Calculator Inputs
Use the form below to estimate body fat percentage, lean mass, fat mass, BMI, waist-to-height ratio, FFMI, and FMI.
Example Data Table
This example uses metric inputs for an adult male and blends both available estimation methods.
| Sex | Age | Weight | Height | Neck | Waist | Hip | Body Fat | Fat Mass | Lean Mass | BMI | WHtR |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Male | 35 | 82 kg | 178 cm | 39 cm | 92 cm | Not needed | 21.94% | 17.99 kg | 64.01 kg | 25.88 | 0.517 |
Formula Used
1) Body Mass Index: BMI = weight (kg) ÷ height² (m²).
2) BMI-based body fat estimate: Body Fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex = 1 for men and 0 for women.
3) Circumference body fat estimate for men: Body Fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76.
4) Circumference body fat estimate for women: Body Fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387.
5) Primary estimate: When both methods are available, the calculator averages them. If circumference data is missing, it uses the BMI-based estimate.
6) Fat mass: weight × body fat %.
7) Lean mass: weight − fat mass.
8) Fat Mass Index: fat mass (kg) ÷ height² (m²).
9) Fat-Free Mass Index: lean mass (kg) ÷ height² (m²).
10) Waist-to-height ratio: waist circumference ÷ height.
How to Use This Calculator
- Choose metric or imperial units before entering measurements.
- Select sex and enter your age.
- Provide current body weight and standing height.
- Enter neck and waist measurements for the circumference method.
- Enter hip circumference when using the female circumference method.
- Press Calculate Estimate to show results above the form.
- Review body fat percentage, fat mass, lean mass, BMI, FFMI, FMI, and waist-to-height ratio.
- Use the CSV or PDF buttons to save the result summary.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates body fat percentage, fat mass, lean mass, BMI, waist-to-height ratio, Fat Mass Index, and Fat-Free Mass Index from simple body measurements.
2. Why are two body fat methods shown?
The calculator compares a circumference method with a BMI-based method. Showing both helps you see whether your estimate stays consistent across different assumptions.
3. Why do I need age and sex?
The BMI-based estimate uses age and sex because body fat distribution changes across adulthood and differs statistically between men and women.
4. Why might smart scale results differ?
Smart scales often use bioelectrical impedance, hydration status, and device algorithms. This calculator uses anthropometric equations, so the estimate can differ meaningfully.
5. Can athletes use this tool?
Yes, but athletic or highly muscular bodies may not fit population-based equations perfectly. Use the result as a screening estimate, not a definitive assessment.
6. Why is hip circumference only needed for women here?
The selected circumference equation for women includes hip measurement, while the male version uses neck, waist, and height only.
7. What does the waist-to-height ratio mean?
It compares waist size with height. Higher values can indicate more central fat storage, which is often linked with higher cardiometabolic risk.
8. When should I use professional testing?
Use professional testing when you need higher accuracy, medical decision support, sports monitoring, or follow-up for obesity, muscle loss, or metabolic concerns.