Understand Your BMI
Use our calculator to determine your Body Mass Index.
BMI CALCULATOR
Enter your information into the provided fields to determine your macros.
What Is BMI?
Body Mass Index (BMI) is a measurement of a person’s leanness or corpulence based on their height and weight. It is widely used as a general indicator of whether a person has a healthy body weight for their height. The value obtained from BMI calculation is used to categorize whether a person is underweight, normal weight, overweight, or obese.
While BMI is an imperfect measure — it cannot distinguish between muscle and fat — it is a useful screening tool that indicates whether additional testing or lifestyle changes may be needed. It is used by the WHO, CDC, and medical professionals worldwide.
BMI Table for Adults (WHO)
The World Health Organization’s recommended body weight classification based on BMI, for adults age 20 and older:
| Classification | BMI Range (kg/m2) |
|---|---|
| Severe Thinness | < 16 |
| Moderate Thinness | 16 – 17 |
| Mild Thinness | 17 – 18.5 |
| Normal | 18.5 – 25 |
| Overweight | 25 – 30 |
| Obese Class I | 30 – 35 |
| Obese Class II | 35 – 40 |
| Obese Class III | > 40 |
BMI Chart for Adults
This graph shows BMI categories based on World Health Organization data. The colors represent major BMI categories for different height-weight combinations.
BMI for Children & Teens (Ages 2-20)
The CDC recommends BMI categorization for children and teens using age- and sex-specific percentiles, because body composition varies greatly as children grow:
| Category | Percentile Range |
|---|---|
| Underweight | < 5th percentile |
| Healthy Weight | 5th – 85th percentile |
| At Risk of Overweight | 85th – 95th percentile |
| Overweight | > 95th percentile |
Boys: Ages 2-20
View CDC Growth Chart (PDF)Girls: Ages 2-20
View CDC Growth Chart (PDF)Risks of Being Overweight
- High blood pressure
- Higher LDL (“bad”) cholesterol
- Type II diabetes
- Coronary heart disease
- Stroke
- Gallbladder disease
- Osteoarthritis
- Sleep apnea
- Certain cancers
- Clinical depression and anxiety
Risks of Being Underweight
- Malnutrition and vitamin deficiencies
- Osteoporosis (bone weakness)
- Decreased immune function
- Growth and development issues
- Reproductive issues in women
- Surgical complications
- Anemia
- Increased mortality risk
Limitations of BMI
BMI is only an estimate that cannot take body composition into account. Due to the wide variety of body types, distribution of muscle, bone mass, and fat, BMI should be considered along with other measurements rather than being used as the sole method for determining healthy body weight.
Key limitations include: older adults tend to have more body fat than younger adults at the same BMI; women tend to have more body fat than men at equivalent BMI; and muscular athletes may register as “overweight” despite having healthy body fat levels. That said, BMI is fairly indicative for 90-95% of the population.
BMI Formula
US Customary Units
BMI = 703 x weight (lbs) / height2 (in)
Example: 703 x 160 / 702 = 23.0
Metric Units
BMI = weight (kg) / height2 (m)
Example: 72.57 / 1.7782 = 23.0
BMI Prime & Ponderal Index
BMI Prime is the ratio of your BMI to the upper limit of “normal” BMI (25 kg/m2). A value less than 0.74 indicates underweight, 0.74-1.0 is normal, and above 1.0 is overweight. It provides a quick way to see how far your BMI is from the healthy threshold.
Ponderal Index (PI) is similar to BMI but cubes the height instead of squaring it, making it more reliable for very tall or short individuals. PI = height (in) / cube root of weight (lbs).
Frequently Asked Questions
How is BMI calculated?
BMI is calculated by dividing your weight by the square of your height. In metric units: BMI = kg / m2. In US units: BMI = 703 x lbs / inches2. This calculator handles all unit conversions automatically — just enter your height and weight in whichever system you prefer.
Is BMI accurate for athletes?
BMI has known limitations for athletes and highly muscular individuals. Muscle is denser than fat, so a person with significant muscle mass may register as “overweight” by BMI despite having low body fat. For athletes, body fat percentage measurements (via calipers, DEXA scan, or bioelectrical impedance) provide a more accurate picture of body composition.
What is a healthy BMI?
According to the World Health Organization, a healthy BMI for adults falls between 18.5 and 25 kg/m2. However, optimal BMI can vary by age, sex, and ethnicity. Generally, maintaining a BMI below 25 while staying above 18.5 is associated with the lowest health risks.
Does BMI apply differently to children?
Yes. For children and teens (ages 2-20), BMI is interpreted using age- and sex-specific percentile charts from the CDC, because body fat changes dramatically during growth. A child’s BMI is compared to other children of the same age and sex, rather than using fixed thresholds like adults.
What is BMI Prime and Ponderal Index?
BMI Prime is your BMI divided by 25 (the upper normal limit). A value of 1.0 means you’re exactly at the threshold. Below 1.0 is normal, above 1.0 is overweight. It’s useful for quickly seeing how far you are from the healthy range.
Ponderal Index uses the cube of height instead of the square, making it more accurate for very tall or very short people where standard BMI can be misleading.
Should I use BMI alone to assess my health?
No. BMI is a screening tool, not a diagnosis. It should be used alongside other measurements like waist circumference, body fat percentage, blood pressure, cholesterol, and blood sugar levels. A comprehensive health assessment from a qualified professional gives the most accurate picture. That said, BMI is effective for 90-95% of the population as an initial indicator.