BMI Calculator: Calculate Body Mass Index Online
Our free BMI Calculator helps you quickly estimate Body Mass Index from your height and weight. Enter your age, gender, height and weight, choose the unit system that is most convenient for you, and the calculator immediately shows your BMI, category, healthy weight range and visual position on the BMI scale.
This tool is designed for everyday use when you want a quick way to understand how your body weight compares with your height. Instead of manually applying the BMI formula, the calculator handles the unit conversion and calculation for you and presents the result in a clear format that is easy to read on desktop, tablet and mobile devices.
How the BMI Calculator Works
For adults, BMI is calculated by dividing body weight in kilograms by height in meters squared. In simple terms, the formula is BMI = weight ÷ height². For example, a person weighing 65 kg and measuring 1.80 meters has a BMI of about 20.1.
The calculator also converts U.S. measurements when you select the US Units tab. Height can be entered in feet and inches and weight in pounds, while the calculation is internally converted to the metric values needed for the standard BMI formula. The Other Units option provides a simple meter-and-kilogram input format for users who prefer entering height directly in meters.
Understanding Your BMI Result
A BMI result is commonly grouped into four adult categories: underweight below 18.5, normal from 18.5 to 24.9, overweight from 25.0 to 29.9, and obesity at 30.0 or higher. These ranges provide a general screening framework rather than a complete assessment of an individual’s health.
Your result panel highlights the category that contains your calculated BMI and marks the same position on the visual gauge and range chart. The healthy-weight estimate shown by this calculator uses the standard adult BMI interval of 18.5 to 24.9 and applies it to the height entered.
Why BMI Can Be Useful
BMI is popular because it is simple, inexpensive and requires only height and weight. It can be useful as an initial screening number, for tracking broad changes in body weight over time, or for starting a conversation about weight-related health factors.
At the same time, BMI has important limitations. It cannot distinguish muscle from fat, does not show where body fat is stored, and does not account for every factor that affects health. A muscular person, for example, may have a higher BMI because of greater muscle mass rather than excess body fat.
BMI for Different Ages
The adult BMI ranges displayed in the table are intended primarily for adults. For children and teenagers, BMI is interpreted differently because body composition changes as a person grows. Age and sex are considered together with BMI, usually using age-specific growth charts or percentiles rather than the fixed adult categories shown here.
If the calculator is being used for someone under 20, treat the number as a calculated BMI value rather than a diagnosis or an adult weight classification. For health decisions involving children or teenagers, an appropriate pediatric assessment is more useful than applying adult BMI cutoffs.
BMI and Healthy Weight Range
The healthy-weight section gives an estimated weight interval corresponding to a BMI between 18.5 and 24.9 at the entered height. This is a mathematical reference range, not a personalized target. A suitable weight can vary according to age, muscle mass, body composition, activity, medical history and other individual factors.
For a broader view of health and fitness calculations, you can also use our Calorie Calculator, BMR Calculator, Body Fat Calculator and Ideal Weight Calculator. These tools look at different aspects of body measurements and energy needs, so their results should not be treated as interchangeable.
What Can Affect BMI and Body Weight?
Body weight is influenced by many factors, including food intake, physical activity, sleep, age, genetics, muscle mass and lifestyle. Temporary changes can also occur because of hydration, meals, exercise and other everyday factors. For that reason, one BMI result is best viewed as a snapshot rather than a complete picture.
If you are monitoring your weight, using consistent measurement conditions can make changes easier to interpret. For example, taking measurements at similar times and under similar conditions can reduce some of the normal day-to-day variation in body weight.
Use BMI as a Starting Point, Not a Diagnosis
The BMI Calculator is intended as an informational screening tool. A BMI value alone cannot determine whether someone is healthy, nor can it diagnose a medical condition. A more complete assessment may include waist measurement, body composition, blood pressure, fitness, nutrition, medical history and other health indicators.
For that reason, the most useful way to use BMI is as one piece of information alongside other measurements and professional advice when appropriate. If you have concerns about your weight, nutrition or health, a qualified healthcare professional can help interpret the result in the context of your individual situation.
Frequently Asked Questions About BMI
What is a good BMI?
For adults, a BMI from 18.5 to 24.9 is commonly described as the normal or healthy-weight range. However, BMI is only a screening measure and should not be used by itself to judge overall health.
Does BMI work for everyone?
BMI is most useful as a general screening measure for adults. It has limitations for athletes and people with unusually high or low muscle mass, and adult BMI categories should not be applied to children in the same way.
Can I use pounds and feet?
Yes. Select the US Units tab and enter height in feet and inches and weight in pounds. The calculator converts those values automatically before calculating BMI.
Will the graph change when I calculate BMI?
Yes. The BMI value, category, healthy-weight estimate, gauge needle, range marker and highlighted BMI table row all update together when you calculate a new result.