BMI Calculator
Calculate your Body Mass Index to see if you're at a healthy weight for your height.
What is BMI?
BMI stands for Body Mass Index. It's a simple measurement that uses your height and weight to calculate a number that indicates whether you're at a healthy weight, underweight, overweight, or obese.
BMI was developed in the 19th century by Belgian mathematician Adolphe Quetelet and has been used by doctors and health organizations worldwide as a quick screening tool for weight-related health risks.
While BMI is widely used, it's important to understand that it's just one of many factors in assessing overall health. It doesn't measure body fat directly or account for muscle mass, bone density, age, or sex differences.
How is BMI Calculated?
BMI is calculated using a simple formula:
Metric: BMI = weight (kg) / height (m)2
Imperial: BMI = (weight (lbs) / height (in)2) x 703
For example, a person who weighs 70 kg and is 1.75 m tall would have a BMI of 70 / (1.75 x 1.75) = 22.9, which falls in the "Normal weight" category.
BMI Categories Explained
The World Health Organization defines the following BMI categories for adults:
- Underweight (BMI below 18.5): May indicate malnutrition or other health conditions. Being underweight can weaken the immune system and increase risk of osteoporosis.
- Normal weight (BMI 18.5-24.9): Associated with the lowest risk of weight-related health problems. This is the target range for most healthy adults.
- Overweight (BMI 25-29.9): Indicates excess body weight that may increase risk of heart disease, type 2 diabetes, and other conditions.
- Obese (BMI 30 and above): Significantly increases risk of serious health conditions. Obesity is further divided into Class 1 (30-34.9), Class 2 (35-39.9), and Class 3 (40+).
Limitations of BMI
While BMI is a useful screening tool, it has several important limitations:
- Doesn't measure body fat: BMI can't distinguish between fat, muscle, bone, and water weight.
- Inaccurate for athletes: Muscular individuals may have a high BMI despite having low body fat.
- Age and sex differences: Older adults tend to have more body fat than younger adults at the same BMI. Women typically have more body fat than men at the same BMI.
- Ethnic variations: Health risks associated with BMI may vary between different ethnic groups.
Frequently Asked Questions
What is a healthy BMI?
A healthy BMI falls between 18.5 and 24.9. This range is associated with the lowest risk of weight-related health problems for most adults. However, BMI doesn't account for muscle mass, bone density, or fat distribution.
Is BMI accurate for athletes?
BMI may not be accurate for athletes or people with high muscle mass. Since muscle weighs more than fat, muscular individuals may have a high BMI while being at a healthy body fat percentage. Body fat percentage measurements are more accurate for athletes.
Should I use BMI or body fat percentage?
Both measurements have their place. BMI is a quick, free screening tool, while body fat percentage provides a more accurate picture of body composition. Ideally, use both along with other health markers like waist circumference and fitness level.
How can I lower my BMI?
To lower your BMI, focus on creating a moderate calorie deficit through a combination of healthy eating and regular exercise. Aim to lose 0.5-1 pound per week for sustainable results. Working with a personal trainer or nutritionist can help you create an effective plan.