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How can body mass index (BMI) be determined by calculation or using a nomogram?
How can body mass index (BMI) be determined by calculation or using a nomogram?
Answered step-by-step
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:
- Metric System:
BMI=weight kg/height m^2
- Imperial System:
BMI=weight lb/height in^2 ×703
Steps for Calculation
- Measure Height and Weight:
- Weight should be measured in kilograms (kg) or pounds (lb).
- Height should be measured in meters (m) or inches (in).
- 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
- For example, if a person weighs 75 kg and is 1.77 m tall:
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
- Locate Height: Find the individual’s height on one axis of the nomogram.
- Locate Weight: Find the corresponding weight on another axis.
- Draw a Line: Draw a straight line connecting the height and weight points.
- 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
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