Body Mass Index - BMI Calculator Explained

By Last updated: February 28, 2023

BMI – Body Mass Index Calculator

Body Mass Index (BMI) measures a person's weight relative to height. A high BMI may indicate high body fat, leading to health issues. However, it's important to note that BMI is not a comprehensive diagnostic tool for determining body fatness or overall health.[1]

It's primarily used as a screening tool to identify weight categories associated with health risks. Using your weight and height, BMI calculators can determine if you are underweight, normal, overweight, or obese, giving you a starting point for your weight management goals.

Body Mass Index Formula

To calculate a person's BMI, you need to:

  1. Write down the weight in kilograms (kg).
  2. Divide it by the square of the height in meters (m).

Here is the formula for metric units: BMI = weight (kg) / height2 (m2)

$${BMI} = \frac{weight\ (kg)}{height^2\ (m^2)}$$

For imperial units: BMI = weight (lb) / height2 (in2) x 703

$${BMI} = \frac{weight\ (lb)}{height^2\ (in^2)} \times 703$$

Example 1: BMI Calculation

What is the body mass index (BMI) of a 35-year-old person weighing 165 lbs and 5 feet 7 inches tall?

To calculate the BMI, we can use the following formula:

${BMI} = \frac{weight\ (lb)}{height^2\ (in^2)} \times 703$
${BMI} = \frac{165\ (lb)}{(5'7")^2\ (in^2)} \times 703$
${BMI} = \frac{165)}{(60" + 7")^2} \times 703$
${BMI} = \frac{165}{(67")^2} \times 703$
${BMI} = \frac{165}{4,479} \times 703$
${BMI} = {0.0367565159278236} \times 703$
${BMI} = 25.84$

So, the described person has a BMI of 25.84.

You can save time and still get the same result using our BMI calculator as an alternative option. Just input your basic information, such as height and weight, into the designated fields, and you'll have your BMI value within seconds.

BMI Calculation Example
BMI Calculation Example

Body Mass Index Chart

According to the CDC[2] and the WHO[3], the BMI of adults who are over 20 years old falls into the following categories:

Weight StatusBMI
Underweight< 18.5
Normal weight
18.5 - 24.9
25.0 - 29.9
Obesity Class I30.0 - 34.9
Obesity Class II35 - 39.9
Obesity Class III≥ 40
Table 1: Body mass index classification

Example 2: Identifying Weight Status

What is a person's weight status with a BMI score 25.84?

Referring to the body mass index classification, the BMI score 25.84 falls into the 25.0 to 29.9 range, identified as a pre-obesity or overweight status.

Factors that may influence the accuracy of BMI measurement

BMI is a practical tool to assess weight status, but it's essential to understand the factors that can impact its accuracy. Age, gender, ethnicity, and genetic variations can affect BMI readings, leading to variations in body composition. As a result, the interpretation of BMI values may be impacted.

It is important to note that BMI may not be the best indicator for specific groups, including children[4], pregnant women[5], and older adults. These groups require alternative assessments to evaluate weight status accurately.

It is essential to understand that BMI (Body Mass Index) alone cannot determine overall health. Cardiovascular fitness, blood pressure, blood glucose, and cholesterol levels are essential to overall health. Therefore, you should consider BMI measurements alongside these other factors for a comprehensive evaluation when assessing weight status and overall health.

Understanding these limitations and considering individual circumstances will help ensure a more accurate evaluation of weight status and overall health.


What is BMI?

BMI is an acronym for Body Mass Index, which measures body fat based on an individual's height and weight.

Is BMI the same for men and women?

Yes, BMI is calculated similarly for men and women[2]. However, the healthy BMI range can vary slightly depending on age and ethnicity.

Is BMI the most accurate measure of body composition?

While BMI is commonly used to measure body composition, it has some limitations. BMI doesn't differentiate between muscle mass and fat mass, which can result in inaccuracies for people with more muscle mass. This limitation is especially relevant for athletes, bodybuilders, and people who regularly engage in strength training exercises.

Alternative methods like body fat percentage measurements or waist circumference can provide a more precise assessment of body composition for such individuals. These methods consider muscle mass and fat distribution, resulting in a more comprehensive overall health and fitness analysis.

Despite its limitations, BMI is still a valuable tool for evaluating weight-related health risks in the general population. It provides an accessible and straightforward way to keep track of weight status and serves as a starting point for weight management goals.

We strive to make our calculator apps as accurate as possible, but they cannot replace a professional doctor. Our website provides information for informational purposes, and it's not medical advice. Please consult your healthcare provider before making any decisions based on the results provided by our tool.
BMI – Body Mass Index Calculator

BMI – Body Mass Index Calculator App

About this app

Use our free BMI calculator web app to calculate your body mass index by simply entering your height and weight.

App availability

You can use the calculator for free as a PWA web app online or install it locally on any modern operating system, including Android, iOS, Windows 11/10, and macOS.

BMI - Body Mass Index Calculator QR
Scan Me
Use BMI - Body Mass Index Calculator as Web App
Related Calculators


5 Sources

  1. ⬆️ CDC. Body Mass Index (BMI). Centers for Disease Control and Prevention. Published June 3, 2022. Accessed January 12, 2024.
  2. ⬆️ ⬆️ CDC. About Adult BMI. Centers for Disease Control and Prevention. Published June 3, 2022. Accessed January 13, 2024.
  3. ⬆️ World. A healthy lifestyle - WHO recommendations. Published May 6, 2010. Accessed January 12, 2024.
  4. ⬆️ CDC. About Child & Teen BMI. Centers for Disease Control and Prevention. Published September 24, 2022. Accessed January 13, 2024.
  5. ⬆️ NHS Choices. What is the body mass index (BMI)? Published 2024. Accessed January 13, 2024.