BMI Calculator
Body Mass Index, category & healthy range
How to Use
- 1Choose Metric (cm/kg) or Imperial (ft, in / lb).
- 2Enter your height and weight and the BMI updates instantly.
- 3Read your category and the healthy weight range for your height.
- 4Check the calculation box to see exactly how it was worked out.
BMI Categories
- UnderweightBMI below 18.5
- Normal weightBMI 18.5 to 24.9
- OverweightBMI 25 to 29.9
- ObeseBMI 30 and above
Quick Examples
Tap an example to load it above.
Everything about the BMI Calculator
What BMI means, how it is calculated and how to read your result.
Body Mass Index (BMI) is a simple screening number that relates your weight to your height. It gives a quick indication of whether your weight is in a range generally considered healthy. This BMI calculator works in metric and imperial units, shows your category instantly and tells you the healthy weight range for your height.
Doctors, fitness apps and insurance forms all use BMI as a first check because it needs only two measurements. It's a great starting point for tracking your health over time, before and after a diet, a new exercise routine, or simply year to year.
Tip: BMI is a screening tool, not a diagnosis. Muscular athletes can have a high BMI with little body fat, and it reads differently for children, the elderly and during pregnancy. Use it as a guide and talk to a doctor for a full picture.
How BMI is calculated
The metric formula is BMI = weight (kg) ÷ height² (m²). For example, 70 kg at 1.75 m is 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 ≈ 22.9. In imperial units the formula is BMI = 703 × weight (lb) ÷ height² (in²).
BMI categories (WHO, adults)
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obese |
How to use this calculator
- 1Pick your units
Use the Metric tab for centimetres and kilograms, or Imperial for feet, inches and pounds.
- 2Enter height and weight
Type your measurements and the result appears as you type, with no button needed.
- 3Read your BMI and category
The purple display shows your BMI with a colour-coded category label.
- 4Check your healthy range
The tiles below show the healthy weight range for your height, and how far you are from it.
Frequently Asked Questions
What is a healthy BMI?
For most adults a BMI between 18.5 and 24.9 is considered the healthy range. Below 18.5 is classed as underweight, 25 to 29.9 as overweight, and 30 or above as obese. These are the standard World Health Organization categories.
How do I calculate BMI by hand?
Divide your weight in kilograms by your height in metres squared: BMI = kg ÷ m². For example, 70 kg ÷ (1.75 m × 1.75 m) ≈ 22.9. In pounds and inches, multiply your weight by 703 and divide by your height in inches squared.
Is BMI accurate for everyone?
No. BMI does not distinguish muscle from fat. Athletes and very muscular people may show as overweight while being lean, and it is interpreted differently for children, teens, the elderly and during pregnancy. Treat it as a quick screening number, not a medical diagnosis.
What is the healthy weight for my height?
This calculator shows it automatically: it multiplies 18.5 and 24.9 by your height in metres squared to give the low and high ends of the healthy range. For 175 cm that works out to roughly 56.7 to 76.3 kg.
How can I improve my BMI?
Gradual, sustainable changes work best: a balanced diet with a modest calorie adjustment, regular activity (the WHO suggests at least 150 minutes of moderate exercise a week), good sleep and consistency. Aim for slow progress of about 0.25 to 0.5 kg per week and consult a professional before major changes.
Is this BMI calculator free and does it work on mobile?
Yes. It's 100% free, needs no sign-up and no download. It works in any modern browser and is fully responsive. Your measurements stay in your browser; nothing is stored or shared.