Body Fat Calculator
Estimate your body fat percentage from neck, waist and hip measurements, or from your BMI. See your category, fat and lean mass, and a healthy range for your age.
Your results
Enter your details above to see results.
Healthy range for your age
Where you sit
Fat mass
Lean mass
BMI
Method
Estimates only. Body fat formulas can be off by several percentage points and are not a medical diagnosis. Speak to a healthcare professional about your health.
What is body fat percentage?
Body fat percentage is the share of your total weight that is fat. The rest, called lean mass, is made of muscle, bone, organs and water. Some fat is essential for hormones, temperature control and protecting organs. Too much, especially around the waist, is linked to higher risk of heart disease and type 2 diabetes. Unlike BMI, body fat percentage can tell a muscular person from a person with excess fat at the same weight.
The U.S. Navy method
This method was developed by the U.S. Navy to estimate body fat from simple tape measurements. It uses the logarithm of the difference between your waist and neck (and your hip for women) together with your height. In metric units the equations are:
Men: 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
Accuracy is usually within a few percentage points of more precise methods. It can be less accurate for very muscular or very lean people, and results depend on measuring consistently.
How to measure
- Use a flexible, non-stretch tape and keep it snug but not tight.
- Measure in the morning, before eating, and stand relaxed.
- Take each measurement three times and use the average.
- Measure on bare skin and keep the tape level with the floor.
The BMI-based estimate
If you have no tape measure, the calculator can use the Deurenberg equation, which estimates body fat from BMI, age and sex. It is quick but less personal, since it cannot see where your weight sits. Treat it as a rough guide only.
Body fat categories
| Category | Women | Men |
|---|---|---|
| Essential fat | 10-13% | 2-5% |
| Athletes | 14-20% | 6-13% |
| Fitness | 21-24% | 14-17% |
| Average | 25-31% | 18-24% |
| Higher body fat | 32% and above | 25% and above |
Healthy ranges also rise gradually with age, which is why the calculator shows a range for your age group as well.
Worked Example: Navy Method
Man: height 180 cm, waist 90 cm, neck 38 cm. The waist minus neck is 52 cm, and the formula gives about 19.8% body fat.
Woman: height 165 cm, waist 75 cm, hip 98 cm, neck 32 cm. Waist plus hip minus neck is 141 cm, and the formula gives about 28.9% body fat.
These are illustrations of the method with made-up measurements. Your own numbers and the calculator above will give your result.
Healthy Body Fat Range by Age
Ranges rise slightly with age. The table shows the healthy ranges from Gallagher et al., the study the calculator cites, which link body fat to a BMI of 18.5 to 24.9.
| Age | Women | Men |
|---|---|---|
| 20 to 39 | 21 to 32% | 8 to 19% |
| 40 to 59 | 23 to 33% | 11 to 21% |
| 60 to 79 | 24 to 35% | 13 to 24% |
Fat Mass and Lean Mass Example
Body fat percentage turns into kilograms with a simple sum. At 80 kg and 20% body fat, fat mass is 80 × 0.20 = 16 kg and lean mass is 64 kg. If your lean mass stayed the same and you wanted 15% body fat, your weight would be 64 / 0.85 = about 75.3 kg, which means losing around 4.7 kg of fat. Real changes are never exactly this tidy, because lean mass also shifts with training and diet.
Where to Place the Tape
For the Navy method, measure the neck just below the larynx, sloping slightly down at the front. Men measure the waist at the navel and women at the narrowest point, and women also measure the hip at the widest point. Keep the tape flat and snug without pressing into the skin. Repeat each measurement and use the average, because a difference of 1 cm at the waist can move the result by a few tenths of a percent.
Body Fat Methods Compared
| Method | What it uses | Notes |
|---|---|---|
| Navy tape method | Height, neck, waist (and hip for women) | Free and repeatable at home; less accurate for very muscular or very lean people |
| BMI-based estimate | Height, weight, age, sex | Quick but cannot see where weight sits |
| Smart scale | Electrical resistance | Changes with hydration; compare only with itself |
| Skinfold calipers | Fat thickness at several sites | Depends on the skill of the person measuring |
| DEXA scan | Low-dose X-ray | More precise, but needs a clinic |
Whichever method you choose, repeat it under the same conditions (same time of day, same tape or scale) and look at the trend over weeks rather than a single reading.
This page is for general information and is not medical advice. If you are concerned about your weight or body composition, speak to a doctor or registered dietitian.
Frequently asked questions
How accurate is the Navy body fat calculator?
It is usually within about 3 to 4 percentage points of more advanced methods such as DEXA for many people. It is a good way to track change over time if you measure the same way each time.
What is a good body fat percentage?
It depends on age, sex and goals. For adults aged 20 to 39, a healthy range is roughly 8-19% for men and 21-32% for women. Athletes may be lower, and the range rises with age.
Why do women have a higher body fat percentage?
Women naturally carry more essential fat, which supports hormones and reproductive health. That is why the ranges for women are higher at every category.
Can I use this calculator if I am pregnant or under 18?
No. These formulas are made for non-pregnant adults. Speak to a healthcare professional for guidance.
Why is my result different from my smart scale?
Smart scales estimate body fat using electrical resistance, which is affected by hydration. Different methods can easily differ by several percentage points. Pick one method and use it consistently.
Is my data saved or shared?
No. Everything is calculated in your browser and nothing you enter is uploaded or stored.
How often should I measure body fat?
Every two to four weeks is enough. Day-to-day changes are mostly water, and the tape method is not precise enough to show small differences between days.
Why does the Navy method use the neck?
The neck is a rough guide to lean tissue in the upper body. Subtracting it from the waist measurement makes the result depend on how much of your waist is fat compared with frame size.
Can body fat be too low?
Yes. Essential fat is needed for hormones, temperature control and organ protection, and levels below the essential range can affect health. The table of categories above shows the lowest ranges.
How can I lower my body fat percentage?
The general approach in health guidelines is a modest calorie deficit, enough protein and resistance training to keep muscle. Individual needs differ, so a doctor or dietitian can give personal advice.
Is the Navy method better than the BMI estimate?
Usually yes, because it uses a waist measurement and so reflects where weight is carried. The BMI estimate is a rough fallback when you cannot measure.
Sources and further reading
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, Reports 84-11 and 84-29. 1984.
- Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. British Journal of Nutrition. 1991;65(2):105-114.
- Gallagher D, et al. Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. American Journal of Clinical Nutrition. 2000;72(3):694-701.
- American Council on Exercise. What are the guidelines for percentage of body fat loss?