Underweight
May indicate nutritional deficiency or other health concerns — discuss results with a clinician if unexpected.
Fitness & health
BMI Calculator
Calculate Body Mass Index from height and weight, then see the WHO adult weight category.
Your Measurements
Switch between US and metric units. BMI uses the standard adult formula from WHO/CDC references.
Height (feet)
Height (inches)
Weight (pounds)
Height (cm)
Weight (kg)
Age (optional)
Gender (optional)
BMI Formula & Categories
US units use BMI = 703 × weight(lb) / height(in)². Metric uses BMI = weight(kg) / height(m)². Adult categories below follow World Health Organization ranges.
Normal
Generally considered a healthy BMI range for most adults when paired with good lifestyle habits.
Overweight
Associated with higher risk of several chronic conditions; waist size and fitness still matter.
Obesity
WHO classes I–III begin at BMI 30, 35, and 40 respectively and warrant personalized medical guidance.
BMI Calculator Features
Quickly convert height and weight into BMI, category, and related indices.
US & Metric Units
Switch between feet/inches/pounds and centimeters/kilograms without leaving the page.
WHO Classification
See thinness, normal, overweight, and obesity class labels update as you change inputs.
Healthy Weight Range
Estimate the weight band that corresponds to BMI 18.5–25 for your height.
BMI Prime & Ponderal Index
Optional extras: BMI relative to 25, plus a cubing-based lean-mass style index.
Understanding BMI Limitations
BMI is a screening tool based on height and weight — not a complete health diagnosis.
Muscle vs. fat
Athletes and highly muscular people can land in the overweight range despite low body fat. Conversely, someone with low muscle mass may look “normal” while carrying excess fat.
Age and sex
Body composition shifts with age, and women often have higher body-fat percentages than men at the same BMI. Clinical context matters more than a single number.
Children and teens
Ages 2–20 typically use BMI-for-age percentiles rather than adult cutoffs. This calculator applies adult WHO categories and is intended for adult screening.
What to do next
Use BMI as a conversation starter with a healthcare professional. Waist circumference, blood pressure, labs, and fitness assessments provide a fuller picture.
Why Use Our BMI Calculator?
- Standard US and metric BMI formulas used by public-health references
- Clear WHO adult categories with an on-page visual meter
- Healthy weight range, BMI Prime, and Ponderal Index in one place
- Free, private, and instant — nothing to download or install
Frequently Asked Questions
How do I calculate BMI manually?
In metric units, divide weight in kilograms by height in meters squared. In US units, multiply weight in pounds by 703, then divide by height in inches squared.
What is a healthy BMI for adults?
WHO generally treats 18.5 to under 25 as the normal range for adults. Individual targets can differ based on medical history — ask a clinician for personal advice.
What is BMI Prime?
BMI Prime is your BMI divided by 25 (the upper end of the normal adult range). A value near 1.0 means you are around that reference point; above 1.0 indicates overweight territory on this scale.
What is the Ponderal Index?
It is similar to BMI but uses height cubed instead of squared. Some researchers prefer it for very tall or short individuals, though it still does not measure body fat directly.
Can BMI diagnose obesity-related disease?
No. BMI screens for weight categories. Diagnosis of metabolic disease requires clinical evaluation, not a calculator alone.
Why does my category change between US and metric?
It should not if measurements are equivalent. Rounding differences can cause tiny BMI shifts near a boundary (for example 24.9 vs 25.0). Double-check conversions if results disagree.
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Disclaimer
BMI does not measure body fat directly and can misclassify muscular, elderly, pregnant, or medically complex individuals. This tool is not medical advice — consult a healthcare professional for personal guidance.