BMI Calculator
CalcTools AI's BMI Calculator is an intelligent tool designed to help you quickly assess your body mass index. By entering your weight and height, our calculator delivers an accurate result and our integrated AI assistant explains exactly what your BMI category means for your health.
Whether you are tracking a fitness journey, monitoring your health, or simply curious, our tool provides fast, reliable, and easy-to-understand results. Download a detailed PDF report to share with a health professional or keep for your records.
How to Use the BMI Calculator
- Select your gender — male or female. Gender informs the AI narrative about your result.
- Enter your weight — choose kilograms (kg) or pounds (lbs).
- Enter your height — choose feet & inches (imperial) or centimetres (metric).
- Click "Calculate BMI" — your result appears instantly below the form.
- Click "Explain with AI" — the AI analyses your category and gives personalised health context.
- Optionally download a PDF report for your records.
BMI Formula
$$\text{BMI} = \frac{\text{weight (kg)}}{\text{height (m)}^2}$$
For imperial inputs, feet and inches are first converted to metres before applying the formula.
BMI Categories
| BMI Range | Category |
|---|---|
| < 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| ≥ 30.0 | Obese |
These thresholds are defined by the World Health Organisation (WHO) and apply to most adults aged 18–65. They should be interpreted alongside other health indicators.
Limitations of BMI
BMI is a simple screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age-specific differences, or ethnic background. Athletes with high muscle mass may register as "overweight" despite being healthy. Always consult a qualified health professional for a full assessment.