BMI & Body
Fat Calculator
Calculate your Body Mass Index (BMI) and get an estimate of your body fat percentage using the accurate U.S. Navy Method or BMI-based formula. Understand where you stand in seconds.
What Is BMI & Why Does It Matter?
Body Mass Index (BMI) is a numerical value calculated from your height and weight. It’s used as a quick screening tool to categorise weight status and identify potential health risks associated with being underweight, overweight or obese.
BMI is calculated using a simple formula: BMI = weight (kg) ÷ height² (m²). While it’s a useful first indicator, BMI has well-documented limitations — it doesn’t directly measure body fat and can misclassify muscular individuals as overweight.
BMI doesn’t account for muscle mass, bone density, ethnicity or age. A muscular athlete can have a “overweight” BMI despite very low body fat. Always consider BMI alongside other measurements for a complete health picture.
BMI Categories (WHO Standards)
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Nutritional deficiency, immune weakness |
| 18.5 – 24.9 | Healthy Weight | Lowest risk for weight-related conditions |
| 25.0 – 29.9 | Overweight | Increased risk of heart disease, diabetes |
| 30.0 – 34.9 | Obese (Class I) | High risk — weight loss recommended |
| 35.0 – 39.9 | Obese (Class II) | Very high risk — medical attention advised |
| 40.0+ | Obese (Class III) | Extremely high risk — urgent intervention |
Body Fat Percentage: A Better Measure of Health
While BMI gives a rough idea of weight status, body fat percentage tells you what your body is actually made of. Two people can have the same BMI but very different body compositions — one muscular and lean, one carrying excess fat.
Body fat percentage is the proportion of your total body weight that is fat tissue. The remainder — muscle, bone, water, and organs — is your lean body mass.
Healthy Body Fat Ranges
| Category | Men | Women |
|---|---|---|
| Essential Fat | 2–5% | 10–13% |
| Athletic | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average / Acceptable | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
How the U.S. Navy Body Fat Method Works
Our calculator uses the U.S. Navy Circumference Method — one of the most accurate non-invasive body fat estimation formulas available. It uses body circumference measurements (neck, waist, and hip for women) alongside height.
- Men: Body Fat % = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
- Women: Body Fat % = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
Studies show this method has an error margin of approximately ±3–4% compared to DEXA scans, making it one of the best free estimation tools available outside of a clinical setting.
How to Take Accurate Body Measurements
- Use a flexible fabric tape measure — rigid measuring tapes will give inaccurate results.
- Neck: Measure just below the larynx (Adam’s apple), with the tape perpendicular to the body’s axis.
- Waist: Measure at the level of the navel, while breathing normally. Don’t suck in or hold your breath.
- Hip (women only): Measure at the widest part of the hips and buttocks.
- Measure at the same time each day — morning before eating is most consistent.
- Take 2–3 measurements and use the average for the best accuracy.
Track your measurements monthly rather than weekly. Body composition changes slowly, and daily fluctuations in hydration and food intake can cause misleading short-term variation.