About the Body Fat Calculator
This calculator estimates body fat percentage using the US Navy circumference method, which needs only a tape measure. Body fat percentage tells you what BMI cannot — how much of your weight is fat rather than muscle, bone, and water.
The formula
Men: %BF = 495 / (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450All measurements are in centimetres. The women's equation adds hip circumference, since fat distribution differs. The method was developed by the Naval Health Research Center for fitness screening.
How to use this calculator
- 1Enter your Gender (1=Male, 2=Female). The field starts at
1, which you can overwrite. - 2Enter your Height (cm). The field starts at
178, which you can overwrite. - 3Enter your Waist Circumference (cm). The field starts at
85, which you can overwrite. - 4Enter your Neck Circumference (cm). The field starts at
37, which you can overwrite. - 5Enter your Hip Circumference (cm, females only). The field starts at
95, which you can overwrite. - 6Read the result straight away — it recalculates as you type, so there is no button to press. Use Share to copy a link that reopens the page with your exact numbers filled in.
Worked example
| Input | Value |
|---|---|
| Gender (1=Male, 2=Female) | 1 |
| Height (cm) | 178 |
| Waist Circumference (cm) | 85 |
| Neck Circumference (cm) | 37 |
| Hip Circumference (cm, females only) | 95 |
Result
Body Fat: 17.2%
Category: Fitness
Method: US Navy
Those are the values the page loads with, so you can reproduce this result yourself and then change one field at a time to see what drives the outcome.
Understanding your result
The method works because circumference at specific sites correlates predictably with total fat mass across a population. It typically lands within 3 to 4 percentage points of a DEXA scan, which is good enough to track direction over time and far more informative than weight alone.
Its accuracy depends heavily on measurement technique. Take the tape at the same anatomical landmarks each time, keep it snug but not compressing, and measure at the same time of day. Because the equation is sensitive to the waist-minus-neck difference, a centimetre of inconsistency there shifts the result noticeably — which is why trends matter more than any single reading.
Things worth knowing
- Measure first thing in the morning before eating, when bloating is minimal.
- Take each measurement three times and use the average.
- Essential fat is about 3 to 5 percent for men and 10 to 13 percent for women. Going below that is genuinely dangerous.
- Healthy ranges are roughly 10 to 20 percent for men and 18 to 28 percent for women, rising slightly with age.
- This method is less accurate for very lean or very heavy individuals, where the population equation fits least well.
Frequently asked questions
What is a healthy body fat percentage?+
Broadly 10 to 20 percent for men and 18 to 28 percent for women, with athletes often lower and healthy ranges shifting upward with age. Below 5 percent for men or 13 percent for women risks hormonal and organ dysfunction.
How accurate is the Navy method?+
Usually within 3 to 4 percentage points of a DEXA scan when measurements are taken carefully. That is ample for tracking change over time, though not a substitute for clinical body composition analysis.
Why is body fat percentage better than BMI?+
Because it distinguishes fat from muscle. Two people with identical BMI can have very different body fat percentages, and it is the fat mass, particularly around the abdomen, that drives metabolic risk.
How do I measure my waist correctly?+
At the narrowest point for women and at navel level for men, with the tape horizontal and snug but not compressing the skin. Breathe out normally and do not pull it in.