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BMI calculator
Enter a height and weight to see the body mass index for an adult, where it sits on the WHO scale, and the healthy weight range for that height.
Height · Weight
Everything is calculated on your device. Your entries are saved in this browser only, so they are here when you come back.
BMI
Enter a height and weight to see the BMI.
- Underweight< 18.5
- Healthy weight18.5 – 24.9
- Overweight25.0 – 29.9
- Obesity class I30.0 – 34.9
- Obesity class II35.0 – 39.9
- Obesity class III≥ 40.0
BMI is a screening measure, not a diagnosis. It doesn’t see muscle, bone or where weight is carried. For children and teenagers, BMI is read against growth charts for age and sex, so these adult categories don’t apply. A doctor or nurse can explain what your numbers mean for you.
How BMI is calculated
Body mass index is weight divided by height squared: BMI = kg ÷ m². In imperial units the same number comes from 703 × lb ÷ in².
Worked example: a person 170 cm tall who weighs 65 kg has a BMI of 65 ÷ (1.70 × 1.70) = 65 ÷ 2.89 ≈ 22.5. In imperial units, 5 ft 7 in (67 in) and 150 lb give 703 × 150 ÷ (67 × 67) ≈ 23.5.
The healthy weight range shown for a height is simply the weight that gives a BMI from 18.5 to 24.9. For 170 cm that is about 53.5 kg to 72 kg.
The WHO categories for adults
- Below 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25 to 29.9: overweight
- 30 to 34.9: obesity class I
- 35 to 39.9: obesity class II
- 40 and above: obesity class III
These cut-offs are for adults aged 20 and over. Some health services use lower thresholds for people of Asian descent, because health risks can start at a lower BMI.
What BMI can and can’t tell you
BMI is quick and needs only two numbers, which is why it is widely used for screening. It is a starting point for a conversation, not a judgement about a person.
- It doesn’t separate muscle from fat, so athletes can read as overweight while being very fit.
- It doesn’t show where weight is carried. Waist size adds useful information.
- It isn’t used the same way in pregnancy, and it can read differently for older adults.
- For children and teenagers, BMI is compared with growth charts for their age and sex (percentiles), not with the adult categories.
If you have questions about your weight or health, a doctor, nurse or dietitian can look at the full picture.
FAQ
What is a healthy BMI for adults?
The World Health Organization uses 18.5 to 24.9 as the healthy weight range for adults. Below 18.5 is underweight and 25 or more is overweight.
How do I calculate BMI by hand?
Divide your weight in kilograms by your height in metres squared. For example, 65 kg at 1.70 m is 65 ÷ 2.89 ≈ 22.5. With pounds and inches, multiply the weight by 703 and divide by the height in inches squared.
Is BMI accurate?
It is a useful screening number for groups of people, but it doesn’t measure body fat directly or show where fat is stored. Muscular people, older adults and pregnant women may get a misleading result.
Can I use this BMI calculator for children?
Not for the categories. For children and teenagers, BMI is compared with growth charts for their age and sex. A paediatrician or school nurse can do that properly.
What weight is healthy for my height?
Enter your height and the calculator shows the weight range that gives a BMI from 18.5 to 24.9. It is a guide only; body build and health matter too.
Are my height and weight stored anywhere?
Only in this browser, so the calculator remembers them next time. Nothing is sent to a server.
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