A clear, accurate BMI calculator for adults
This BMI calculator works out your body mass index from your height and weight and tells you which category you fall into, using either the standard World Health Organization (WHO) cut-offs or the lower Asian cut-offs recommended for people of South Asian, East Asian and Southeast Asian descent. Enter centimetres and kilograms, or feet, inches and pounds — the tool remembers which you prefer.
Alongside the number you get a colour-coded scale, the exact weight range that counts as healthy for your height, how far you are from that range, your BMI Prime and your ponderal index. Everything is calculated in your browser, so your measurements are never sent anywhere.
BMI is a screening number, not a diagnosis. Results are estimates for healthy adults, not medical advice; a doctor can weigh them against your waist size, blood pressure and blood tests.
How to use the BMI Calculator
- Choose Metric (cm, kg) or Imperial (ft, in, lb). Switching converts the numbers you have already typed.
- Enter your height and your weight. Weigh yourself in the morning in light clothing for the most consistent result.
- Tick Use Asian cut-offs if you are of Asian ethnicity — common for readers in India, Pakistan, Bangladesh, China and Southeast Asia.
- Read your BMI and category in the result panel and see where the marker sits on the scale.
- Check the healthy weight range for your height and the table showing every category in your own units.
BMI Calculator features
WHO and Asian categories
Switch between the six WHO adult classes and the Asian action points of 23 and 27.5 with one tick.
Healthy weight for your height
Shows the weight range that gives a BMI of 18.5 to 24.9 (or 22.9 with Asian cut-offs) and how much to gain or lose to reach it.
Visual BMI scale
A colour-coded gauge with a marker shows how close you are to the next category; every colour is also labelled in words.
BMI Prime and ponderal index
Two extra ratios: BMI Prime compares you with the upper healthy limit, and the ponderal index divides by height cubed, which suits very tall or very short people better.
Formula shown with your numbers
The exact calculation is printed under the result, so you can check it by hand.
Private, remembers your units
Nothing leaves your device; your unit choice is saved in your browser.
How BMI is calculated
Body mass index was devised by the Belgian statistician Adolphe Quetelet in the 1830s and named by physiologist Ancel Keys in 1972. The formula is simply weight in kilograms divided by height in metres squared: BMI = kg ÷ m². In imperial units it is 703 × weight in pounds ÷ height in inches squared.
Worked example: someone 175 cm tall weighing 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9, which is in the normal range. In imperial, 5 ft 9 in (69 in) and 160 lb gives 703 × 160 ÷ 4,761 = 23.6.
BMI Prime is your BMI divided by the upper limit of the healthy range (25, or 23 for Asian cut-offs). A value of 1.00 sits exactly on the limit; 0.74–0.99 is the healthy band. The ponderal index (also called Rohrer’s or the corpulence index) divides weight by height cubed, so it changes less with height than BMI does.
BMI categories for adults
The WHO classification applies to adults of all ages and both sexes. For Asian populations, a 2004 WHO expert consultation found that health risks such as type 2 diabetes and heart disease rise at lower BMIs, and suggested public-health action points of 23 and 27.5. India’s 2009 consensus guidelines go further and treat a BMI of 25 or more as obesity.
| Category | WHO BMI | Asian BMI |
|---|---|---|
| Underweight | Below 18.5 | Below 18.5 |
| Normal weight | 18.5 – 24.9 | 18.5 – 22.9 |
| Overweight / increased risk | 25.0 – 29.9 | 23.0 – 27.4 |
| Obesity class I | 30.0 – 34.9 | 27.5 and above |
| Obesity class II | 35.0 – 39.9 | — |
| Obesity class III | 40.0 and above | — |
What BMI can’t tell you
- Muscle vs fat: BMI cannot tell the difference. Rugby players, bodybuilders and many athletes are classed as overweight while carrying little fat. The body fat calculator gives a better picture.
- Older adults: muscle and bone are gradually lost with age, so an older person can have a “normal” BMI and still carry too much fat — or be frail at a BMI that looks fine on paper.
- Where fat sits: fat around the waist carries more risk than fat on the hips. Pair your BMI with a waist measurement or the waist-to-hip ratio calculator; a waist less than half your height is a useful rule of thumb.
- Children and teens: under 20, BMI is compared with growth charts for the same age and sex (BMI-for-age percentiles from the CDC or WHO). This calculator does not cover them.
- Pregnancy: BMI is not meaningful during pregnancy; use your pre-pregnancy weight when a midwife asks for it.
BMI Calculator FAQ
What is a healthy BMI?
For most adults a BMI from 18.5 to 24.9 is considered healthy. If you are of South Asian, East Asian or Southeast Asian descent, health risks begin to rise from about 23, so 18.5 to 22.9 is the healthier target.
How do I calculate BMI by hand?
Divide your weight in kilograms by your height in metres, then divide by your height again. With pounds and inches, multiply your weight by 703 and divide by your height in inches squared. The BMI calculator above shows this formula with your own numbers.
Is BMI different for men and women?
No. Adult BMI uses the same formula and the same categories for men and women. Women naturally carry more body fat at the same BMI, which is one reason a body fat estimate is a useful second check.
Why should Asians use lower BMI cut-offs?
At the same BMI, people of Asian descent tend to carry more body fat and face a higher risk of type 2 diabetes and heart disease than Europeans, so the WHO suggests action points of 23 (increased risk) and 27.5 (high risk).
Can I use this BMI calculator for my child?
No. Children and teenagers are still growing, so their BMI must be compared with BMI-for-age percentile charts. Ask your paediatrician or use your national growth charts.
I lift weights and my BMI says overweight. Is that wrong?
Possibly. Muscle is dense, so muscular people often score high without carrying excess fat. A waist measurement or body fat percentage tells you more.
How much should I weigh for my height?
The calculator shows the weight range that gives a healthy BMI for your exact height. For a single target figure from the classic formulas, try the ideal weight calculator, and use the calorie calculator to plan how to get there.