BMI Calculator
Enter your height and weight to instantly calculate your BMI (Body Mass Index) and assess your weight status.
How to Use
- Enter your height in centimeters (cm) in the "Height" field, e.g., 170.
- Enter your weight in kilograms (kg) in the "Weight" field, e.g., 65.
- Click "Calculate BMI" to instantly view your BMI value and weight classification.
- Click "Reset" to clear all fields and start over.
BMI Formula
BMI = Weight (kg) ÷ Height (m)²Height must be in meters. For example, a height of 170 cm should be converted to 1.70 m before applying the formula.
BMI Classification Standards
The table below compares the WHO international standard with Taiwan's Ministry of Health and Welfare standard. Taiwan has lower thresholds for overweight and obesity due to the body composition characteristics of Asian populations.
| Weight Status | WHO International Standard | Taiwan MOHW Standard |
|---|---|---|
| Underweight | BMI < 18.5 | BMI < 18.5 |
| Normal | 18.5 ≤ BMI < 25 | 18.5 ≤ BMI < 24 |
| Overweight | 25 ≤ BMI < 30 | 24 ≤ BMI < 27 |
| Obese | BMI ≥ 30 | BMI ≥ 27 |
Calculation Example
Given:Height 170 cm, Weight 65 kg
Step 1:Convert height to meters → 170 cm = 1.70 m
Step 2:Apply the formula → BMI = 65 ÷ (1.70 × 1.70) = 65 ÷ 2.89 ≈ 22.5
Result:BMI is 22.5, which falls in the "Normal" range (Taiwan standard: 18.5–24).
Important Notes
- Athletes:People with high muscle mass may have an elevated BMI without being overweight. Consider measuring body fat percentage as well.
- Pregnant women:Weight gain during pregnancy is normal, and BMI is not suitable for assessing weight during this period.
- Elderly:For adults over 65, the normal BMI range can be relaxed to 18.5–27 due to age-related muscle loss.
- Children and adolescents:Growing children should use age-specific BMI percentile charts rather than adult standards.
- Fat distribution:BMI does not reflect abdominal fat accumulation. It is recommended to also measure waist circumference (men < 90 cm, women < 80 cm).
- This calculator is for reference only and cannot replace professional medical diagnosis. Please consult a doctor if you have health concerns.
Frequently Asked Questions
What is BMI (Body Mass Index)?
BMI (Body Mass Index) is a numerical value calculated from height and weight, used to assess whether a person's weight is within a healthy range. The formula divides weight in kilograms by the square of height in meters. BMI is a globally recognized screening tool adopted by the WHO and health agencies worldwide.
What is the normal BMI range? How do Taiwan and international standards differ?
According to Taiwan's Ministry of Health and Welfare, a normal BMI ranges from 18.5 to 24, while the WHO international standard is 18.5 to 25. Taiwan has lowered the overweight threshold from 25 to 24 and the obesity threshold from 30 to 27 to better reflect the health risks specific to Asian populations.
What are the limitations of BMI? Who should not rely on it?
BMI cannot distinguish between fat and muscle mass, so it may produce inflated results for athletes and bodybuilders. It is also not suitable for pregnant women, growing children and adolescents, or adults over 65. A comprehensive assessment should include waist circumference and body fat percentage.
How can I lower my BMI? What are healthy weight loss methods?
The key to lowering BMI is maintaining a caloric deficit (consuming fewer calories than you burn). A balanced diet, reducing refined sugars and processed foods, at least 150 minutes of moderate aerobic exercise per week, and strength training are recommended. Avoid extreme dieting and aim for a healthy target of 0.5–1 kg per week. Consult a nutritionist or doctor during the process.
What is the difference between BMI and body fat percentage?
BMI is calculated solely from height and weight and cannot differentiate between fat and muscle. Body fat percentage directly measures the proportion of body fat, providing a more accurate picture of body composition. The ideal body fat percentage is 15%–25% for adult men and 20%–30% for adult women. Using both metrics together provides a more comprehensive health assessment.