What Is BMI?

Body Mass Index (BMI) is a numerical value calculated from a person's height and weight. It provides a simple, inexpensive, and widely used screening tool to categorize individuals into weight status categories — underweight, normal weight, overweight, and obese. BMI was developed by Belgian mathematician Adolphe Quetelet in the 1830s and has been used as a population health screening tool by the World Health Organization and public health agencies worldwide for decades.

How BMI Is Calculated

BMI is calculated by dividing a person's weight in kilograms by the square of their height in meters. In metric units: BMI = weight (kg) / height (m)². In imperial units, the formula is: BMI = (weight in pounds × 703) / height in inches². For example, a person who is 5 feet 10 inches tall (70 inches) and weighs 170 pounds has a BMI of (170 × 703) / (70²) = 119,510 / 4,900 = 24.4.

BMI Categories for Adults

The standard BMI categories for adults aged 18 and over are as follows. A BMI below 18.5 is classified as underweight. A BMI between 18.5 and 24.9 is classified as normal or healthy weight. A BMI between 25.0 and 29.9 is classified as overweight. A BMI of 30.0 or above is classified as obese, with further subcategories of Class 1 obesity (30-34.9), Class 2 obesity (35-39.9), and Class 3 or severe obesity (40 and above).

What BMI Does Not Tell You

BMI is a useful screening tool but has significant limitations that are important to understand. BMI does not distinguish between muscle and fat. A highly muscular athlete may have a BMI in the overweight range despite having very low body fat. Conversely, someone with a normal BMI may have high body fat and low muscle mass — a condition sometimes called "normal weight obesity." BMI also does not account for age-related changes in body composition, where older adults tend to have more fat and less muscle than younger adults at the same BMI.

BMI does not account for where fat is distributed on the body. Abdominal fat (fat around the waist) is significantly more associated with cardiovascular disease and metabolic disorders than fat stored in the hips and thighs. Two people with identical BMIs can have very different health risk profiles depending on their fat distribution. For this reason, waist circumference is often used alongside BMI as a complementary health indicator.

Healthy Weight Ranges by Height

A healthy BMI of 18.5 to 24.9 corresponds to different weight ranges depending on height. For someone 5 feet 4 inches tall, the healthy weight range is approximately 108 to 145 pounds. For someone 5 feet 10 inches tall, the healthy range is approximately 129 to 174 pounds. For someone 6 feet tall, the healthy range is approximately 140 to 188 pounds. Our BMI calculator shows your specific healthy weight range based on your height.

How to Use Our Free BMI Calculator

Our free BMI calculator at cookiescursor.com supports both Imperial (pounds and inches) and Metric (kilograms and centimeters) units. Enter your height and weight, and the calculator instantly shows your BMI, your weight category with color coding, and your healthy weight range for your height. This tool is for informational purposes only — consult a healthcare professional for medical advice about your weight and health.

Frequently Asked Questions

Is BMI accurate for everyone?
BMI is a useful population-level screening tool but is less accurate for individuals, particularly athletes, elderly people, and those with unusual body compositions. Use it as one data point among several health indicators.

What is a healthy BMI for women vs men?
The same BMI categories apply to both men and women. However, women naturally have higher body fat percentages than men at the same BMI, so some health researchers advocate for slightly different BMI thresholds by gender.

Does BMI apply to children?
For children and teenagers, age and sex-specific BMI percentiles are used instead of adult categories. Our calculator is designed for adults aged 18 and over.

What should I do if my BMI is in the overweight range?
Consult your doctor. BMI alone does not determine health risk — your doctor will consider additional factors including blood pressure, blood glucose, cholesterol, family history, and lifestyle factors.

Can I have a normal BMI and still be unhealthy?
Yes. Normal weight obesity — having a normal BMI but high body fat — is possible. Conversely, some people with overweight BMIs have excellent metabolic health markers.

How often should I check my BMI?
BMI is most useful for tracking trends over time. Checking every few months is reasonable for most adults. Daily tracking is unnecessary as normal weight fluctuations can obscure meaningful trends.

Calculate Your BMI Now

Use our free BMI calculator for instant results in Imperial or Metric units. For informational purposes only — consult a healthcare professional for medical advice. No signup required.