BMI Calculator
Calculate your body mass index (BMI) from your height and weight, in metric or US units, and see the adult weight category and the range of weights that corresponds to a healthy BMI for your height. It is a screening tool, not a diagnosis.
Result
Enter your height and weight to see your BMI.
The calculation runs in this browser tab. Nothing you enter is uploaded, saved or logged.
What is the body mass index?
BMI is your weight in kilograms divided by the square of your height in metres. It is a quick, cheap way to judge whether weight is in proportion to height, used by health organisations to screen for weight categories in adults. A person 1.70 m tall weighing 68 kg has a BMI of 68 ÷ 1.70² = 23.5.
For adults the World Health Organization categories are: under 18.5 underweight; 18.5 to 24.9 healthy weight; 25 to 29.9 overweight; 30 and over obesity, divided into class 1 (30 to 34.9), class 2 (35 to 39.9) and class 3 (40 and over). BMI does not measure body fat directly, so it can misclassify very muscular people, older adults and people with different body compositions.
How to use the BMI Calculator
- Choose metric (centimetres and kilograms) or US units (feet, inches and pounds).
- Enter your height and your weight.
- Read your BMI, your category and the healthy weight range for your height, with how far you are from it.
- Use Copy result to copy the BMI and category. Remember that BMI is only one of many health indicators.
Formula
- Metric
- BMI = weight (kg) ÷ height (m)²
- US units
- BMI = 703 × weight (lb) ÷ height (in)²
- Weight for a given BMI
- weight = BMI × height (m)²
The factor 703 in the US formula is the exact conversion between the two unit systems, 0.45359237 ÷ 0.0254², rounded. The calculator uses the exact values.
The healthy range uses the BMI limits 18.5 and 24.9. It is the weight at those BMI values for your height.
Worked example
An adult 170 cm tall who weighs 68 kg. These are the results the calculator gives:
| Question | Result |
|---|---|
| Input: Units | Metric (centimetres, kilograms) |
| Input: Height | 170 cm |
| Input: Weight | 68 kg |
| Your BMI | 23.5 |
| Category (adults) | Healthy weight |
| BMI to two decimals | 23.53 |
| Healthy weight for your height | 53.5 kg to 72.0 kg (117.9 lb to 158.6 lb) |
| Compared with the healthy range | You are within the healthy range for your height. |
| Your measurements | 170.0 cm, 68.0 kg |
Assumptions and limits
- BMI is for adults aged 20 and over. For children and teenagers, health authorities compare BMI with growth charts for age and sex, which this calculator does not do.
- It is not suitable during pregnancy, and it can mislead for athletes and very muscular people (too high), older adults who have lost muscle (too low), and people of short stature.
- Some health bodies use lower thresholds for people of Asian descent, because health risks can appear at a lower BMI. The categories shown are the general WHO adult categories.
- The category is based on the exact BMI. A value such as 24.96 is displayed as 25.0 but is still in the healthy category; the two-decimal BMI is listed in the details.
- This is not medical advice. Talk to a doctor about your weight and health.
Frequently asked questions
How do I calculate my BMI?
Divide your weight in kilograms by your height in metres squared. For 68 kg and 1.70 m that is 68 ÷ 2.89 = 23.5. In US units, multiply the weight in pounds by 703 and divide by the height in inches squared.
What is a healthy BMI?
For adults, 18.5 to 24.9 is the healthy weight range, according to the World Health Organization. Below 18.5 is underweight and 25 or above is overweight.
What weight is healthy for my height?
The weight that gives a BMI between 18.5 and 24.9. At 170 cm that is 53.5 to 72.0 kg. The calculator shows this range for your own height, in kilograms and pounds.
Is BMI accurate for athletes?
Not always. Muscle weighs more than fat, so a muscular athlete can have a high BMI without carrying excess fat. In that case waist measurement or body-fat measurements are more informative.
Does BMI work for children?
Not with these categories. For people under 20, BMI is compared with growth charts for their age and sex, usually by a doctor or nurse.
Does BMI tell me about my health?
Only partly. It is a screening number linked to health risks across populations, but it says nothing about fitness, diet, blood pressure, or where fat is stored. Use it as a starting point for a conversation with a health professional.