Health
BMI Calculator
Body mass index is a quick screen for whether your weight is in a healthy range for your height. Enter your measurements in metric or imperial units to see your BMI and its category.
Quick answer: BMI is weight (kg) ÷ height (m²): under 18.5 is underweight, 18.5–24.9 is normal, 25–29.9 is overweight, and 30+ is obese.
- Underweightbelow 18.5
- Normal18.5 – 24.9
- Overweight25 – 29.9
- Obese30 and above
- Healthy weight for your height129 – 174 lb
BMI is a screening tool, not a diagnosis. It doesn’t distinguish muscle from fat, so very muscular people may read high. Pair it with waist measurement and body-fat percentage for a fuller picture.
How it works
1. Gather height and weight
BMI uses just two inputs: your weight and your height. In metric it is weight in kilograms divided by height in meters squared; in U.S. units it is weight in pounds divided by height in inches squared, times 703. The calculator handles either unit system.
2. Compute weight over height squared
Squaring height scales the measure so it roughly normalizes across body sizes. The result is a single number that estimates whether your weight is proportionate to your height. It is a screening figure, not a direct measure of body fat.
3. Read the WHO category
The World Health Organization classifies BMI as underweight (below 18.5), normal (18.5 to 24.9), overweight (25 to 29.9), and obese (30 and above). These ranges flag potential health risk for further evaluation. Very muscular people may read high despite low body fat.
Frequently asked questions
How is BMI calculated?
BMI is weight in kilograms divided by height in meters squared (kg/m²). In imperial units it's 703 × weight in pounds ÷ height in inches squared.
What is a healthy BMI?
The WHO ranges are: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30+ obese. They're a screening guide, not a diagnosis.
What are the limits of BMI?
BMI doesn't distinguish muscle from fat, so very muscular people can read as 'overweight.' Use it alongside waist measurement and body-fat percentage for a fuller picture.
What is a healthy BMI range?
A BMI between 18.5 and 24.9 is classified as the normal or healthy range by the World Health Organization. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or higher is obese. These ranges are population screening categories, not a diagnosis for any individual.
Is BMI accurate for athletes and muscular people?
Not always — BMI cannot tell muscle from fat, so very muscular people can register as overweight or obese despite low body fat. For athletes and bodybuilders, measures like body-fat percentage or waist circumference give a clearer picture. BMI works best as a quick screen for the general population.
How do I calculate BMI by hand?
In U.S. units, divide your weight in pounds by your height in inches squared, then multiply by 703. For example, 160 pounds at 68 inches is 160 / (68 x 68) x 703, or about 24.3. In metric, divide kilograms by height in meters squared.
Does BMI differ for men and women?
The BMI formula and category ranges are the same for adult men and women. Women on average carry more body fat at the same BMI, so the number alone does not capture body composition differences. For children and teens, BMI is interpreted against age-and-sex percentile charts instead of fixed ranges.