How to use the BMI Calculator
- Choose Metric (kilograms and centimetres) or Imperial (pounds, feet and inches).
- Enter your weight and height.
- Press Calculate to see your BMI, the WHO category, and the weight range that corresponds to a BMI of 18.5 to 24.9 at your height.
BMI formula
In imperial units the calculator first converts pounds to kilograms (× 0.45359) and inches to metres (× 0.0254).
WHO adult BMI categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obese |
Worked example
A person who weighs 70 kg and is 175 cm (1.75 m) tall: BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9, which is in the normal range.
Healthy weight range for common heights
These are the weights that give a BMI between 18.5 and 24.9, the WHO normal range for adults:
| Height | Weight for BMI 18.5 to 24.9 |
|---|---|
| 150 cm | 41.6 to 56.0 kg |
| 155 cm | 44.4 to 59.8 kg |
| 160 cm | 47.4 to 63.7 kg |
| 165 cm | 50.4 to 67.8 kg |
| 170 cm | 53.5 to 72.0 kg |
| 175 cm | 56.7 to 76.3 kg |
| 180 cm | 59.9 to 80.7 kg |
What BMI does not tell you
- Muscle versus fat. Athletes and people with a lot of muscle can have a high BMI without carrying extra body fat.
- Where fat is stored. Fat around the waist carries different health risks from fat elsewhere, and BMI cannot show this.
- Age and body type. Older adults often have more body fat at the same BMI, and body shape varies between people and populations.
- Your overall health. Blood pressure, blood sugar, cholesterol, fitness and family history all matter.
How to use your result
Treat BMI as a starting point for a conversation with a doctor, not as a verdict. If your result is outside the normal range, a doctor or dietitian can tell you whether it matters in your case and what a sensible plan looks like.
Frequently asked questions
What is BMI?
Body Mass Index is a number that compares your weight to your height. It is a quick screening tool used to group adults into weight categories.
Is BMI accurate for everyone?
No. BMI does not separate muscle from fat, so very muscular people can show as overweight. It also does not show where fat is stored. Use it as a starting point and talk to a doctor for a proper assessment.
Does this calculator work for children?
No. For children and teenagers BMI is interpreted using age- and sex-specific percentile charts. Ask a paediatrician or use the growth charts from a health authority.
Why do some Indian guidelines use different BMI cut-offs?
Several guidelines for Asian populations use lower cut-offs because health risks such as type 2 diabetes can rise at a lower BMI. A BMI of 23 or above is often treated as overweight and 25 or above as obese. Your doctor can tell you which to follow.
How can I move towards a healthy weight?
Aim for gradual change: balanced meals, regular activity, enough sleep and steady habits. For personal advice, especially if you have a medical condition or are pregnant, consult a doctor or dietitian.
Is BMI the same for men and women?
The standard adult BMI formula and categories are the same for men and women. Body fat levels differ between sexes at the same BMI, which is one reason BMI is only a screening number.
How often should I check my BMI?
BMI changes slowly, so checking every few months is plenty. If you are working on your weight, tracking waist size and how you feel alongside BMI gives a fuller picture.