1. What is BMI?

Body Mass Index (BMI) is a simple calculation using a person's height and weight. The formula is BMI = kg/m² where kg is a person's weight in kilograms and m² is their height in meters squared. It's widely used in the UK as a screening tool for weight categories.

2. How BMI is Calculated

The calculator uses the standard BMI formula:

Where:

• Weight — Measured in kilograms (kg)
• Height — Measured in meters (m)

Example: For a person weighing 70kg and 1.75m tall: 70 ÷ (1.75 × 1.75) = 22.9 kg/m²

3. BMI Categories

UK NHS Categories:

• Below 18.5 — Underweight
• 18.5 - 24.9 — Healthy weight
• 25 - 29.9 — Overweight
• 30 and above — Obese

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: Is BMI accurate for everyone?
A: BMI has limitations - it may overestimate body fat in athletes and underestimate it in older people with less muscle mass.

Q2: What's a healthy BMI range?
A: For most adults, 18.5 to 24.9 is considered healthy. However, individual circumstances may vary.

Q3: Should children use this calculator?
A: No, children and teens need age- and sex-specific BMI calculations as their bodies change with growth.

Q4: What if I know my weight in stones?
A: Convert stones to kg by multiplying by 6.35 (1 stone = 6.35kg).

Q5: What if I know my height in feet/inches?
A: Convert feet to meters (1 foot = 0.3048m) and inches to meters (1 inch = 0.0254m).