What is BMI (Body Mass Index)?
Body Mass Index (BMI) is a widely used screening tool that estimates whether a person has a healthy body weight relative to their height. Developed in the 19th century by Adolphe Quetelet, it remains the most common initial health assessment used by doctors, dietitians, and fitness professionals worldwide.
BMI is calculated using a simple mathematical formula that divides your weight by the square of your height. The resulting number places you into one of four categories — Underweight, Normal, Overweight, or Obese — each with associated health risk guidance. While BMI is not a direct measure of body fat percentage, it is a reliable proxy for population-level health screening.
The BMI formula is straightforward and uses either metric or imperial values:
To calculate BMI in kg and feet, first convert your height from feet/inches to centimetres (1 foot = 30.48 cm), then apply the metric formula. Our calculator handles this conversion automatically — simply check the "kg and feet" option above.
How to Use This BMI Calculator
1
Select Your Unit System
Choose Metric (kilograms and centimetres) or Imperial (pounds and feet/inches). You can also enable the mixed mode to enter height in feet with weight in kg — a common preference for BMI calculator users in South Asia.
2
Choose Your Gender and Enter Your Age
Select male or female and enter your age. While the core BMI formula is identical for both genders, selecting your gender allows the calculator to display gender-specific healthy weight context alongside your result.
3
Enter Height and Weight
Input your height and body weight accurately. For best results use your height without shoes and your weight measured in the morning before eating.
4
Click "Calculate My BMI"
Your BMI score, category, healthy weight range, BMI Prime, and the amount of weight to lose or gain appear instantly. You can copy or share your result with a single tap.
BMI Calculator for Women
The standard BMI formula is the same for women as it is for men, but women typically carry a higher percentage of body fat at the same BMI value. A BMI of 22 in a woman may correspond to roughly 26–28% body fat, while the same BMI in a man may indicate 18–20% body fat. For a complete female body composition assessment, consider pairing your BMI result with a Body Fat Calculator or an Ideal Weight Calculator.
Checking BMI for Males
To check BMI for males, the same WHO classification applies: under 18.5 is underweight, 18.5–24.9 is healthy, 25–29.9 is overweight, and 30+ is obese. However, men tend to carry more muscle mass, which weighs more than fat. A muscular male athlete may register as "overweight" or even "obese" purely due to lean muscle mass — which is why BMI should always be interpreted alongside waist circumference and other health markers.
Limitations of BMI
BMI is a population-level screening tool, not a clinical diagnostic. It does not distinguish between muscle mass and fat mass, nor does it account for age-related changes in body composition, ethnic differences in body fat distribution, or differences between the sexes. It is best used as a starting point alongside other metrics such as waist-to-hip ratio, body fat percentage, blood pressure, and metabolic markers.