BMI Calculator
The Body Mass Index (BMI) Calculator can be used to calculate BMI value and corresponding weight status while taking age into consideration. Use the "Metric Units" tab for the International System of Units or the "Other Units" tab to convert units into either US or metric units. Note that the calculator also computes the Ponderal Index in addition to BMI, both of which are discussed below in detail.
BMI is a measurement of a person's leanness or corpulence based on their height and weight, and is intended to quantify tissue mass. It is widely used as a general indicator of whether a person has a healthy body weight for their height. Specifically, the value obtained from the calculation of BMI is used to categorize whether a person is underweight, normal weight, overweight, or obese depending on what range the value falls between. These ranges of BMI vary based on factors such as region and age, and are sometimes further divided into subcategories such as severely underweight or very severely obese. Being overweight or underweight can have significant health effects, so while BMI is an imperfect measure of healthy body weight, it is a useful indicator of whether any additional testing or action is required. Refer to the table below to see the different categories based on BMI that are used by the calculator.
The BMI Calculator calculates Body Mass Index (BMI) value and corresponding weight status while taking age into consideration. It computes BMI using height and weight, and also calculates the Ponderal Index and BMI Prime. The formula is: BMI = mass(kg) / height²(m) or BMI = 703 × mass(lbs) / height²(in).
Maintaining a healthy BMI is important for overall health and well-being. A BMI within the normal range (18.5-25) is associated with lower risk of weight-related health problems, while values outside this range may indicate the need for lifestyle changes or medical consultation. This calculator provides a quick and easy way to assess your body weight status and understand potential health risks associated with your current BMI category.
This is the World Health Organization's (WHO) recommended body weight based on BMI values for adults. It is used for both men and women, age 20 or 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 |
Healthy Weight Ranges by Height
Knowing the healthy weight range for your height provides a practical target. Using the normal BMI range of 18.5-25 kg/m², the following table shows approximate healthy weight ranges for adults:
| Height (metric) | Healthy weight range (kg) | Height (US) | Healthy weight range (lbs) |
|---|---|---|---|
| 150 cm | 42 - 56 kg | 4'11" | 92 - 124 lbs |
| 155 cm | 44 - 60 kg | 5'1" | 98 - 132 lbs |
| 160 cm | 47 - 64 kg | 5'3" | 104 - 141 lbs |
| 165 cm | 50 - 68 kg | 5'5" | 111 - 150 lbs |
| 170 cm | 54 - 72 kg | 5'7" | 118 - 160 lbs |
| 175 cm | 57 - 77 kg | 5'9" | 125 - 169 lbs |
| 180 cm | 60 - 81 kg | 5'11" | 133 - 179 lbs |
| 185 cm | 63 - 86 kg | 6'1" | 140 - 190 lbs |
| 190 cm | 67 - 90 kg | 6'3" | 148 - 200 lbs |
These ranges are based on WHO guidelines for adults aged 20 and older. Individual healthy weights may vary depending on muscle mass, bone density, and body composition. Use this table as a reference alongside your BMI calculation.
The Centers for Disease Control and Prevention (CDC) recommends BMI categorization for children and teens between age 2 and 20.
| Category | Percentile Range |
|---|---|
| Underweight | < 5% |
| Healthy weight | 5% - 85% |
| At risk of overweight | 85% - 95% |
| Overweight | > 95% |
Being overweight increases the risk of a number of serious diseases and health conditions. Below is a list of said risks, according to the Centers for Disease Control and Prevention (CDC):
- High blood pressure
- Higher levels of LDL cholesterol, which is widely considered "bad cholesterol," lower levels of HDL cholesterol, considered to be good cholesterol in moderation, and high levels of triglycerides
- Type II diabetes
- Coronary heart disease
- Stroke
- Gallbladder disease
- Osteoarthritis, a type of joint disease caused by breakdown of joint cartilage
- Sleep apnea and breathing problems
- Certain cancers (endometrial, breast, colon, kidney, gallbladder, liver)
- Low quality of life
- Mental illnesses such as clinical depression, anxiety, and others
- Body pains and difficulty with certain physical functions
- Generally, an increased risk of mortality compared to those with a healthy BMI
Generally, a person should try to maintain a BMI below 25 kg/m², but ideally should consult their doctor to determine whether or not they need to make any changes to their lifestyle in order to be healthier.
Being underweight has its own associated risks, listed below:
- Malnutrition, vitamin deficiencies, anemia (lowered ability to carry blood vessels)
- Osteoporosis, a disease that causes bone weakness, increasing the risk of breaking a bone
- A decrease in immune function
- Growth and development issues, particularly in children and teenagers
- Possible reproductive issues for women due to hormonal imbalances that can disrupt the menstrual cycle. Underweight women also have a higher chance of miscarriage in the first trimester
- Potential complications as a result of surgery
- Generally, an increased risk of mortality compared to those with a healthy BMI
In some cases, being underweight can be a sign of some underlying condition or disease such as anorexia nervosa, which has its own risks. Consult your doctor if you think you or someone you know is underweight, particularly if the reason for being underweight does not seem obvious.
The Body Mass Index (BMI) is calculated by dividing a person's weight by their height squared. Two formula variants exist depending on the measurement system used.
BMI Formula (Metric)
Where: weight_kg = body mass in kilograms (kg), height_m = height in meters (m)
Example: A person weighing 72.57 kg with a height of 1.78 m: BMI = 72.57 / 1.78² = 22.9
BMI Formula (US Customary)
Where: weight_lbs = body weight in pounds (lbs), height_in = height in inches (in), 703 = conversion factor
Example: A person weighing 160 lbs with a height of 70 inches: BMI = 703 × 160 / 70² = 22.9
BMI Prime
A simplified ratio where BMI ≥ 25 is considered "overweight" threshold.
Ponderal Index
Alternative to BMI that uses cubed height instead of squared, more reliable for extreme heights.
Although BMI is a widely used and useful indicator of healthy body weight, it does have its limitations. BMI is only an estimate that cannot take body composition into account. Due to a wide variety of body types as well as 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 a person's healthy body weight. In thin children, the difference in BMI can also be due to fat-free mass.
In adults:
BMI cannot be fully accurate because it is a measure of excess body weight, rather than excess body fat. BMI is further influenced by factors such as age, sex, ethnicity, muscle mass, body fat, and activity level, among others. For example, an older person who is considered a healthy weight, but is completely inactive in their daily life may have significant amounts of excess body fat even though they are not heavy. This would be considered unhealthy, while a younger person with higher muscle composition of the same BMI would be considered healthy. In athletes, particularly bodybuilders who would be considered overweight due to muscle being heavier than fat, it is entirely possible that they are actually at a healthy weight for their body composition. According to the CDC:
- Older adults tend to have more body fat than younger adults with the same BMI.
- Women tend to have more body fat than men for an equivalent BMI.
- Muscular individuals and highly trained athletes may have higher BMIs due to large muscle mass.
In children and adolescents:
The same factors that limit the efficacy of BMI for adults can also apply to children and adolescents. Additionally, height and level of sexual maturation can influence BMI and body fat among children. BMI is a better indicator of excess body fat for obese children than it is for overweight children, whose BMI could be a result of increased levels of either fat or fat-free mass (all body components except for fat, which includes water, organs, muscle, etc.). In thin children, the difference in BMI can also be due to fat-free mass.
That being said, BMI is fairly indicative of body fat for 90-95% of the population, and can effectively be used along with other measures to help determine an individual's healthy body weight.
Ethnic and racial considerations:
The relationship between BMI and body fat percentage varies across ethnic groups. The World Health Organization recognizes that individuals of Asian descent tend to have higher body fat at lower BMI values, increasing cardiovascular and metabolic risk at BMI levels considered normal for other populations. For this reason, some Asian countries have adopted lower thresholds: overweight at BMI ≥23 and obesity at BMI ≥27.5.
Conversely, individuals of Black African or Caribbean descent tend to have lower body fat and higher lean muscle mass at equivalent BMI values compared to Caucasian populations. Pacific Islander populations generally have higher lean body mass, which can result in higher BMI without corresponding increases in body fat. These differences underscore the importance of considering ethnicity alongside BMI and suggest that complementary measurements may provide a more complete health picture.
For more information, see the Body Fat Calculator.
While BMI is a useful screening tool at the population level, several alternative measurements provide additional insight into individual body composition and health risk:
Waist-to-Height Ratio (WHtR)
The waist-to-height ratio is calculated by dividing waist circumference by height. A WHtR below 0.5 is considered healthy for most adults. This measurement accounts for central adiposity, which is a stronger predictor of cardiovascular risk than BMI alone. WHtR is simple to measure with a tape measure and requires only basic division, making it accessible for regular self-assessment.
Waist Circumference
Waist circumference directly measures abdominal fat and is a strong predictor of visceral fat and associated health risks. According to the CDC and the National Institutes of Health, a waist circumference above 35 inches (88 cm) for women and 40 inches (102 cm) for men indicates increased risk for metabolic syndrome, type 2 diabetes, and cardiovascular disease. This measurement is particularly useful for individuals within a normal BMI range who carry excess abdominal fat.
Body Fat Percentage
Body fat percentage directly measures the proportion of fat mass relative to total body weight, distinguishing between fat and lean mass. Common methods include skinfold calipers, bioelectrical impedance analysis (BIA), dual-energy X-ray absorptiometry (DEXA), and hydrostatic weighing. Skinfold calipers offer a practical balance of accuracy and cost, while DEXA provides the highest accuracy at a higher cost. Unlike BMI, body fat percentage can identify normal-weight obesity, where an individual has a healthy BMI but excessive body fat.
Achieving and maintaining a healthy BMI involves sustainable lifestyle habits rather than extreme measures:
- Balanced nutrition: Focus on whole foods including vegetables, fruits, lean proteins, whole grains, and healthy fats. Limit processed foods, added sugars, and trans fats. The CDC recommends filling half your plate with fruits and vegetables at each meal for a nutrient-rich diet.
- Regular physical activity: Aim for at least 150 minutes of moderate-intensity aerobic activity or 75 minutes of vigorous-intensity activity per week, combined with muscle-strengthening activities on two or more days per week, following CDC and WHO guidelines.
- Adequate sleep: Poor sleep quality and short sleep duration are associated with weight gain and higher BMI. Adults should aim for 7-9 hours of quality sleep per night to support metabolic health and appetite regulation.
- Stress management: Chronic stress can promote abdominal fat storage through hormonal changes involving cortisol. Incorporate stress-reduction techniques such as meditation, deep breathing, or regular physical activity.
- Regular monitoring: Track your weight and BMI periodically to identify trends. Even modest weight loss of 5-10% of body weight can significantly improve health outcomes for individuals who are overweight or obese.
- Consult healthcare providers: Work with a doctor or registered dietitian to develop a personalized plan that accounts for your medical history, lifestyle, and health goals. Self-directed weight programs may not be appropriate for everyone.
See the Calorie Calculator, BMR Calculator, and TDEE Calculator for tools to help plan your nutrition and activity goals.
- Is BMI accurate for athletes?
- BMI does not distinguish between muscle and fat mass. Athletes with high muscle mass may be classified as overweight despite low body fat. Body fat percentage is more appropriate for these individuals.
- Can BMI be used for children?
- Yes, but BMI-for-age percentiles are used instead of adult categories. The CDC provides growth charts accounting for age and sex differences during development.
- What are BMI limitations for older adults?
- Older adults often lose muscle mass and bone density, lowering BMI even with excess body fat. BMI may underestimate health risks in the elderly.
- Does BMI apply equally across ethnic groups?
- Research suggests health risks at given BMI levels vary by ethnicity. People of Asian descent may have higher risks at lower BMI thresholds.
- What is a healthy BMI for older adults?
- Some research suggests that a slightly higher BMI range of 24-27 may be protective for adults over 65 by providing nutritional reserves during illness. Individual health status and functional capacity should guide the target range rather than a fixed number.
- How accurate is BMI for children during puberty?
- BMI during puberty can be misleading due to growth spurts, changing body composition, and differences in maturation timing. Pediatricians use BMI-for-age percentiles from CDC growth charts rather than fixed adult thresholds, plotted on sex-specific charts.
- What is the difference between BMI and body fat percentage?
- BMI is a simple ratio of weight to height and does not distinguish between fat and muscle. Body fat percentage directly measures the proportion of fat tissue. Two individuals with identical BMI can have very different body fat percentages depending on muscle mass.
- Can BMI be used during pregnancy?
- BMI is not appropriate for assessing weight status during pregnancy due to the weight of the fetus, amniotic fluid, and increased blood volume. Healthcare providers use separate gestational weight gain guidelines based on pre-pregnancy BMI.
- How often should I check my BMI?
- Monitoring BMI every 1-3 months is reasonable for most adults tracking weight changes. More frequent measurements may show normal daily fluctuations in weight due to hydration, food intake, and other factors.
- What is the healthy BMI range for Asian populations?
- Many Asian health organizations use lower BMI thresholds: overweight at 23-27.5 kg/m² and obese at over 27.5 kg/m², reflecting higher metabolic risk at lower BMI levels in these populations.
- Is BMI a good measure for bodybuilders?
- BMI is not suitable for bodybuilders or strength athletes. High muscle mass can push BMI into the overweight or obese range despite very low body fat. Body fat percentage or waist-to-height ratio are better alternatives.
Last updated: June 5, 2026
The notAcalculator Editorial Team
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