BMI Calculator – Body Mass Index
Use this free BMI calculator to quickly estimate your Body Mass Index from your height and weight. Supports both metric and imperial units with instant results and health category.
Updated: November 2025 • For adults 18+ • Educational use only
What is BMI (Body Mass Index)?
Body Mass Index (BMI) is a simple screening tool that uses your height and weight to estimate whether you are underweight, in a healthy range, overweight or obese. It does not measure body fat directly, but it is widely used as a quick, general guide for adults.
BMI Categories for Adults
The table below shows the general BMI ranges used for adults aged 18 and above:
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
How to Use the DevineTools BMI Calculator
- Select your preferred unit system: Metric or Imperial.
- Enter your weight in kilograms or pounds.
- Enter your height in centimeters or inches.
- Click the Calculate BMI button.
- View your BMI value and category, along with a short explanatory message.
Understanding Your BMI Result
A BMI in the “normal weight” range (18.5–24.9) is generally associated with the lowest risk for weight-related health problems. A lower or higher BMI can be a signal to talk with a healthcare professional about your diet, activity level and overall health.
Remember, BMI is only one indicator. It does not consider muscle mass, body composition, age differences, sex or ethnicity. Two people with the same BMI can still have different health profiles.
Limitations of BMI
- It does not separate muscle from fat – muscular people may have a high BMI but low body fat.
- It does not account for age, sex, ethnicity or body frame differences.
- It is not designed for children, pregnant people or very athletic individuals.
For a complete picture of health, BMI should be combined with other assessments such as waist measurement, blood tests and professional medical guidance.
Is This BMI Calculator Free and Safe to Use?
Yes. The DevineTools BMI calculator is completely free, requires no sign-up and runs in your browser. Your values are processed on the page only and are not stored or sent to a server.
Frequently Asked Questions
Is this BMI calculator accurate?
The calculations follow the standard BMI formulas used worldwide. However, the result is an estimate and should not replace professional medical evaluation.
Can I use this BMI calculator for children?
This tool is designed for adults aged 18 and above. Children and teenagers require age- and sex-specific growth charts. Please consult a healthcare professional for guidance in those cases.
Should I change my diet or medication based on my BMI?
Do not change any medication or treatment only based on BMI. Always speak to a qualified healthcare professional before making major health decisions.
How often should I check my BMI?
Many people check a few times per year or when their weight changes. Use BMI as a general guide rather than a daily target.
Disclaimer: This BMI calculator is for general educational purposes and should not be used for diagnosis or treatment. Always consult a doctor or healthcare professional for personalised advice.