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BMI Calculator: Body Mass Index for Men, Women & Children

Use our free Body Mass Index (BMI) calculator to assess your weight status. Whether you're an adult, teenager, or child, this tool helps you understand your BMI and ideal weight range.

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What is Body Mass Index (BMI)?

Body Mass Index (BMI) is a simple measure that uses your height and weight to estimate body fat and screen for weight categories that may lead to health problems. It is widely used for adults, but also interpreted differently for children and teens (percentiles).

BMI categories for adults (ages 20+) are independent of gender and age:

  • Underweight: BMI less than 18.5
  • Normal weight (healthy): BMI 18.5 – 24.9
  • Overweight: BMI 25 – 29.9
  • Obese: BMI 30 or greater

While BMI is a useful screening tool, it does not directly measure body fat and may not be accurate for athletes, pregnant women, or the elderly.

BMI Formula and Calculation

Metric formula: BMI = weight (kg) / [height (m)]²
Imperial formula: BMI = (weight (lbs) / [height (in)]²) × 703

For metric, convert height from centimeters to meters by dividing by 100. For imperial, convert feet and inches to total inches (1 ft = 12 in).

BMI Example: How to Calculate

Metric example: A person weighing 70 kg and 175 cm tall.
Height in meters = 175 / 100 = 1.75 m
BMI = 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.86 → Normal weight.

Imperial example: A person weighing 154 lbs and 5'9" (69 inches).
BMI = (154 / (69)²) × 703 = (154 / 4761) × 703 ≈ 0.03234 × 703 ≈ 22.74 → Normal weight.

Step-by-Step Guide to Compute BMI

  1. Measure your height accurately (in cm or feet/inches).
  2. Measure your weight (in kg or lbs).
  3. If using metric: convert height to meters (divide cm by 100).
  4. If using imperial: convert height to total inches (feet × 12 + inches).
  5. Square your height (multiply it by itself).
  6. Divide your weight by the squared height.
  7. If using imperial, multiply the result by 703.
  8. The final number is your BMI. Compare with the categories above.

Frequently Asked Questions About BMI

❓ What is a healthy BMI range for adults?
A BMI between 18.5 and 24.9 is considered healthy. Below that is underweight, and above is overweight or obese.

❓ Is BMI accurate for athletes and bodybuilders?
BMI may overestimate body fat in muscular individuals because muscle weighs more than fat. In such cases, body fat percentage measurements are more reliable.

❓ How do I calculate BMI for children and teenagers?
The same formula is used, but the result is compared to age-and-gender percentiles (BMI-for-age charts). Consult a pediatrician for interpretation.

❓ Can I use this calculator if I am pregnant?
BMI is not accurate during pregnancy due to weight gain and body composition changes. Speak with your healthcare provider.

❓ What is the ideal weight for my height?
Based on a healthy BMI (18.5-24.9), your ideal weight range is:
Minimum healthy weight (kg) = 18.5 × (height in m)²
Maximum healthy weight (kg) = 24.9 × (height in m)²
You can see this range in the results above.

❓ Why does my BMI matter?
Maintaining a healthy BMI reduces the risk of chronic diseases such as heart disease, diabetes, and hypertension.