How to Calculate BMI: The Complete Guide
Body Mass Index (BMI) is a widely used measure to assess whether a person has a healthy body weight for their height. While it's not a perfect measure, it's a useful starting point for understanding your weight status.
What is BMI?
BMI is a simple calculation using your height and weight. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is still used by healthcare providers worldwide as a screening tool.
The BMI Formula
Metric Formula
BMI = Weight (kg) ÷ Height² (m²)
Imperial Formula
BMI = (Weight (lbs) × 703) ÷ Height² (inches²)
Step-by-Step Calculation
Metric Example:
Weight: 70 kg | Height: 1.75 m
Step 1: Square the height: 1.75 × 1.75 = 3.0625
Step 2: Divide weight by height²: 70 ÷ 3.0625 = 22.9
Weight: 70 kg | Height: 1.75 m
Step 1: Square the height: 1.75 × 1.75 = 3.0625
Step 2: Divide weight by height²: 70 ÷ 3.0625 = 22.9
Imperial Example:
Weight: 154 lbs | Height: 5'9" (69 inches)
Step 1: Square the height: 69 × 69 = 4,761
Step 2: Multiply weight by 703: 154 × 703 = 108,262
Step 3: Divide: 108,262 ÷ 4,761 = 22.7
Weight: 154 lbs | Height: 5'9" (69 inches)
Step 1: Square the height: 69 × 69 = 4,761
Step 2: Multiply weight by 703: 154 × 703 = 108,262
Step 3: Divide: 108,262 ÷ 4,761 = 22.7
BMI Categories
Under 18.5
Underweight
Underweight
18.5 - 24.9
Normal Weight
Normal Weight
25 - 29.9
Overweight
Overweight
30+
Obese
Obese
BMI Chart
| Height | Normal (18.5-24.9) | Overweight (25-29.9) |
|---|---|---|
| 5'0" (152 cm) | 97-127 lbs | 128-152 lbs |
| 5'4" (163 cm) | 108-145 lbs | 145-173 lbs |
| 5'8" (173 cm) | 122-163 lbs | 164-196 lbs |
| 6'0" (183 cm) | 137-183 lbs | 184-220 lbs |
| 6'4" (193 cm) | 152-204 lbs | 205-245 lbs |
Limitations of BMI
Important: BMI is a screening tool, not a diagnostic measure. It has limitations and should be interpreted by a healthcare professional.
BMI doesn't account for:
- Muscle mass: Athletes may have high BMI due to muscle, not fat
- Age: Older adults may have more body fat at the same BMI
- Gender: Women typically have more body fat than men at the same BMI
- Ethnicity: Health risks vary across ethnic groups at the same BMI
- Fat distribution: Where fat is stored matters for health
Beyond BMI: Other Measures
For a more complete picture, consider these additional measurements:
- Waist circumference: Central obesity indicator
- Waist-to-hip ratio: Fat distribution measure
- Body fat percentage: Actual fat vs. lean mass
- Waist-to-height ratio: Should be less than 0.5
Calculate Your BMI Now
Use our free BMI Calculator for instant results!
Healthy Weight Tips
- Focus on overall health, not just the number on the scale
- Combine regular physical activity with balanced nutrition
- Get adequate sleep (7-9 hours for adults)
- Manage stress through healthy coping mechanisms
- Consult healthcare providers for personalized advice
