Body Mass Index (BMI) Calculator
Calculate your Body Mass Index using metric or imperial units.
No result to display. Please enter your values and calculate.
How the BMI Calculator Works
The BMI Calculator computes your Body Mass Index using your height and weight, then classifies the result into standard BMI categories. It supports both metric (cm, kg) and imperial (ft/in, lb) units and converts everything under the hood so the correct formula is always applied, no matter which input mode you choose.
BMI Formulas (Metric & Imperial)
The calculator uses the universally recognized BMI equations:
- Metric:
BMI = weight (kg) ÷ [height (m)]² - Imperial:
BMI = 703 × weight (lb) ÷ [height (in)]²
In metric mode, your height in centimeters is converted to meters before the calculation. In imperial mode, your height in feet and inches is converted to total inches, and the 703 factor is applied. The final BMI value is typically shown to one decimal place for clarity.
BMI Categories & Interpretation
Once your BMI is calculated, the tool maps it to common adult categories:
- Underweight: BMI < 18.5
- Normal weight: BMI 18.5–24.9
- Overweight: BMI 25–29.9
- Obese: BMI ≥ 30
Your result is displayed in a highlighted card along with its category, and a visual chart positions your BMI along the range so you can quickly see where you fall.
What BMI Tells You (and What It Doesn’t)
BMI is a screening tool, not a diagnosis. It is useful for:
- Getting a quick indication of whether your weight may be in a higher- or lower-risk range.
- Population-level comparisons and public health tracking.
- Starting conversations about lifestyle, nutrition, and health goals.
However, BMI does not distinguish between muscle and fat mass, and it does not account for age, sex, ethnicity, bone structure, athletic build, or fat distribution. Very muscular people may have a high BMI but low body fat; others may have a "normal" BMI but elevated health risks.
Scope & Assumptions
To keep the results accurate and easy to interpret, this BMI Calculator:
- Is intended primarily for adults 18+.
- Assumes valid, positive height and weight values; invalid entries are rejected with clear messages.
- Uses standard adult BMI cutoffs and does not implement pediatric growth charts.
- Does not factor in medical history, lab results, or body composition measurements.
Educational Insight
BMI is best viewed as one data point, not the whole picture. This BMI Calculator makes the math instant and transparent so you can see how your height and weight combine into a single index, then take that number into context with guidance from healthcare professionals, waist measurements, activity levels, and overall lifestyle.