How to Use the BMI Calculator
This calculator computes body mass index (BMI) and categorizes the result for adults and children. It supports metric (kilograms and centimeters), imperial (pounds and feet/inches), and a child/teen mode that uses CDC BMI-for-age percentile data. BMI is a screening tool, not a diagnostic of body fatness or health. Consult a healthcare provider for a complete assessment.
Calculation Modes
Metric
Enter your weight in kilograms and height in centimeters. The calculator computes your BMI, weight category, and healthy weight range.
Formula: BMI = Weight (kg) / [Height (m)]^2
Adult categories:
- Underweight: below 18.5 (blue)
- Healthy Weight: 18.5 to 25 (green)
- Overweight: 25 to 30 (orange)
- Obese: 30 and above (red)
Example: 70 kg, 175 cm
- Weight: 70
- Height: 175
- BMI: 22.857143
- Category: Healthy Weight
- Healthy Weight Range: 56.65625 - 76.25625 kg
After calculating, a BMI breakdown table shows your BMI, category (color-coded), and healthy weight range. Below it, a BMI categories table lists all four categories with your current one highlighted.
Example: 85 kg, 165 cm
- Weight: 85
- Height: 165
- BMI: 31.221304
- Category: Obese
- Healthy Weight Range: 50.36625 - 67.79025 kg
Imperial
Enter your weight in pounds and height as feet plus inches. The calculator computes your BMI, weight category, and healthy weight range.
Formula: BMI = 703 x Weight (lbs) / [Height (in)]^2
Example: 154 lbs, 5 feet 9 inches
- Weight: 154
- Height (ft): 5
- Height (in): 9
- BMI: 22.73934
- Category: Healthy Weight
- Healthy Weight Range: 125.28947 - 168.63286 lbs
After calculating, a BMI breakdown table shows your BMI, category (color-coded), and healthy weight range. Below it, a BMI categories table lists all four categories with your current one highlighted.
Example: 200 lbs, 5 feet 6 inches
- Weight: 200
- Height (ft): 5
- Height (in): 6
- BMI: 32.277319
- Category: Obese
- Healthy Weight Range: 114.63158 - 154.28791 lbs
Child/Teen
For children and adolescents ages 2 to 20, BMI is interpreted using CDC growth chart percentiles rather than fixed adult thresholds. Enter age, gender, weight in kilograms, and height in centimeters. The calculator compares the BMI against CDC BMI-for-age growth chart data for the nearest half-month age point and selected gender.
Formula: BMI = Weight (kg) / [Height (m)]^2
Categories:
- Underweight: BMI below 5th percentile (blue)
- Healthy Weight: 5th to 84th percentile (green)
- Overweight: 85th to 94th percentile (orange)
- Obese: 95th percentile and above (red)
Example: 12-year-old male, 45 kg, 150 cm
- Age: 12
- Gender: male
- Weight: 45
- Height: 150
- BMI: 20
- Category: Healthy Weight
- Estimated Percentile: 72nd
After calculating, a BMI breakdown table shows your BMI, age, gender, category (color-coded), and estimated percentile. Below it, a BMI categories table lists all four categories with your current one highlighted.
Example: 8-year-old female, 32 kg, 125 cm
- Age: 8
- Gender: female
- Weight: 32
- Height: 125
- BMI: 20.48
- Category: Overweight
- Estimated Percentile: 94th
Precision and Notation Settings
Use the settings bar above the tabs to control how results display:
- Decimal places: Adjust from 0 to 16 decimal places (default is 8)
- Notation: Switch between auto, fixed, exponential, and engineering notation (default is auto)
Your decimal places and notation settings save to your browser automatically. When you return to this calculator, your last chosen format loads without needing to adjust it again.
Common Use Cases
Routine Health Check
You are 68 kg and 172 cm tall:
- Switch to Metric
- Enter 68 as Weight, 172 as Height
- BMI: 22.985397
- Category: Healthy Weight
Using Imperial Measurements
You weigh 180 lbs and are 5 feet 10 inches:
- Switch to Imperial
- Enter 180 as Weight, 5 as Height (ft), 10 as Height (in)
- BMI: 25.824489
- Category: Overweight
Checking a Child's Growth
Your 10-year-old daughter is 35 kg and 140 cm:
- Switch to Child/Teen
- Enter 10 as Age, female as Gender, 35 as Weight, 140 as Height
- BMI: 17.857143
- Category: Healthy Weight
- Estimated Percentile: 61st
Finding Your Healthy Weight Range
You are 180 cm tall and want to know your healthy weight range:
- Switch to Metric
- Enter any weight (for example, 75) and 180 as Height
- Healthy Weight Range: 59.94 - 80.676 kg
Tips for Accurate Calculations
- Use accurate measurements: BMI is sensitive to height. A 2 cm difference can shift your BMI
- Child/teen mode requires age 2 to 20: Ages outside this range are rejected because CDC data only covers this span
- Select the correct gender for children: Boys and girls have different growth curves
- Healthy weight range is for adults only: child/teen mode does not show a range because children grow at different rates
- Imperial height requires both fields: Enter feet and inches separately. If you are exactly 6 feet, enter 6 for feet and 0 for inches
- Child/teen percentiles are estimated: interpolated between CDC data points, not an exact clinical measurement
- BMI has limitations: it does not distinguish muscle from fat
Troubleshooting
Required
This appears when a field is left empty. Enter a value in all required fields before calculating.
Weight must be positive
Enter a positive weight. Zero or negative weights are not valid.
Height must be positive
Enter a positive height. Zero and negative heights are rejected.
Age must be between 2 and 20
The child/teen mode only supports ages 2 through 20. For adults, use metric or imperial mode.
Please select a gender
In child/teen mode, you must select male or female from the dropdown.
Height (feet) cannot be negative
In imperial mode, the feet portion of height cannot be negative.
Height (inches) cannot be negative
In imperial mode, the inches portion of height cannot be negative.
Height must be greater than 0
In imperial mode, your total height must be greater than zero. If you enter 0 for both feet and inches, the calculator rejects it.
Breakdown table not appearing
The details section renders after a successful calculation with no validation errors. Check that all required inputs are filled and valid, then click Calculate.