BMI and Healthy Weight Calculator

BMI and Healthy Weight Calculator

BMI (Body Mass Index) is a weight assessment indicator calculated from height and weight. It can be used to gain an initial understanding of the relationship between body weight and height. This tool provides online BMI calculations for adults and children. Enter age, sex, height and weight to view your BMI, weight category and related healthy weight reference values.

Adult BMI Calculation

Adult BMI is calculated from body weight and height and is commonly used for an initial assessment of whether weight falls into the underweight, normal weight, overweight or obesity range. This tool uses commonly referenced BMI categories for adults in China:

• BMI < 18.5: Underweight.
• 18.5 ≤ BMI < 24: Normal weight.
• 24 ≤ BMI < 28: Overweight.
• BMI ≥ 28: Obesity.

These are commonly used reference categories for adults in China, not universal global standards. Different countries, regions and professional organizations may use different BMI thresholds.

Child and Adolescent BMI Calculation

Children and adolescents are still growing and developing, so BMI varies with age and sex. Adult BMI thresholds should therefore not be applied directly to children. Based on the age and sex entered, this tool references the US CDC BMI-for-age growth standards for ages 2–20 and calculates the BMI percentile, Z-score and corresponding category reference.

A child’s BMI percentile compares their BMI with that of a reference population of the same age and sex. Under commonly used CDC categories, below the 5th percentile is classified as underweight, from the 5th to below the 85th percentile as healthy weight, from the 85th to below the 95th percentile as overweight, and at or above the 95th percentile as obesity. Percentiles are screening references and should not be used alone to diagnose a child’s nutritional or health status.

BMI Calculation Formula

The basic BMI formula is:

BMI = Weight (kg) ÷ Height (m)²

For example, if height is 170 cm and weight is 65 kg, convert the height to 1.70 m first, then calculate: 65 ÷ (1.70 × 1.70). The BMI is approximately 22.49.

Which Healthy Weight Metrics Can You Calculate?

• BMI: Calculates body mass index from the entered height and weight.
• BMI Category: Displays a category based on the applicable adult or child reference standard.
• Healthy Weight Range: Estimates a corresponding weight range based on adult BMI reference values and height.
• Standard Weight: Estimates standard weight using commonly used formulas for weight management reference.
• Ideal Weight: Provides a weight reference calculated using height and other relevant data.
• Estimated Body Fat Percentage: Estimates body fat percentage using a formula based on BMI, age and sex; this is not a direct body fat measurement.
• Child BMI Percentile: Provides a child BMI growth percentile reference based on age and sex.

How to Use the BMI Calculator

1. Select adult or child calculation mode.
2. Select sex and enter the corresponding age. In child mode, you can also enter the number of months.
3. Choose metric or imperial units, then enter height and weight.
4. Click “Calculate” to view BMI, category and related weight reference values.
5. Review the health analysis, dietary suggestions and exercise recommendations based on the results.

Metric and Imperial Unit Support

This tool supports both metric and imperial units. Metric inputs use centimeters (cm) and kilograms (kg), while imperial inputs use feet (ft), inches (in) and pounds (lb). After switching units, you can enter height and weight using the selected units without manual conversion.

How Should You Interpret BMI Results?

BMI is a simple weight screening indicator. It does not directly measure body fat distribution, muscle mass or body composition. For example, someone with greater muscle mass may have a higher BMI without necessarily having excess body fat. Adult BMI should therefore be interpreted alongside waist circumference, body composition, lifestyle and other health indicators.

Children and adolescents are also affected by age, sex and stage of growth and development. Their BMI should be assessed using the relevant BMI-for-age percentile and considered in the context of ongoing growth. Do not restrict a child's diet or initiate weight-loss interventions based solely on a single calculation.

Results and Health Disclaimer

Standard weight, ideal weight and body fat percentage provided by this tool are formula-based estimates or reference indicators, not medical measurements. BMI categories alone cannot determine whether someone has a particular disease. Results are for general health management reference only. If you have persistent weight concerns, nutritional issues or other health questions, consult a doctor or registered dietitian.

Privacy and Data Processing

Height, weight, age and sex are processed locally in your browser. They are not uploaded to the server, and no account registration is required. The tool's analytics interface only records tool usage and does not submit the body measurements or personal data entered above.