BMI Calculator
Determine your Body Mass Index (BMI) using imperial or metric measurements to understand your weight category.
Last reviewed: June 2026| Category | BMI Range |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 - 24.9 |
| Overweight | 25.0 - 29.9 |
| Obesity Class I | 30.0 - 34.9 |
| Obesity Class II | 35.0 - 39.9 |
| Obesity Class III | 40.0 and above |
Want a more accurate body fat measurement? Try our Body Fat Calculator (US Navy tape method).
Quick Answer
BMI (body mass index) is your weight in kilograms divided by your height in meters squared — or in imperial units, 703 times your weight in pounds divided by your height in inches squared. A BMI of 18.5 to 24.9 is the standard "healthy" range. Enter your height and weight above for an instant result. BMI is a screening tool, not a diagnosis.
How the BMI Calculator works
Body Mass Index is a ratio of weight to height. In metric units, BMI = weight (kg) / height (m)^2. In US units, the equivalent formula is BMI = 703 x weight (lb) / height (in)^2. The calculator converts your entries to kilograms and meters internally, computes BMI, and then maps the result to the standard adult category table.
The adult categories shown here follow CDC cut points for adults 20 and older: underweight below 18.5, healthy weight from 18.5 to less than 25, overweight from 25 to less than 30, and obesity at 30 or greater, with obesity classes beginning at 30, 35, and 40. These categories are screening categories, not diagnoses.
What the extra results mean
The healthy weight range is the weight range that would correspond to BMI 18.5 through 24.9 at the height you entered. The normal BMI range difference tells you how far the entered weight is from that category boundary; it should not be read as a medical instruction to gain or lose that amount.
The estimated body-fat percentage uses the adult Deurenberg equation: body fat % = 1.20 x BMI + 0.23 x age - 10.8 x sex - 5.4, where sex is 1 for male and 0 for female in the original equation. This is only a statistical estimate. It is not the same as DEXA, air displacement, underwater weighing, skinfold measurement, or a clinical body-composition assessment.
Worked examples
5 ft 9 in and 170 lb: height is 69 inches. BMI = 703 x 170 / 69^2, or about 25.1. That falls just inside the adult overweight category. The calculator also shows a healthy-weight range for that height, which is roughly 125 to 168 lb.
175 cm and 77 kg: height is 1.75 m. BMI = 77 / 1.75^2, or about 25.1. The metric result lands in the same adult category because BMI is unit-independent once the conversion is done.
Normal BMI but incomplete picture: a person with BMI 23 can still have high blood pressure, abnormal cholesterol, low muscle mass, or a high waist circumference. A person with BMI 28 can also have substantial muscle mass. BMI is useful because it is quick and consistent, but it is one data point.
When BMI is useful
- Adult screening: it gives a quick weight-for-height category for adults 20 and older.
- Tracking over time: repeated measurements can show broad weight trends when height is stable.
- Population health: BMI is widely used for public-health comparisons because it is inexpensive and easy to collect.
- Conversation starter: it can help frame a clinician discussion alongside blood pressure, labs, waist circumference, history, sleep, medications, and activity.
Common mistakes
- Using adult categories for children: ages 2 through 19 need BMI percentiles that account for age and sex.
- Treating BMI as a diagnosis: CDC describes BMI as a screening measure, not a disease diagnosis.
- Ignoring body composition: BMI does not separate fat mass, muscle mass, bone mass, or where weight is carried.
- Using BMI for pregnancy: pregnancy weight guidance is based on prenatal care context, not this adult BMI category table.
- Using it for employment or insurance decisions: this page is for personal education and health screening context, not eligibility decisions.
Sources
This page is aligned with CDC guidance on what BMI measures and how it should be interpreted, CDC adult BMI categories, CDC's child and teen BMI percentile calculator, and the Deurenberg body-fat prediction equation indexed by PubMed.