How to use the BMI calculator
- Choose metric (centimetres and kilograms) or imperial (feet, inches and pounds).
- Enter your height and weight.
- Read your BMI, its category and the healthy weight range for your height. Tick Asian cut-offs if you are of South Asian or East Asian descent (see below).
What is BMI?
Body Mass Index is a simple number that compares your weight with your height. It was devised by the Belgian statistician Adolphe Quetelet in the 1830s and is used by the World Health Organization (WHO) and doctors worldwide as a quick screening tool for weight categories in adults.
BMI = weight (kg) ÷ height (m)²
BMI = 703 × weight (lb) ÷ height (in)²
Example: someone 1.70 m tall weighing 68 kg has a BMI of 68 ÷ (1.70 × 1.70) = 23.5.
BMI categories for adults
| BMI | WHO category | Asian cut-off (WHO expert consultation) |
|---|---|---|
| Below 18.5 | Underweight | Underweight |
| 18.5 – 24.9 | Healthy weight | Healthy: 18.5 – 22.9 |
| 25.0 – 29.9 | Overweight | Increased risk: 23.0 – 27.4 |
| 30.0 and above | Obesity | High risk: 27.5 and above |
Why there are Asian cut-offs
Research summarised by a WHO expert consultation (2004) found that many Asian populations — including people from Bangladesh, India, Pakistan, China and Japan — tend to have a higher risk of type 2 diabetes and heart disease at a lower BMI than European populations. For that reason, health services in several countries, including the UK’s NICE guidance, use lower action points of 23 and 27.5 for people of South Asian, Chinese and other Asian backgrounds.
Healthy weight range for your height
The calculator also works backwards: it shows the weight range that would give a BMI between 18.5 and 24.9 (or 22.9 with Asian cut-offs) for your height. This is often more useful than the BMI number itself when you are setting a goal.
Limitations of BMI
BMI is quick and useful for populations, but it is not a diagnosis for an individual:
- Muscle weighs more than fat. Athletes and very muscular people can have a high BMI while carrying little body fat.
- It ignores where fat is stored. Fat around the waist is linked to higher health risk. Measuring waist circumference alongside BMI gives a better picture — a waist measurement of more than half your height is a common warning sign.
- Age and sex. Older adults naturally lose muscle, and women generally have more body fat than men at the same BMI.
- Children and teenagers need age- and sex-specific BMI percentiles, not the adult categories used here.
- Pregnancy makes BMI unsuitable.
If your result worries you, speak to a doctor or registered dietitian, who can consider your full health picture.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI from 18.5 to 24.9 is classed as a healthy weight by the WHO. For people of Asian descent, a range of 18.5 to 22.9 is often recommended.
Is BMI accurate?
BMI is a useful screening tool but not a direct measure of body fat. It can overestimate fat in muscular people and underestimate it in older adults. Waist measurement and a doctor’s assessment give a fuller picture.
Can I use this BMI calculator for children?
No. Children and teenagers (under 20) should use age- and sex-specific BMI percentile charts, which this calculator does not provide.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. Or select “Imperial” above and the calculator does it for you.
Are my measurements stored?
No. Your height and weight are only used in your browser to calculate the result and are not saved or sent anywhere.