Body Fat Percentage Calculator
No tape measure handy? Enter your age, sex, height and weight and we estimate body fat from your BMI.
This calculator gives general estimates for information only. It is not medical advice and does not replace a consultation with a doctor or other qualified health professional.
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The formula
Body fat % = 1.20 x BMI + 0.23 x age - 10.8 x (1 for men, 0 for women) - 5.4
What this estimate is
The Deurenberg equation links BMI and age to body fat percentage. It is quick and uses only numbers most people know, but it is less accurate than measuring, especially for athletes and older adults.
Worked example
A 30 year old man with a BMI of 24.7 (80 kg at 180 cm): 1.2 x 24.7 + 0.23 x 30 - 10.8 - 5.4 = 20.3 percent. That puts him in the average range, with about 16.3 kg of fat and 63.7 kg of lean mass.
For a better estimate
Try the Navy tape method, or a DEXA scan or a good bioimpedance scale. Measuring the same way each time matters more than which method you pick.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Male; Age (years): 30; Height (cm): 180; Weight (kg): 80 | Estimated body fat: 20.3% |
| Female; Age (years): 35; Height (cm): 165; Weight (kg): 65 | Estimated body fat: 31.3% |
Body Fat Percentage Calculator: frequently asked questions
How accurate is a tape measure estimate?
The Navy method is typically within 3 to 4 percentage points of a DEXA scan for most people. It is better for tracking change over time than for a single exact figure, so measure the same way each time.
Where exactly should I measure?
Neck just below the larynx, waist at the navel (relaxed, not sucked in), and hips at the widest point. Keep the tape snug but not tight, and measure three times to average.
Can I rely on this result as medical advice?
No. It is a general estimate for information only. It cannot replace a check-up, and your doctor can interpret the numbers for your own situation.
Is what I enter in this calculator saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this calculator free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026