BMI Calculator

The BMI Calculator estimates Body Mass Index (BMI) from height and weight. BMI is a screening number that compares weight to height. It does not diagnose health on its own. Use it as a starting point, alongside other information from a health professional.

What Is BMI Calculator

The BMI Calculator takes a height and a weight and returns a BMI value and a weight category. It uses the standard adult BMI formula. It works in the browser, so you can check a value quickly and repeat the calculation with different inputs.

BMI Formula

BMI = weight (kg) / height (m)^2

Height must be in metres. If you enter height in centimetres, divide by 100 first. For example, 175 cm is 1.75 m. Weight must be in kilograms. If you use pounds and feet/inches, the workspace unit controls convert the entries before the calculation.

How to Use

1. Enter your height in the height field. Choose cm or ft/in.
2. Enter your weight in the weight field. Choose kg or lbs.
3. Click Process to calculate.
4. Read the BMI value and the category shown in the result.
5. Change either input and calculate again to compare values.

Worked Example

Input: 70 kg and 175 cm.

Convert height: 175 cm = 1.75 m. Then 70 kg / 175 cm → 70 / (1.75^2) = 22.9 → Normal range.

Calculation: 1.75^2 = 3.0625, and 70 / 3.0625 = 22.857, which rounds to 22.9. The result falls in the Normal range in the table below.

WHO Categories

These are the World Health Organization (WHO) adult categories. They are screening bands, not a diagnosis.

Limitations

• BMI does not measure body fat, muscle, bone density, or fat distribution.
• A muscular person can have a high BMI without excess body fat, because muscle weighs more than fat for the same volume.
• BMI does not reflect bone density, age-related muscle loss, or where fat is carried.
• For athletes, BMI can overstate risk. For pregnancy, BMI alone is not a suitable guide, because weight changes during pregnancy are expected.
• For older adults, BMI can understate risk when muscle loss is present, even if weight looks stable.
• WHO categories are intended for adults. They do not apply in the same way to children and adolescents, who are assessed with age- and sex-specific growth charts.
• Small entry errors matter. Check the height and weight units before calculating, because a wrong unit changes the result.

Frequently Asked Questions

What is a healthy BMI?

For adults, the WHO Normal band is 18.5–24.9. A value in that band is a screening result, not a guarantee of health. Other factors, such as diet, activity, blood pressure, and family history, also matter.

Can I use imperial units?

Yes. The workspace offers ft/in for height and lbs for weight. Enter the values in the units shown, and check that the correct unit is selected before calculating.

Does BMI work for athletes?

Not always. Athletes with high muscle mass can have a high BMI without excess body fat. In that case, BMI should be read alongside body composition and other measures, not on its own.

Should I act on a BMI result alone?

No. BMI is a screening tool. If a result is outside the Normal band, or if you have symptoms or health concerns, speak to a health professional before changing diet, activity, or treatment.

Disclaimer

This tool provides general information only, not medical advice. It does not replace professional assessment, diagnosis, or treatment. If you have questions about your health, seek advice from a qualified health professional.