BMI Calculator
Calculate your Body Mass Index using height and weight to check whether your weight falls within a healthy range.
What Is a BMI Calculator?
A BMI calculator estimates your Body Mass Index using your height and weight. BMI is a screening tool that categorizes weight relative to height, helping identify whether an adult's weight falls within underweight, healthy, overweight, or obese ranges. It is widely used by healthcare professionals as a starting point for assessing body fat and related health risks.
How BMI Is Calculated
BMI is derived from a straightforward formula using metric or imperial measurements.
Metric Formula
BMI = weight (kg) ÷ height (m)²
Imperial Formula
BMI = (weight (lbs) ÷ height (in)²) × 703
The result is a single number that corresponds to a weight category. The calculation assumes a direct relationship between weight and height squared, which works well for most adults but has known limitations.
How to Use This BMI Calculator
- Enter your height — select either feet/inches or centimeters.
- Enter your weight — select either pounds or kilograms.
- Click "Calculate" — your BMI and weight category will display instantly.
No registration or personal data is required. The calculation happens entirely in your browser.
Understanding Your BMI Result
BMI results fall into standard categories established by the World Health Organization:
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
These ranges apply to most adults aged 18–65. A higher BMI often correlates with increased risk for conditions such as heart disease, type 2 diabetes, and hypertension. A lower BMI may indicate nutritional deficiencies or other health concerns.
Common Mistakes When Using BMI
- Using incorrect units — mixing metric and imperial values produces an inaccurate result. Always double-check your unit selection.
- Misinterpreting the category — BMI is a screening tool, not a diagnostic test. A "healthy" BMI does not guarantee good health, and an "overweight" BMI does not automatically mean poor health.
- Applying BMI to children — BMI for children uses age- and sex-specific percentiles, not the adult categories shown here.
Limitations of BMI
BMI does not measure body fat directly. It cannot distinguish between muscle mass and fat mass. This means:
- Athletes and bodybuilders with high muscle mass may be classified as overweight or obese despite having low body fat.
- Older adults who have lost muscle may have a healthy BMI but carry excess body fat.
- BMI does not account for fat distribution, which is an independent health risk factor.
For a more complete picture, consider additional measurements such as waist circumference, body fat percentage, or a consultation with a healthcare provider.
Practical Use Cases
- Health screening — quickly assess whether your weight falls within a typical healthy range.
- Weight tracking — monitor BMI changes over time alongside other health metrics.
- Fitness goal setting — use BMI as one data point when planning weight loss or muscle gain targets.
- Medical consultations — provide your BMI to a doctor as part of a broader health discussion.
FAQ
Is BMI accurate for everyone?
No. BMI is a general screening tool, not a precise diagnostic measure. It is less accurate for athletes, pregnant women, older adults, and people with high muscle mass. Always interpret BMI alongside other health indicators.
What is a healthy BMI for my age?
For adults aged 18–65, the same BMI categories apply regardless of age. For children and teenagers, BMI is evaluated using age- and sex-specific percentiles. Older adults may have different body composition, so BMI should be interpreted with caution.
Can I use BMI to measure body fat?
BMI estimates body fat indirectly based on height and weight. It does not measure body fat directly. For a direct measurement, methods such as skinfold calipers, bioelectrical impedance, or DEXA scans are more accurate.
What should I do if my BMI is high?
A high BMI is a signal to discuss your health with a doctor. They can assess additional factors such as diet, physical activity, family history, and other lab results. Do not rely on BMI alone to make health decisions.