Calculate your Body Mass Index in seconds.
Our free BMI calculator helps you determine your Body Mass Index, a measure of body fat based on height and weight that applies to adult men and women. BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.
Using our BMI calculator is simple:
The BMI formula calculates body mass index using your weight and height:
For example, a person who weighs 70 kg and is 170 cm tall (1.7 meters) would have a BMI of 24.2:
BMI = 70 / (1.7 × 1.7) = 24.2
The World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) classify BMI ranges as follows:
| BMI | Weight Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk for some health problems |
| 18.5 - 24.9 | Normal weight | Lowest risk for health problems |
| 25.0 - 29.9 | Overweight | Increased risk for heart disease and diabetes |
| 30.0 - 34.9 | Obesity (Class 1) | High risk for health problems |
| 35.0 - 39.9 | Obesity (Class 2) | Very high risk for health problems |
| 40.0 and above | Obesity (Class 3) | Extremely high risk for health problems |
For more detailed information about BMI classifications, visit the CDC's BMI information page or the World Health Organization's obesity information.
While BMI is a useful screening tool, it has some limitations:
For a more comprehensive health assessment, consult with a healthcare provider who can evaluate other factors such as waist circumference, skinfold thickness measurements, diet, physical activity level, family history, and other health screenings. Learn more about BMI limitations and alternative measurements.
For children and teenagers, BMI is age and gender-specific and is often referred to as "BMI-for-age." In children, a high amount of body fat is different for boys and girls and changes with age. The CDC provides growth charts that show BMI as a percentile ranking, comparing a child's BMI to other children of the same age and gender.
For adults, BMI categories are the same for men and women of all ages. However, at the same BMI, women tend to have more body fat than men, and older adults tend to have more body fat than younger adults. The National Heart, Lung, and Blood Institute provides additional guidance on interpreting BMI for adults.
Being underweight may be associated with health issues such as:
If you're underweight, consider consulting with a healthcare professional to determine if there's an underlying medical cause. The NHS provides advice for gaining weight in a healthy way.
Maintaining a BMI in the normal range is associated with the lowest risk for weight-related health problems. The American Heart Association provides guidance on maintaining a healthy weight through balanced diet and regular physical activity.
Being overweight increases the risk for various health conditions, including:
However, some research suggests that being slightly overweight may not increase mortality in older adults. The Mayo Clinic offers advice on weight management strategies.
Obesity significantly increases the risk for serious health problems, including:
If your BMI indicates obesity, consider speaking with a healthcare provider about weight management options. The Obesity Action Coalition provides resources and support for individuals dealing with obesity.
The Harvard School of Public Health provides a helpful guide for creating balanced meals.
The World Health Organization provides physical activity recommendations for different age groups.
The National Institute of Diabetes and Digestive and Kidney Diseases offers guidance on behavioral strategies for weight management.
A BMI (Body Mass Index) calculator is a tool that uses your height and weight to calculate your BMI value, which is a numerical measure of your body fat level. BMI calculators help determine if you're at a healthy weight, underweight, overweight, or obese according to standard medical definitions.
BMI is a useful screening tool but has limitations. It doesn't directly measure body fat or distinguish between muscle and fat. Athletes or muscular individuals may have a high BMI but low body fat, while older adults might have a normal BMI but insufficient muscle mass. BMI should be one of several factors considered in a comprehensive health assessment, along with waist circumference, lifestyle factors, and other health indicators. For a complete health evaluation, consult a healthcare professional.
There's no strict guideline for how often to check your BMI. If you're actively working on weight management, checking every 1-3 months may be reasonable to track progress without becoming overly focused on small fluctuations. If your weight is stable and in a healthy range, an annual check during a regular medical check-up is typically sufficient. Remember that weight can fluctuate due to factors like water retention, so focus on long-term trends rather than day-to-day changes.
The standard BMI formula is the same for men and women. However, the interpretation can differ since women naturally tend to have higher body fat percentages than men at the same BMI. Some health professionals suggest that BMI thresholds might need to be sex-specific, but the standard categories are currently the same. For children and adolescents, BMI calculations are adjusted for age and sex using percentile rankings rather than fixed categories.
BMI estimates body fat indirectly based on height and weight, while body fat percentage measures the actual proportion of fat in your body. Body fat percentage is more accurate for assessing composition but requires specialized equipment like calipers, bioelectrical impedance scales, or more advanced methods like DEXA scans. BMI is widely used because it's simple, inexpensive, and correlates with health risks at a population level, though it may not be accurate for individuals with unusual body compositions.
The standard BMI categories were developed primarily based on data from European and North American populations. Research suggests that different ethnic groups may have different relationships between BMI, body fat, and health risks. For example, Asian populations tend to have higher body fat percentages at lower BMI values, leading some health organizations to recommend lower BMI thresholds for overweight and obesity classifications in Asian populations. The World Health Organization has recognized these differences and suggests potential adjustments for different ethnic groups.
Yes, it's possible to have a BMI in the "normal" range while still having health issues. This condition is sometimes called "normal weight obesity" or being "skinny fat," where a person has a normal BMI but a high body fat percentage and low muscle mass. Factors like diet quality, physical activity level, stress, sleep, and genetics all influence health independent of BMI. Conversely, some people with higher BMIs can be metabolically healthy with good cardiovascular fitness. BMI is just one measurement and should be considered alongside other health indicators.
Research suggests that the relationship between BMI and health outcomes may change with age. For older adults (generally over 65), some studies indicate that a slightly higher BMI (in the 25-29.9 range) may be associated with better health outcomes and lower mortality compared to a BMI in the lower end of the "normal" range. This phenomenon is sometimes called the "obesity paradox" in older adults. The reasons may include greater nutritional reserves during illness and protective effects against falls and fractures. However, individual health circumstances vary widely, so older adults should discuss weight management with their healthcare providers rather than focusing solely on BMI.