BMI Calculator
Calculate your body mass index in metric or imperial units. See your category under WHO, Asian or Indian ranges, your healthy weight range and your waist-to-height ratio.
- Instant results
- WHO, Asian & Indian ranges
- Waist-to-height ratio
- Nothing stored
Calculated on your device. Nothing is stored or uploaded.
Enter your height and weight
Your BMI, category and healthy weight range appear here instantly.
How to use the BMI calculator
- Enter height and weightUse centimetres and kilograms, or switch to feet, inches and pounds. Your BMI updates as you type.
- Choose the category standardKeep the international WHO ranges, or use the lower Asian or Indian cut-offs that better reflect risk for South and East Asian people.
- Add waist and age (optional)Your waist gives the waist-to-height ratio. Your age tells the calculator whether adult categories apply.
BMI categories for adults
Body mass index is your weight in kilograms divided by your height in metres squared (kg/m²). It is a quick screening measure used by doctors and public health bodies worldwide. These ranges apply to adults aged 20 and over.
| Category | WHO (international) | Asian (WHO 2004) | India (2009) |
|---|---|---|---|
| Underweight | below 18.5 | below 18.5 | below 18.0 |
| Healthy weight | 18.5 – 24.9 | 18.5 – 22.9 | 18.0 – 22.9 |
| Overweight | 25.0 – 29.9 | 23.0 – 27.4 | 23.0 – 24.9 |
| Obesity | 30.0 and above class I 30–34.9 · II 35–39.9 · III 40+ | 27.5 and above | 25.0 and above |
The formula
Metric: BMI = weight (kg) ÷ height (m)². Example: 70 kg ÷ (1.75 × 1.75) = 22.9.
Imperial: BMI = 703 × weight (lb) ÷ height (in)². Example: 703 × 154 ÷ (69 × 69) = 22.7.
Why BMI isn’t the whole story
- Muscle vs fat: BMI counts all weight the same, so very muscular people can show as overweight.
- Where fat sits: fat around the waist carries more health risk than fat elsewhere. That’s why the waist-to-height ratio is shown when you enter your waist.
- Age and background: older adults and people of Asian descent can have higher health risks at a “normal” BMI.
- Pregnancy and children: adult categories don’t apply. Children are assessed with age- and sex-specific growth charts.
Other measures shown
BMI Prime is your BMI divided by 25, the top of the WHO healthy range – 1.00 means you are exactly at the upper limit. The Ponderal Index divides weight by height cubed, which is less skewed for very tall or short people. The “new BMI”, proposed by Oxford mathematician Nick Trefethen, uses 1.3 × weight ÷ height2.5 for the same reason. These are for interest; doctors use standard BMI.
This calculator is for general information and is not medical advice. Speak to a doctor or registered dietitian about your weight and health.
Frequently asked questions
What is a healthy BMI?
For most adults, the World Health Organization classes a BMI of 18.5 to 24.9 as a healthy weight, 25 to 29.9 as overweight and 30 or more as obesity. For people of Asian background, many health bodies use lower cut-offs because health risks rise at a lower BMI.
Why are the Asian and Indian BMI ranges lower?
Studies show that people of Asian descent tend to have more body fat and a higher risk of type 2 diabetes and heart disease at the same BMI. A 2004 WHO expert consultation suggested action points of 23 and 27.5 for Asian populations, and Indian guidelines from 2009 class 23–24.9 as overweight and 25 or more as obesity.
How do I calculate BMI myself?
Divide your weight in kilograms by your height in metres squared. For example, 70 kg ÷ (1.75 m × 1.75 m) = 22.9. In imperial units, multiply your weight in pounds by 703 and divide by your height in inches squared.
Is BMI accurate for athletes and older adults?
Not always. BMI can’t tell muscle from fat, so muscular people may show as overweight while being healthy, and older adults who have lost muscle may have a normal BMI with high body fat. Waist measurement and other checks help fill the gap.
What is a good waist-to-height ratio?
UK guidance from NICE recommends keeping your waist below half your height – a ratio under 0.5. A ratio of 0.5 to 0.59 indicates increased health risk, and 0.6 or more indicates high risk. Measure around your waist halfway between your lowest rib and the top of your hips.
Can I use this BMI calculator for children?
The calculator shows the BMI number, but adult categories don’t apply to anyone under 20. Children’s BMI is judged with growth charts that compare them with others of the same age and sex. A doctor can interpret it properly.
Does BMI apply during pregnancy?
No. Weight gain during pregnancy is expected, so BMI categories don’t apply. Doctors use your pre-pregnancy BMI to guide how much weight gain is healthy.
Is my data saved?
No. Everything is calculated in your browser and nothing is stored or sent anywhere. A link to your result is only created if you click “Copy link”.
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