How to Use the BMI Calculator
Follow these steps:
- Enter your height and weight, choosing the unit beside each value.
- Click Calculate BMI. The result appears after the values pass validation.
- Click Reset to clear the fields and hide the result. Changing a unit also hides the current result.
What the Result Includes
The result shows BMI to one decimal place and the matching weight category. The category uses the unrounded BMI value. It also shows the entered values and the metric height and weight used. Imperial entries are converted with 1 in = 2.54 cm and 1 lb = 0.45359237 kg.
The result includes BMI = weight (kg) / height (m)^2, the assumptions used, and a category-threshold table:
- BMI < 18.5: Underweight
- BMI < 25: Normal weight
- BMI < 30: Overweight
- Otherwise: Obese
Copying or Downloading the Result
Click Copy result to copy the plain-text summary. If copying fails, the tool shows a message telling you to select and copy it manually. Click Download result (.txt) to save a text file.
The text output includes the unit system, entered values, metric values, BMI, category, and disclaimer. It does not include the formula or the category-threshold table shown in the result section.
Validation and Input Limits
Height and weight must be finite, positive numbers. The selected unit beside each value determines its conversion before calculation.
The inches field displays max="11", but the JavaScript validation does not enforce that maximum. Values above 11 inches may therefore be processed.
Limitations and Privacy Scope
BMI is a screening ratio based on height and weight, not a diagnosis. This calculation does not account for muscle mass, bone density, body fat distribution, age, sex, or ethnicity.
The BMI calculation runs in browser-side JavaScript, and the inspected calculator script does not send BMI inputs to a server. This does not establish a broader privacy guarantee for the page, which also loads analytics and includes a server-posted subscription form.
BMI Calculator FAQ
How is BMI calculated?
BMI is calculated as weight in kilograms divided by height in meters squared (BMI = kg / m^2). If you enter imperial units, height and weight are first converted to metric before applying the same formula.
What do the BMI categories mean?
This tool uses these adult category comparisons: BMI < 18.5 is Underweight, BMI < 25 is Normal weight, BMI < 30 is Overweight, and otherwise the category is Obese.
Is BMI accurate for everyone?
No. BMI is a simple screening ratio based only on height and weight. It does not account for muscle mass, bone density, body fat distribution, age, sex, or ethnicity, and can misclassify athletes, older adults, and other groups. It is not a diagnosis.
Can I use imperial units instead of metric?
Yes. Choose cm, ft, or in beside Height and kg or lb beside Weight. The values are converted to metric internally before the BMI formula is applied, and the conversion is shown in the result.
What happens if I enter an invalid height or weight?
Calculation stops and an error message appears when height or weight is missing, zero, negative, or invalid. The selected units beside the values determine their conversion before the BMI formula is applied.