What is BMI?
BMI (Body Mass Index) is your weight in kilograms divided by the square of your height in meters. It is a quick, widely used way to gauge whether your weight is in a healthy range for your height.
Formula: BMI = weight (kg) ÷ (height (m) × height (m))
WHO categories
- Underweight — < 18.5
- Normal — 18.5 – 24.9
- Overweight — 25 – 29.9
- Obese — ≥ 30
Good to know
BMI can be less accurate for very muscular people, pregnant women, and children. Use it as a general guide and consult a healthcare professional for a full assessment.
How do I calculate BMI?
To calculate BMI (body mass index), divide your weight in kilograms by your height in meters squared. Example: a person weighing 65 kg who is 170 cm (1.70 m) tall has a BMI of 65 ÷ (1.70 × 1.70) = 22.49, which falls in the normal range.
Steps to calculate BMI
- Convert height from centimeters to meters by dividing by 100 (170 cm becomes 1.70 m).
- Square the height in meters (1.70 × 1.70 = 2.89).
- Divide weight in kilograms by that squared height (65 ÷ 2.89).
- Round the result to one or two decimal places to get your BMI (22.49).
- Compare the BMI value against the category ranges to see where it falls.
BMI formula
BMI = weight (kg) ÷ height (m)^2
- weight = body weight in kilograms (pounds divided by 2.205)
- height = body height in meters (centimeters divided by 100)
Quick BMI answers
What is the BMI of someone who is 170 cm tall and weighs 70 kg?
BMI is 24.2 (70 ÷ (1.70 × 1.70)), in the normal weight range.
What is the BMI of someone who is 160 cm tall and weighs 50 kg?
BMI is 19.5 (50 ÷ (1.60 × 1.60)), also in the normal range.
What is the BMI of someone who is 180 cm tall and weighs 80 kg?
BMI is 24.7 (80 ÷ (1.80 × 1.80)), normal range, just below the 25 overweight cutoff.
Is a BMI of 25 considered overweight?
Yes. WHO classifies 25.0 to 29.9 as overweight; 25.0 is the lower edge of that range, and 24.9 or below is still normal weight.
What BMI counts as underweight?
Below 18.5 is classified as underweight under the WHO standard this calculator uses.
What BMI counts as obese?
30 or above is classified as obese; 25 to 29.9 is overweight, and 18.5 to 24.9 is normal weight.
What is the BMI of someone 190 cm tall weighing 90 kg?
BMI is 24.9 (90 ÷ (1.90 × 1.90)), right at the top edge of the normal range.
What is the BMI of someone 175 cm tall weighing 100 kg?
BMI is 32.7 (100 ÷ (1.75 × 1.75)), in the obese range.
Example BMI by height and weight
| Height | Weight | BMI | Category |
|---|
| 170 cm | 65 kg | 22.49 | Normal |
| 160 cm | 50 kg | 19.53 | Normal |
| 180 cm | 90 kg | 27.78 | Overweight |
| 155 cm | 45 kg | 18.73 | Normal |
| 175 cm | 100 kg | 32.65 | Obese |
Frequently asked questions
What are the BMI category ranges?
Under 18.5 is underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight, and 30 or above is obese. These World Health Organization ranges apply to most adults but are only a screening guide.
When is BMI not accurate?
BMI does not distinguish muscle from fat, so muscular athletes can show a high BMI while carrying low body fat. It is also less reliable for children, pregnant women, and adults over 65, since body composition differs from the general adult population it was calibrated on.
Is BMI the same for men and women?
The formula and category thresholds are the same for men and women in this calculator. Some clinical guidance adjusts interpretation by sex and ethnicity, but the standard BMI ranges shown here do not vary by gender.
What is a healthy weight range for my height?
Multiply 18.5 and 24.9 by your height in meters squared to get the lower and upper bounds. For 170 cm (1.70 m), that range is 18.5 × 2.89 = 53.5 kg to 24.9 × 2.89 = 72.0 kg.
BMI is a simple screening tool based on height and weight only; it does not measure body fat percentage, muscle mass, or fat distribution directly. Use the result as a general reference and consult a doctor or dietitian for a full health assessment.