How can body mass index (BMI) be determined by calculation or using a nomogram?

SouravNovember 8, 2024

Answer

Body Mass Index (BMI) can be determined through calculation or by using a nomogram. Here’s how both methods work:

Calculation of BMI

Formula

BMI is calculated using the following formulas, depending on the measurement system used:

1. Metric System:
   BMI=weight kg/height m^2 ​
2. Imperial System:
   BMI=weight lb/height in^2 ×703

Steps for Calculation

1. Measure Height and Weight:
   • Weight should be measured in kilograms (kg) or pounds (lb).
   • Height should be measured in meters (m) or inches (in).
2. Perform the Calculation:
   • For example, if a person weighs 75 kg and is 1.77 m tall:
     BMI=75/(1.77)^2=75/3.13≈23.96
   • For a person weighing 160 lb and standing 5 feet 8 inches tall (68 inches):
     BMI=160/(68)^2×703=160/4624×703≈24.3

Using a Nomogram

What is a Nomogram?

A nomogram is a graphical representation that allows users to estimate BMI based on height and weight without performing calculations manually.

How to Use a BMI Nomogram

1. Locate Height: Find the individual’s height on one axis of the nomogram.
2. Locate Weight: Find the corresponding weight on another axis.
3. Draw a Line: Draw a straight line connecting the height and weight points.
4. Read BMI: The point where the line intersects the BMI scale indicates the individual’s BMI.

Example of Interpretation

• A nomogram typically displays BMI categories, such as underweight, normal weight, overweight, and obesity, allowing users to quickly assess their weight status based on their BMI value.

Summary of BMI Categories

The following categories are commonly used to classify BMI values:

• Underweight: BMI < 18.5
• Normal Weight: BMI 18.5 – 24.9
• Overweight: BMI 25 – 29.9
• Obesity Class I: BMI 30 – 34.9
• Obesity Class II: BMI 35 – 39.9
• Obesity Class III: BMI ≥ 40