BMI Calculator
Enter your height and weight to calculate your Body Mass Index (BMI) and see which category it falls into.
How BMI is worked out
BMI is your weight in kilograms divided by your height in metres, squared. In pounds and inches the formula is 703 × weight ÷ height². For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which sits in the healthy range.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity, class I |
| 35.0 – 39.9 | Obesity, class II |
| 40.0 and above | Obesity, class III |
What BMI can and cannot tell you
BMI is a quick screening number, not a diagnosis. It cannot tell muscle from fat, so very muscular people can score as overweight, and older adults who have lost muscle can score as healthy while carrying too much fat. It also says nothing about where fat is stored. Waist measurement, blood pressure, blood sugar and cholesterol often tell you more about your health than BMI alone.
Different populations carry health risk at different BMI levels. The World Health Organization has noted that many Asian populations face higher risk of type 2 diabetes and heart disease at lower BMI values, and suggests extra caution from about 23. Adult categories also do not apply to children and teenagers, whose BMI is compared with age- and sex-specific growth charts instead.
If your result is outside the healthy range, or you are worried about your weight, a GP or practice nurse can look at the whole picture. For related numbers try the body fat calculator, the ideal weight calculator and the calorie calculator.
FAQ
What is BMI?
Body Mass Index (BMI) is a simple calculation using height and weight — weight in kilograms divided by height in metres squared — used as a general screening measure for weight categories.
What do the BMI categories mean?
Under 18.5 is considered underweight, 18.5–24.9 is considered a typical range, 25–29.9 is considered overweight, and 30 and above is considered obese, according to World Health Organization classifications.
Is BMI accurate for everyone?
BMI doesn't distinguish between muscle and fat, so it can be misleading for very muscular people, athletes, older adults, or during pregnancy. It's a general population screening tool, not a diagnostic measurement for any individual.
Should I make health decisions based on BMI alone?
BMI is one data point among many. Body composition, waist circumference, activity level, and overall health all matter — a doctor or healthcare provider can give a fuller picture than BMI alone.
What is a healthy BMI for my height?
For adults, a BMI from 18.5 to 24.9 is the typical range. For someone 170 cm tall that is roughly 53 to 72 kg. The table above shows other heights.
Is BMI the same for men and women?
The adult categories are the same for men and women. Body fat differs between the sexes at the same BMI, which is one reason BMI is a rough guide.
Can I use BMI for children?
No. Children and teenagers are measured against growth charts for their age and sex. Ask a doctor or nurse if you have concerns about a child's weight.
About this tool
This calculator works out Body Mass Index from height and weight in either metric or imperial units, and shows which standard category the result falls into. It's a general screening tool, not medical advice — everything runs instantly in your browser with nothing stored.
Worked examples
The calculator uses weight in kilograms divided by height in metres squared. In imperial units it uses 703 × weight in pounds ÷ height in inches squared. The default entries, 170 cm and 70 kg, give a BMI of 24.2.
| Height | Weight | BMI | Category in this calculator |
|---|---|---|---|
| 170 cm | 70 kg | 24.2 | Typical range |
| 160 cm | 80 kg | 31.2 | Obese |
| 180 cm | 95 kg | 29.3 | Overweight |
| 155 cm | 45 kg | 18.7 | Typical range |
| 175 cm | 75 kg | 24.5 | Typical range |
| Height | Weight | BMI | Category in this calculator |
|---|---|---|---|
| 5 ft 7 in | 154 lb | 24.1 | Typical range |
| 5 ft 10 in | 200 lb | 28.7 | Overweight |
| 6 ft 0 in | 165 lb | 22.4 | Typical range |
The category shown by the calculator follows the standard adult cut-offs: under 18.5, 18.5 to 24.9, 25 to 29.9, and 30 or above.
What weight range does that mean for my height?
Rearranging the formula gives the weights that fall in the typical BMI range of 18.5 to 24.9:
| Height | Metric weight range | Imperial weight range |
|---|---|---|
| 150 cm (4 ft 11 in) | 42 to 56 kg | 92 to 124 lb |
| 160 cm (5 ft 3 in) | 47 to 64 kg | 104 to 141 lb |
| 170 cm (5 ft 7 in) | 53 to 72 kg | 118 to 159 lb |
| 180 cm (5 ft 11 in) | 60 to 81 kg | 132 to 178 lb |
| 190 cm (6 ft 3 in) | 67 to 90 kg | 147 to 198 lb |
These ranges are wide because people of the same height can have very different builds.
What BMI can and cannot tell you
- It is a screening number, not a diagnosis. It compares weight with height and does not measure body fat directly.
- Muscle counts as weight. A very muscular person can have a high BMI with a low body fat percentage.
- Body shape and fat distribution matter. Waist circumference adds information that BMI misses.
- Cut-offs vary by population. Health organisations suggest lower action thresholds for some Asian populations, and BMI can be less reliable for older adults and people who are very short or tall.
- Children and teenagers are assessed with age- and sex-specific growth charts, not these adult categories.
This tool is for general information and is not medical advice. If you are concerned about your weight, speak to a doctor or other healthcare professional.