BMI Calculator vs Body Fat Calculator
Both tools are 100% free, browser-based, and require no signup. Here is how they differ so you can pick the right one for your task.
BMI Calculator
Free BMI calculator. Enter weight and height in metric or imperial to get your BMI, WHO category, BMI Prime, and healthy weight range for your height. No signup.
Use BMI Calculator →Body Fat Calculator
Free body fat percentage calculator. Uses 3 methods side-by-side: the US Navy formula, a BMI-based estimate, and a skinfold-based estimate — with confidence ranges for each. No signup.
Use Body Fat Calculator →Feature Comparison
| Feature | BMI Calculator | Body Fat Calculator |
|---|---|---|
| Metric (kg/cm) and imperial (lb/ft+in) with one-click toggle | ✓ | — |
| WHO BMI category: Underweight, Normal, Overweight, Obese class I/II/III | ✓ | — |
| BMI Prime — your ratio to the upper-normal limit of 25 | ✓ | — |
| Healthy weight range for your exact height | ✓ | — |
| Visual category bar showing where you fall | ✓ | — |
| Shareable URL with preset inputs | ✓ | — |
| 100% browser-based — no data sent to any server | ✓ | — |
| US Navy circumference method (neck, waist, hip) | — | ✓ |
| BMI-based body fat estimate (Deurenberg formula) | — | ✓ |
| Skinfold method explanation with confidence context | — | ✓ |
| All 3 methods shown side-by-side with confidence ranges | — | ✓ |
| Body fat category ratings (essential, athletic, fitness, average, obese) | — | ✓ |
| Metric and imperial inputs | — | ✓ |
| 100% browser-based — no data sent anywhere | — | ✓ |
| 100% free — no signup, no watermarks | ✓ | ✓ |
| Browser-based — files never uploaded | ✓ | ✓ |
When to Use Each Tool
- →Select Metric (kg/cm) or Imperial (lb/ft+in) using the toggle at the top.
- →Type your weight in kilograms (metric) or pounds (imperial).
- →Enter your height in centimeters (metric) or feet and inches (imperial).
- →Input neck, waist, and (if female) hip circumferences. Choose metric (cm) or imperial (inches).
- →These are needed for the BMI-based method and to display lean mass.
- →See the Navy, BMI-based, and skinfold method results side-by-side with their confidence ranges.
Frequently Asked Questions
The World Health Organization defines a healthy BMI as 18.5 to 24.9. Below 18.5 is considered underweight, 25–29.9 is overweight, and 30 or above is obese. These ranges apply to most adults aged 18–65.
BMI is a useful population-level screening tool but has well-known limitations. It cannot distinguish fat mass from lean mass, so muscular athletes often register as "overweight" despite having very low body fat. It also does not account for fat distribution — abdominal (visceral) fat carries higher health risk than fat elsewhere. Use BMI as one data point alongside waist circumference, body fat percentage, and a conversation with your doctor.
The US Navy circumference method estimates body fat using neck, waist, and (for women) hip measurements. For men: %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. For women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. It typically estimates within ±3–4% of DEXA scan results.
DEXA (dual-energy X-ray absorptiometry) and hydrostatic weighing are the gold standards but require specialized equipment. Among field methods, the Navy circumference method is practical and reasonably accurate (±3–4%). Skinfold calipers with a trained technician are also reliable (±3%). BMI-based estimates are least accurate at the individual level but require no measurements beyond weight and height. No formula replaces a direct measurement.
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