1. What is BMI?

Body Mass Index (BMI) is a simple index of weight-for-height that is commonly used to classify underweight, normal weight, overweight and obesity in adults. It is calculated by dividing weight in kilograms by the square of height in meters.

2. How Does the Calculator Work?

The calculator uses the standard BMI formula:

Where:

• \( weight \) — Body weight in kilograms
• \( height \) — Height in meters

Explanation: The formula provides a simple numeric measure of a person's thickness or thinness, allowing health professionals to discuss weight problems objectively with their patients.

3. Importance of BMI Calculation

Details: BMI provides the most useful population-level measure of overweight and obesity as it is the same for both sexes and for all ages of adults. However, it should be considered a rough guide because it may not correspond to the same degree of fatness in different individuals.

4. Using the Calculator

Tips: Enter weight in kilograms and height in meters. For height, you can convert from cm to m by dividing by 100 (e.g., 175 cm = 1.75 m). All values must be valid (weight > 0, height > 0).

5. Frequently Asked Questions (FAQ)

Q1: What are the BMI categories for adults?
A: Underweight (<18.5), Normal weight (18.5-24.9), Overweight (25-29.9), Obese (≥30).

Q2: Is BMI accurate for everyone?
A: BMI may not be accurate for athletes (muscle weighs more than fat), pregnant women, the elderly, or those with unusual body compositions.

Q3: How often should I check my BMI?
A: For most adults, checking every 6-12 months is sufficient unless you're actively trying to change your weight.

Q4: What's a healthy BMI range for New Zealanders?
A: The healthy range is 18.5-24.9 for most adults, though some ethnic groups (like Māori and Pacific peoples) may have different health risks at the same BMI.

Q5: Should children use this calculator?
A: No, children and teens need age- and sex-specific BMI charts as their body composition changes with growth.