fat stored deep in your abdomen around your organs. It’s more dangerous than subcutaneous fat because it releases inflammatory substances linked to heart disease and diabetes.
How does body fat distribution affect health risk?
Carrying more fat around the waist (apple shape) is linked to higher cardiovascular risk than carrying it around the hips and thighs (pear shape). Waist-to-hip ratio is a good additional check.