BMI Calculator
Calculate your Body Mass Index instantly. Supports metric (kg/cm) and imperial (lbs/in). Results include your BMI category, healthy weight range, and a visual BMI scale.
📋 WHO BMI Classification — Where You Stand
| Category | BMI Range | Health Risk | Weight Range (you) |
|---|---|---|---|
| Severe Underweight | < 16.0 | Very High (medical risk) | 0–49 kg |
| Moderate Underweight | 16.0 – 16.9 | High | 49–52 kg |
| Mild Underweight | 17.0 – 18.4 | Moderate | 52–57 kg |
| ▶ Normal Weight | 18.5 – 24.9 | Low (optimal) | 57–77 kg |
| Overweight | 25.0 – 29.9 | Increased | 77–92 kg |
| Obese Class I | 30.0 – 34.9 | High | 92–107 kg |
| Obese Class II | 35.0 – 39.9 | Very High | 107–123 kg |
| Obese Class III | ≥ 40.0 | Extremely High | 123–+ kg |
💡 Understanding Your Result
- Your BMI of 22.9 falls in the Normal Weight category (18.5 – 24.9). For your height, a healthy weight range is 57–76 kg.
- BMI has limitations: it does not directly measure body fat and does not account for muscle mass, bone density, age, sex, or ethnicity. Athletes and highly muscular individuals may be classified as overweight despite low body fat. Asian populations may have higher health risks at lower BMI thresholds (23–25).
- Consult a healthcare provider for a complete health assessment. BMI is a screening tool only. A physician can evaluate body composition, metabolic health markers (blood glucose, cholesterol, blood pressure), and create an appropriate health plan.
How to Use This Tool
- Step 1: Choose your unit system
Select "Metric" if you know your measurements in kilograms and centimetres, or "Imperial" if you use pounds and inches. The calculator switches inputs automatically.
- Step 2: Enter your weight
Type your current weight. For metric use kilograms (e.g. 70 kg); for imperial use pounds (e.g. 154 lb). Use your weight without clothing for the most accurate result.
- Step 3: Enter your height
Type your height in centimetres (metric) or feet and inches (imperial). Measure yourself standing upright against a wall, barefoot, for best accuracy.
- Step 4: Read your results
The calculator instantly shows your BMI number, weight category (Underweight / Normal / Overweight / Obese), your healthy weight range for your height, and a visual BMI scale so you can see where you sit.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is a simple screening number calculated from an adult’s weight and height. First described by Belgian mathematician Adolphe Quetelet in the 19th century (then called the Quetelet Index), it was adopted by the World Health Organization as a global standard for classifying weight status in 1995. Today it is used in clinical practice in over 190 countries as a first-line obesity screening tool.
The appeal of BMI is its simplicity: you only need two measurements — weight and height — and the math is straightforward. For population-level analysis, BMI correlates well with more precise body-fat measurements such as dual-energy X-ray absorptiometry (DEXA). At the individual level, however, it has important limitations (see FAQ below).
Our calculator uses the exact same WHO formula that clinicians use. Results are instant, no account required, and no data is stored or transmitted — all calculations happen in your browser.
The Formula & Method
Metric: BMI = weight (kg) ÷ height (m)² Imperial: BMI = [weight (lb) × 703] ÷ height (in)²
"Weight" is your body mass in kilograms or pounds. "Height" in the metric formula must be in metres (not centimetres) — convert by dividing cm by 100. The constant 703 in the imperial formula adjusts for the unit conversion from lb/in² to kg/m².
Worked Example
Scenario: A 35-year-old woman who weighs 68 kg and is 165 cm tall wants to check her BMI.
| Input | Value |
|---|---|
| Weight | 68 kg |
| Height | 165 cm = 1.65 m |
| Height squared | 1.65² = 2.7225 m² |
A BMI of 24.98 sits right at the upper edge of the Normal range. The calculator also shows her healthy weight range: approximately 50.3 kg to 67.4 kg for her height. She is within range, though close to the Overweight boundary — a good result to discuss with her GP at her next routine check-up.
Common Mistakes to Avoid
Mistake: Entering height in feet directly into the centimetre field.
Fix: Switch the unit toggle to Imperial before entering feet/inches, or convert: 5 ft 9 in = 175.3 cm.
Mistake: Using weight with clothes and shoes on.
Fix: Weigh yourself barefoot, in light clothing or none, ideally in the morning before eating.
Mistake: Treating BMI as the only health indicator.
Fix: Pair BMI with waist circumference, blood pressure, cholesterol, and a conversation with your doctor for a complete picture.
Mistake: Applying adult BMI charts to children and teenagers.
Fix: Children need age- and sex-specific BMI percentile charts (CDC or WHO). Use a dedicated child BMI calculator instead.
Frequently Asked Questions
Related Calculators
💡 Pro Tips
BMI does not distinguish between muscle and fat. Athletes and bodybuilders often register as "overweight" despite having very low body fat. Use BMI alongside body fat percentage and waist circumference for a complete picture.
BMI thresholds were established for European populations. Many clinicians use lower BMI cutoffs for Asian adults (≥23 for overweight, ≥27.5 for obese) because health risks appear at lower BMI values.
Waist circumference is often a better predictor of metabolic health risk than BMI. A waist over 35 inches (89 cm) for women or 40 inches (102 cm) for men signals elevated cardiovascular risk regardless of BMI score.
Track your BMI trend over months rather than as a single snapshot. A consistent downward trend matters far more than hitting a specific number on any given day — focus on the trajectory.
When to Use This Calculator
Calculate your BMI as part of your annual self-assessment alongside blood pressure and cholesterol.
Find the BMI-normal weight range for your height to set a realistic, medically-recognised target weight.
Check BMI is in the healthy range before trying to conceive — optimal BMI reduces pregnancy complications.
Monitor BMI monthly during a training program to separate scale weight changes from body composition changes.
Calculate in advance to have an informed conversation about weight and health with your healthcare provider.
Medical Disclaimer
BMI Calculator — Results are based on the WHO BMI formula and standard classification categories. BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, fat distribution, age, sex, or ethnicity. A BMI result outside the normal range should be discussed with a qualified healthcare provider who can assess your full health picture before drawing clinical conclusions or making health decisions.
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