Body Fat Calculator
This body fat calculator estimates your body fat percentage from weight, height, age, and sex. It first calculates your BMI, then applies the Deurenberg formula to convert that number into an estimated body fat percentage. The result is a quick reference figure, not a lab measurement, so it works best alongside other tracking methods rather than as a standalone diagnosis.
Quick answer
Body fat percentage is estimated from BMI, age, and sex using the Deurenberg formula.
What this tells you
- •Body fat percentage is estimated from BMI, age, and sex using the Deurenberg formula.
- •The calculator first works out BMI from your weight and height, then adjusts that figure for age and sex.
- •This is a population-based estimate, not a direct measurement of fat mass.
- •Results are most useful when tracked over time rather than judged from a single reading.
- •Athletes and people with high muscle mass may see estimates that read higher than their actual body fat.
How to Use
- 1Enter your weight in kilograms.
- 2Enter your height in centimeters.
- 3Enter your age in years.
- 4Select your sex (male or female), since the formula applies a different adjustment for each.
- 5Select Calculate to see your estimated body fat percentage and BMI.
How It Works
Formula
Body Fat % = 1.20 × BMI + 0.23 × Age − 10.8 × Sex − 5.4
(Sex = 1 for male, 0 for female. BMI = weight in kg ÷ (height in m)²)This is the Deurenberg formula, a widely cited equation that estimates body fat percentage from BMI rather than from skinfold thickness or bioelectrical signals. The calculator first computes BMI from your weight and height, then multiplies that number by 1.20 and adds a small upward adjustment for age (0.23 points per year). It then applies a downward adjustment for male sex (10.8 points, since men typically carry a lower body fat percentage than women at the same BMI) and subtracts a constant of 5.4. Because the formula relies on BMI, it inherits BMI's main weakness: it cannot tell the difference between muscle and fat, so it estimates body composition indirectly rather than measuring it.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Adult male, average build
BMI = 70 ÷ (1.75 × 1.75) = 22.9. Body fat % = (1.20 × 22.9) + (0.23 × 30) − (10.8 × 1) − 5.4 = 27.4 + 6.9 − 10.8 − 5.4 = 18.1%. This falls in a typical healthy range for an adult male of this age.
Adult female, average build
BMI = 60 ÷ (1.65 × 1.65) = 22.0. Body fat % = (1.20 × 22.0) + (0.23 × 28) − 0 − 5.4 = 26.4 + 6.4 − 5.4 = 27.5%. The estimate is higher than the male example at a similar BMI, because the formula does not subtract the 10.8-point male adjustment for female inputs.
Older male, higher BMI
BMI = 85 ÷ (1.80 × 1.80) = 26.2. Body fat % = (1.20 × 26.2) + (0.23 × 50) − 10.8 − 5.4 = 31.5 + 11.5 − 10.8 − 5.4 = 26.8%. Both the higher BMI and the higher age push the estimate up compared with the first example.
Younger female, lower BMI
BMI = 50 ÷ (1.60 × 1.60) = 19.5. Body fat % = (1.20 × 19.5) + (0.23 × 22) − 0 − 5.4 = 23.4 + 5.1 − 5.4 = 23.1%. Even at a lower BMI, the estimate stays a fair distance above the male examples because of how the formula treats sex.
Active male, higher weight
BMI = 95 ÷ (1.85 × 1.85) = 27.8. Body fat % = (1.20 × 27.8) + (0.23 × 35) − 10.8 − 5.4 = 33.3 + 8.1 − 10.8 − 5.4 = 25.2%. If most of that weight is muscle rather than fat, this estimate can read higher than a direct measurement such as a DEXA scan would show.
Common mistakes
- Entering pounds in the weight field when the calculator expects kilograms, which throws off both BMI and the body fat estimate.
- Mixing up height units, such as entering total inches as centimeters.
- Treating the result as a clinical diagnosis rather than a general estimate.
- Comparing this formula's output directly against a caliper, DEXA scan, or bioelectrical impedance reading, which can use different methods and give different numbers.
- Expecting the estimate to shift meaningfully from small day-to-day changes in weight, when body composition typically changes gradually over weeks or months.
- Ignoring that the formula was built from population averages, so it can be less accurate for athletes, older adults, or people outside typical body proportions.
Limitations
This calculator estimates body fat percentage using the Deurenberg formula, which is based on BMI, age, and sex rather than a direct measurement of fat mass. Because it relies on BMI, it cannot distinguish muscle from fat, so it tends to overestimate body fat in muscular or highly active people and can be less precise for older adults, pregnant people, or those with atypical body proportions. Results may differ meaningfully from skinfold calipers, bioelectrical impedance scales, or DEXA scans, since each method measures body composition differently. Use this estimate as a general reference point, not a substitute for a direct assessment.
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