Body Mass Index (BMI) is a quick way to estimate whether your weight is in a healthy range for your height. It’s widely used by doctors, nutritionists, and health organizations around the world.

Below is a clear, step‑by‑step guide on how to calculate BMI for adults, plus how to understand the result.

# 1. BMI Formula (Metric and Imperial)

# Metric formula (kilograms and meters)

Most health websites and tools use the metric formula:

[ \text{BMI} = \frac{\text{weight in kg}}{(\text{height in m})^2} ]

Steps:

Measure your weight in kilograms (kg).
Measure your height in meters (m).
Square your height: height × height.
Divide your weight by your squared height.

Example (Metric):

Weight: 70 kg
Height: 1.75 m

[ \text{BMI} = \frac{70}{1.75^2} = \frac{70}{3.0625} \approx 22.86 ]

Your BMI is about 22.9.

# Imperial formula (pounds and inches)

If you use pounds and inches, use:

[ \text{BMI} = \frac{\text{weight in lb} \times 703}{(\text{height in in})^2} ]

Steps:

Measure your weight in pounds (lb).
Measure your height in inches (in).
Square your height in inches.
Multiply your weight by 703.
Divide that result by your squared height.

Example (Imperial):

Weight: 154 lb
Height: 68 in (5 ft 8 in)

[ \text{BMI} = \frac{154 \times 703}{68^2} = \frac{108{,}262}{4{,}624} \approx 23.4 ]

Your BMI is about 23.4.

# 2. Quick BMI Calculation Steps (Cheat Sheet)

Metric (kg, cm):

Convert height from cm to m:
- height in m = height in cm ÷ 100
Apply: BMI = weight (kg) ÷ [height (m)]²

Imperial (lb, ft/in):

Convert height to total inches:
- total inches = (feet × 12) + remaining inches
Apply: BMI = [weight (lb) × 703] ÷ [height (in)]²

# 3. BMI Categories for Adults

Most major health organizations (such as the World Health Organization and CDC) use these standard BMI ranges for adults:

BMI (kg/m²)	Category
Less than 18.5	Underweight
18.5 – 24.9	Normal weight
25.0 – 29.9	Overweight
30.0 and above	Obesity

Using the earlier example:

BMI ≈ 22.9 → Normal weight
BMI ≈ 23.4 → Normal weight

# 4. Online BMI Calculators

If you don’t want to calculate manually, you can use trusted BMI calculators from reputable health sources:

Just enter your height and weight, and they’ll do the calculation and interpretation for you.

# 5. How Accurate Is BMI?

BMI is simple and useful for population-level screening, but it has limitations:

It does not distinguish between muscle and fat (a very muscular person can have a high BMI but low body fat).
It does not show fat distribution (belly fat vs fat in other areas).
It may be less accurate in:
- Athletes
- Elderly people
- Pregnant women
- People with very high or very low muscle mass

Because of this, BMI should be considered one tool among many. For a fuller picture of health, doctors may also look at:

Waist circumference
Blood pressure, cholesterol, blood sugar
Overall lifestyle, diet, and physical activity

For detailed guidance, see resources like:

# 6. What to Do After You Calculate Your BMI

If your BMI is in the normal range (18.5–24.9):
- Aim to maintain your weight with balanced nutrition and regular physical activity.
If your BMI is below 18.5 (underweight):
- Consider discussing with a healthcare provider or dietitian. You may need to increase calorie intake and review your diet.
If your BMI is 25 or above (overweight or obese):
- Talk with a healthcare professional about safe ways to reduce weight:
  - Adjusting diet
  - Increasing physical activity
  - Checking for other health conditions

You can read more practical guidelines at:

# 7. Summary: How to Calculate BMI

Use the correct formula:
- Metric: BMI = weight (kg) ÷ [height (m)]²
- Imperial: BMI = [weight (lb) × 703] ÷ [height (in)]²
Compare your result to standard adult BMI categories.
Use BMI as a guide, not a diagnosis—combine it with professional medical advice and other health checks.

If you share your height and weight, I can walk through the exact BMI calculation step by step.