1. What is BMI?

Body Mass Index (BMI) is a measure of body fat based on height and weight that applies to adult men and women. It provides a simple numeric measure of a person's thickness or thinness.

2. How Does the Calculator Work?

The calculator uses the UK stone formula:

Where:

• \( weight \) — Weight in stones (1 stone = 14 pounds)
• \( height_{feet} \) — Height in feet
• \( height_{inches} \) — Remaining height in inches
• 703 — Conversion factor (kg/m² to lb/in²)

3. BMI Categories

Standard BMI Categories:

• Underweight: BMI less than 18.5
• Normal weight: BMI 18.5 to 24.9
• Overweight: BMI 25 to 29.9
• Obese: BMI 30 or greater

4. Using the Calculator

Tips: Enter weight in stones (e.g., 11.5 for 11 stone 7 pounds), height in feet and inches. All values must be valid (weight > 0, height > 0).

5. Frequently Asked Questions (FAQ)

Q1: Why use stone measurements?
A: This calculator is designed for the UK where stone is commonly used for body weight (1 stone = 14 pounds).

Q2: Is BMI accurate for athletes?
A: BMI may overestimate body fat in muscular individuals and underestimate it in older people with less muscle mass.

Q3: What are the limitations of BMI?
A: BMI doesn't account for muscle mass, bone density, overall body composition, or racial/ethnic differences.

Q4: Should children use this calculator?
A: No, children and teens need age- and sex-specific BMI percentiles.

Q5: What's a healthy BMI range?
A: For most adults, 18.5 to 24.9 is considered healthy, but consult your doctor for personalized advice.