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What is the body mass index (BMI)?
Body mass index (BMI) is a person's weight in kilograms divided by the square of height in meters. It indicates the amount of body fat. BMI is the most inexpensive screening tool to measure body fat. Although it does not directly measure body fat, it can be correlated with a more direct measure of body fat. The various categories of BMI include: BMI values less than 18.5 are considered underweight BMI values between 18.5 and 24.9 are healthy BMI values between 25 and 30 are overweight BMI values greater than 40 are considered obese Maintaining a healthy weight offers the following health benefits: How to calculate BMI: A guide to understanding your body mass index Understanding the relationship between your weight and height is a crucial step in managing your health. This is where BMI becomes relevant. In this article, we will explain how to calculate your BMI, how to interpret the results using a BMI chart, and how to use tools like a BMI calculator or an ideal weight calculator to help you better understand your goals for health.
What is the formula to calculate BMI? Body mass index (BMI) is a measurement of body fat that is calculated based on height and weight. How to calculate BMIThe BMI equation is simple: BMI = weight (kg)/height (m)2 For those using pounds and inches: BMI = weight (lb) × 703/height (in)2 While it's useful to know how to calculate BMI manually, many prefer using a digital BMI calculator for quick and accurate results. The formula for calculating BMI is given in Table 1, or you can use the body mass index calculator below. Table 1. The Formula for Calculating BMI Measurement Units Formula and CalculationKilograms and meters (or centimeters) Formula: weight (kg) / height (m)2 The formula for BMI is weight in kilograms divided by height in meters squared. If height has been measured in centimeters, divide by 100 to convert this to meters. Pounds and inches Formula: 703 x weight (lbs) / height (in)2 When using English measurements, pounds should be divided by inches squared. This should then be multiplied by 703 to convert from lbs/inches2 to kg/m2.Example of BMI calculation If a person weighs 65 kg and their height is 165 cm (1.65 m), the BMI is calculated as 65 ÷ (1.65)2 = 23.87 kg/m2, which means that the person has a BMI of 23.87 kg/m2 and is considered to have a healthy weight. When calculating in pounds and inches, if a person weighs 120 lbs and their height is 5 feet 6 inches (66 inches), the BMI is calculated as 703 x 120/(66)2 = 19.3 kg/m2, which means that the person has a BMI of 19.3 kg/m2 and is considered to have a healthy weight. How do you calculate your BMI? BMI CalculatorTo use this calculator: The default BMI of 16.6 shown on the tool is for a 5'5" person who weighs 100 lbs. Use the switch on top to pick either metric or imperial measurements. Set the height and weight dials to match your own height and weight. View your BMI number at the center of the tool and see where you fall on the obesity chart. BMI values are based on clinical data about averages for these measurements across a wide swath of people. The body mass index (BMI) is used to assess your weight relative to your height. This BMI calculator allows you to easily screen yourself for obesity or extra, unhealthy weight. If your results from the calculator aren't in the healthy range, don't worry too much. People with muscular builds may be classified as obese, even with a low body fat percentage and optimum health, simply because the BMI formula uses only two data points.
What is the ideal BMI? Once you calculate the BMI, it is important to interpret the values using a BMI table or body mass index chart. These tools differentiate BMI into categories that signify potential health risks. BMI ranges according to the World Health Organization (WHO) are as follows: Table 2. World Health Organization BMI Ranges BMI Range CategoryBelow 18.5 Underweight 18.5-24.9 Normal weight 25.0-29.9 Overweight 30.0 and above Obese An ideal BMI calculation depends on your height and gender. See the ideal BMI chart below to determine which category you may fall under. Table 3. Ideal Weight in lbs According to Height Height Minimal risk(BMI under 25 kg/m2) Moderate risk High risk 4'10'' 118 or less 119–142 143 or more 4'11'' 123 or less 124–147 148 or more 5'0'' 127 or less 128–152 153 or more 5'1'' 131 or less 132–157 158 or more 5'2'' 135 or less 136–163 164 or more 5'3'' 140 or less 141–168 169 or more 5'4'' 144 or less 145–173 174 or more 5'5'' 149 or less 150–179 180 or more 5'6'' 154 or less 155–185 186 or more 5'7'' 158 or less 159–190 191 or more 5'8'' 163 or less 164–196 197 or more 5'9'' 168 or less 169–202 203 or more 5'10'' 173 or less 174–208 209 or more 5'11'' 178 or less 179–214 215 or more 6'0'' 183 or less 184–220 221 or more 6'1'' 188 or less 189–226 227 or more 6'2'' 193 or less 194–232 233 or more 6'3'' 199 or less 200–239 240 or more 6'4'' 204 or less 205–245 246 or more Health News
Frequently asked questions (FAQs) about how to calculate BMI Is BMI accurate?While BMI is the most popular tool for assessing weight status, it is not always accurate and has limitations, as it does not distinguish between muscle and body fat. You may need additional tools. What is BMI used for?BMI is a screening tool that estimates body fat based on a person's height and weight. It is commonly used to assess whether an individual has a healthy weight for their height. BMI helps classify people into weight status categories (underweight, normal weight, overweight, or obese), which can indicate potential health risks related to body weight. What are the limitations of BMI?BMI doesn't differentiate between muscle mass and body fat, and it ignores fat distribution. It may lead to misclassification by overestimating the body fat in muscular individuals (such as athletes) and underestimating elderly individuals with low muscle mass. Healthcare providers use additional tools along with BMI to assess a person's health status and risks. What is the normal BMI for females?A normal BMI for females, as well as for males, typically falls within the range of 18.5 to 24.9. Although adult females generally have a higher percentage of body fat compared to males, the same BMI chart is used for both sexes to assess weight status. What is the correct BMI for my age?For adults aged 18 and older, the correct BMI generally falls within the 18.5 to 24.9 range. However, for children and teenagers, BMI is interpreted differently — it's based on age- and sex-specific growth charts. Always use the appropriate BMI calculator for your age to ensure accurate results. What are alternatives to BMI?Some alternatives to BMI include waist circumference, waist-to-hip ratio, waist-to-height ratio, body roundness index (BRI), and various body composition assessments, such as DEXA scans and skinfold measurements.
Medically Reviewed on 7/28/2025 References
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