Medically Reviewed & Supervised By
Gina Pastore, APRN-BC, MSN, ABAAHP
Board-Certified Adult Nurse Practitioner | ABAAHP Diplomate, A4M | 30+ Years Healthcare Experience | 20+ Years Hormone Specialization
MSN, University of South Florida · FL APRN License — Active & Verified
Find Your BMI
To get your BMI, select metric or imperial units and enter your current height and weight. The calculator divides your weight by your height squared and places the answer in one of the standard adult weight categories. For a reliable reading, weigh yourself on a flat, hard floor without shoes or heavy clothing, and measure your height standing straight against a wall. The categories shown apply to adults 20 and over. They are not designed for children, teenagers, or pregnant women, and they can misjudge very muscular or older adults.
Keep in mind that BMI is a broad screening measure. The sections further down explain what it can and cannot show, and our body fat calculator fills in some of the gaps.
BMI Categories Explained
The World Health Organization defines the adult BMI categories listed here, and the CDC uses the same ones. They are intended for people aged 20 and up. Think of them as a first-pass health check, since no category amounts to a medical diagnosis.
| Category | BMI | What It Means |
|---|---|---|
| Underweight | Under 18.5 | Could reflect too little nourishment, thinning bones, or a health problem that needs attention. Have it looked into. |
| Healthy Weight | 18.5 to 24.9 | The standard target zone for adults. Two people here can still have very different metabolic health. |
| Overweight | 25.0 to 29.9 | Type 2 diabetes and heart disease become more likely, especially if most of the weight sits at the midsection. |
| Obesity Class 1 | 30.0 to 34.9 | The level at which medical weight loss, including GLP-1 medication, typically enters the discussion. |
| Obesity Class 2 | 35.0 to 39.9 | Risk climbs further. Treatment generally becomes more involved, with regular check-ins. |
| Obesity Class 3 | 40.0 or more | Often referred to as severe obesity. Tied to much higher risk affecting nearly every organ system. |
Adult categories from the World Health Organization. For ages 20 and over.
The Math Behind BMI
Only two measurements go into your BMI. Below you will find the equation, a short history of where it came from, and the things it leaves out.
With metric units, take your weight in kilograms and divide it by your height in meters multiplied by itself. With imperial units, take your weight in pounds, divide by your height in inches multiplied by itself, and multiply the answer by 703.
The idea dates to the 1830s, when Belgian statistician Adolphe Quetelet created it to describe trends across whole populations. He did not design it to assess any single person. Medicine picked it up in the twentieth century for practical reasons: it is free, quick, and requires nothing more than a scale and a tape measure.
BMI treats every pound the same. It cannot see whether your weight is muscle or fat, or whether fat is stored around your organs. Athletes can score high with little body fat, and people with low muscle can score normal while carrying too much. Body fat percentage, waist measurement, and blood work help complete the picture.
How BMI Affects Treatment Options
Imperfect as it is, BMI is still the measure most medical weight loss criteria rely on. Semaglutide, tirzepatide, and other GLP-1 medications are usually considered for adults whose BMI is 30 or more. The threshold drops to 27 for people who also have a weight-related condition, such as high blood pressure, type 2 diabetes, or high cholesterol.
Reaching that threshold is the first step, not the final word. A provider reviews your lab results and medical history during a consultation before confirming that you qualify and deciding whether medication is the right approach for you.
BMI flags a possible concern. A consultation explains it. We review your labs, hormone levels, and health history, then build a treatment plan around what we find.
