What Is BMI?
Body Mass Index (BMI) is a numerical value calculated from a person's weight and height. It was developed by Belgian mathematician Adolphe Quetelet in the 19th century and later became a widely used screening measure for population-level weight status.
BMI is not a diagnostic tool — it does not directly measure body fat or diagnose any medical condition. Instead, it classifies individuals into weight categories that are associated with varying levels of health risk. Doctors use it as a first step to identify people who may need further assessment, alongside other metrics like blood pressure, cholesterol, blood glucose, and waist circumference.
How BMI Is Calculated
The BMI formula is straightforward: divide your weight in kilograms by your height in meters squared.
BMI = Weight (kg) / Height² (m²)
Weight
Your body weight in kilograms (or converted from pounds: lbs ÷ 2.205)
Height²
Your height in meters squared. Convert cm to meters first: divide by 100. Then square it. e.g. 175 cm = 1.75 m → 1.75² = 3.0625
Example: A person weighing 70 kg with a height of 175 cm has a BMI of 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9—within the standard Healthy Weight range.
How to Interpret an Adult BMI Result
Standard adult BMI categories do not change by age or sex. However, two adults with the same BMI can have different body composition and health profiles. Muscle mass, fat distribution, medical history, fitness, medicines, laboratory findings, and other factors can change how useful the number is for an individual.
Treat the result as a starting point for context, not a diagnosis or a grade. If the result is unexpected, your weight has changed without explanation, or you have health concerns, a qualified healthcare professional can assess it alongside more relevant information.
BMI Limitations
BMI is a useful population-level screening tool, but it has several well-documented limitations that are important to understand when interpreting your result:
⚠ Doesn't distinguish fat from muscle
A highly muscular person may have a high BMI because BMI counts total body mass. It cannot separate lean mass from adipose tissue.
⚠ Doesn't show fat distribution
BMI does not indicate where body fat is stored. Abdominal fat distribution can add information that height and weight alone do not provide.
⚠ Risk can vary across populations
The relationship between BMI and metabolic risk is not identical for every population. Some healthcare guidelines use additional action points or clinical context for particular ethnic groups rather than relying on the standard categories alone.
⚠ Not an adult-category tool for people under 20
For ages 2 through 19, BMI must be interpreted using age- and sex-specific BMI-for-age percentiles and growth charts.
⚠ Doesn't reflect fitness level
BMI does not measure cardiovascular fitness, strength, activity level, blood pressure, cholesterol, glucose, or other indicators used in a broader assessment.
BMI and Health Risks
Across large populations, higher BMI categories are associated with a greater likelihood of several health conditions. An individual's actual risk can be higher or lower depending on medical history, fat distribution, fitness, age, and other factors:
Overweight (25–29.9)
- ·Elevated blood pressure
- ·Higher LDL cholesterol
- ·Increased risk of type 2 diabetes
- ·Sleep apnea
- ·Joint stress (osteoarthritis)
Obesity category (30+)
- ·Cardiovascular disease
- ·Type 2 diabetes
- ·Certain cancers
- ·Stroke
- ·Fatty liver disease
- ·Sleep apnea
What to Do With Your BMI Result
Look Beyond One Number
- BMI does not distinguish muscle from body fat
- It does not show where body fat is distributed
- Medical history and laboratory findings can change the interpretation
Check the Context
- Confirm that height and weight were entered accurately
- Consider whether a recent weight change was intentional
- Use the same conditions when tracking changes over time
Ask for Individual Advice
- Discuss unexpected or concerning results with a healthcare professional
- Children and teens need BMI-for-age assessment
- Pregnancy, high muscularity, and some health conditions need added context
Real-World BMI Examples
| Height | Weight | BMI | Category |
|---|---|---|---|
| 160 cm (5'3") | 45 kg (99 lbs) | 17.6 | Underweight |
| 165 cm (5'5") | 60 kg (132 lbs) | 22.0 | Healthy Weight |
| 175 cm (5'9") | 80 kg (176 lbs) | 26.1 | Overweight |
| 180 cm (5'11") | 100 kg (220 lbs) | 30.9 | Class 1 Obesity |
| 170 cm (5'7") | 55 kg (121 lbs) | 19.0 | Healthy Weight |
| 185 cm (6'1") | 95 kg (209 lbs) | 27.8 | Overweight |
Health Information Sources
The adult category ranges and age guidance on this page follow current public-health information from the U.S. Centers for Disease Control and Prevention. The interpretation notes also reflect National Institutes of Health guidance that BMI is a screening tool and does not diagnose body fatness.
Frequently Asked Questions
Medical Disclaimer: This BMI calculator is for informational and educational purposes only. BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age, sex, ethnicity, or overall health. Please consult a qualified healthcare professional before making any health or medical decisions based on your BMI result.