Body Mass Index (BMI) Calculator

This free Body Mass Index (BMI) calculator for men and women is a tool to measure leanness or corpulence based on height and weight. It is widely used as a general indicator of whether a person has a healthy body weight. Learn how to calculate BMI and use our tool to determine your weight status, a useful signal for whether further testing is needed.

Your BMI is

23.0

Normal

152025303540

BMI Prime

0.92

Ponderal Index

12.9

Easy Calculation

Calculate your BMI using either Metric or US Customary units for height and weight.

Health Risk Insights

Understand the health risks associated with being underweight, overweight, or obese.

Related Indices

Calculates BMI Prime for easy comparison to the "normal" upper limit and Ponderal Index for very tall or short individuals.

Understanding BMI

The BMI calculation is designed to help determine an individual's weight status. The value obtained is used to classify a person into a specific category based on World Health Organization (WHO) recommendations for adults aged 20 or older. This BMI calculator for women and men uses the same standard categories. These categories are: underweight, normal weight, overweight, or obese.

How to Calculate BMI

The BMI formula varies depending on the unit system:

  • US Customary Units: BMI = 703 × (mass in lbs) / (height in inches)²
  • SI, Metric Units: BMI = (mass in kg) / (height in meters)²

For children and teens aged 2-20, the Centers for Disease Control and Prevention (CDC) uses percentile ranges rather than fixed BMI numbers to account for growth. A healthy weight for this group falls between the 5th and 85th percentiles on the CDC's growth charts.

Because being overweight or underweight can have significant health effects, BMI serves as a useful initial indicator of whether any additional testing or action is required. Generally, an adult should aim to maintain a BMI in the "Normal" range of 18.5 to 25 kg/m².

Health Risks Associated with BMI

Risks of Being Overweight (BMI ≥ 25)

According to the CDC, being overweight increases the risk of numerous serious health conditions, including:

  • High blood pressure
  • Coronary heart disease
  • Stroke
  • Type II diabetes
  • Higher levels of LDL cholesterol ('bad cholesterol')
  • Lower levels of HDL cholesterol (good cholesterol)
  • High levels of triglycerides
  • Gallbladder disease
  • Osteoarthritis
  • Sleep apnea and breathing problems
  • Certain cancers (endometrial, breast, colon, kidney, gallbladder, liver)
  • Low quality of life
  • Mental illnesses (clinical depression, anxiety)
  • Body pains and difficulty with physical functions
  • Increased risk of mortality

Risks of Being Underweight (BMI < 18.5)

Being underweight also carries significant health risks, which can include:

  • Increased risk of mortality
  • Malnutrition, vitamin deficiencies, and anemia
  • Decrease in immune function
  • Osteoporosis (a disease causing bone weakness)
  • Growth and development issues, especially in children and teenagers
  • Reproductive issues for women due to hormonal imbalances
  • Higher chance of miscarriage in the first trimester for women
  • Potential complications from surgery
  • Can be a sign of an underlying condition like anorexia nervosa

Limitations of BMI

BMI is an imperfect measure because it is an estimate of **excess body weight, not excess body fat**. It does not take body composition into account. Factors like age, sex, ethnicity, muscle mass, and activity level can influence its meaning.

  • Athletes and Bodybuilders: Highly muscular individuals may have a high BMI and be classified as overweight despite having a healthy body composition because muscle is heavier than fat.
  • Older Adults and Women: Older adults tend to have more body fat than younger adults with the same BMI. Similarly, women tend to have more body fat than men for an equivalent BMI. Our BMI calculator for women and men uses the same basic formula, so this should be kept in mind.
  • Children and Teens: For children, a high BMI could be due to increased levels of fat or fat-free mass (muscle, organs, etc.). It is a better indicator for obese children than for those who are merely overweight. Height and level of sexual maturation also influence their BMI and body fat.
  • BMI Prime: This is a ratio of a person's measured BMI to the normal upper limit (usually 25). The formula is BMI Prime = BMI / 25. It allows for a quick assessment of how a person's BMI compares to this limit and helps in comparing groups with different upper BMI limits. A person with a BMI prime less than 0.74 is classified as underweight; from 0.74 to 1 is normal; greater than 1 is overweight; and greater than 1.2 is obese.
  • Ponderal Index (PI): For very tall or short individuals, the Ponderal Index (which cubes height instead of squaring it) is considered more reliable, as BMI can record uncharacteristically high or low body fat levels at the extremes of the height spectrum.

While BMI is fairly indicative of body fat for 90-95% of the population, it should be considered alongside other measurements, not as the sole method for determining healthy body weight. For a more detailed look at your health, consider using our Calorie & Macro Calculator.