BMI Calculator
BMI Categories for Adults
| Category | BMI Range |
|---|---|
| Underweight | < 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese | ≥ 30.0 |
BMI Percentiles for Children & Teens
| Category | Percentile Range |
|---|---|
| Underweight | < 5th percentile |
| Normal weight | 5th – 84th percentile |
| Overweight | 85th – 94th percentile |
| Obese | ≥ 95th percentile |
BMI Formula
BMI = Weight (kg) ÷ Height (m)²BMI = 703 × Weight (lbs) ÷ Height (in)²What Is BMI?
Body Mass Index (BMI) is a numerical value calculated from a person's weight and height. It provides a quick screening method to categorize individuals into weight classes — underweight, normal weight, overweight, or obese — and is widely used by healthcare professionals to assess whether a person's weight may pose health risks.
BMI was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is sometimes referred to as the Quetelet Index. While it does not directly measure body fat, research has shown that BMI correlates moderately well with body fat percentage measured through more precise methods such as DEXA scans and underwater weighing.
A healthy BMI for adults typically falls between 18.5 and 24.9. Values below 18.5 suggest the person may be underweight, while values of 25 or above indicate overweight or obesity, both of which are associated with higher risks for cardiovascular disease, type 2 diabetes, and certain cancers.
How to Calculate BMI
To calculate BMI using the metric system, divide your weight in kilograms by the square of your height in metres. For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.
Using the imperial system, multiply your weight in pounds by 703 and then divide by the square of your height in inches. For example, a person who weighs 154 lbs and is 69 inches tall has a BMI of (703 × 154) ÷ (69 × 69) = 22.7.
This calculator performs the computation instantly — simply enter your weight and height in whichever unit system you prefer, and your BMI, category, and healthy weight range appear in real time.
Limitations of BMI
While BMI is a useful population-level screening tool, it has several important limitations at the individual level. It does not distinguish between fat mass and lean mass, which means muscular individuals — such as athletes and bodybuilders — often receive an "overweight" classification despite having low body fat.
BMI also does not account for age, sex, ethnicity, or fat distribution. Abdominal fat (visceral fat) carries greater health risks than fat stored in the hips and thighs, but BMI cannot differentiate between the two. For a more complete health picture, consider complementing your BMI result with measurements like waist circumference, body fat percentage, or a consultation with a healthcare professional.
Frequently Asked Questions
What is a good BMI?
A BMI between 18.5 and 24.9 is considered normal weight by the World Health Organization. This range is associated with the lowest overall health risks. However, "good" depends on individual factors like muscle mass, bone density, and overall fitness level.
Is BMI the same for men and women?
The BMI formula and category thresholds are the same for both men and women. However, women naturally carry a higher percentage of body fat than men at the same BMI, which means the health implications of a given BMI value can differ between sexes.
Can BMI be inaccurate for athletes?
Yes. Athletes, bodybuilders, and highly active individuals often have above-average muscle mass, which increases body weight without increasing fat. As a result, their BMI may classify them as overweight or obese even though their body fat percentage is low and their health is excellent.
How often should I check my BMI?
Checking your BMI once every few months is sufficient for most adults. If you are actively working to gain or lose weight, tracking monthly can help you monitor progress. Pairing BMI with other metrics like waist circumference or body fat percentage provides a more complete view of your health.
Does BMI apply to children?
BMI for children and teens (ages 2–19) is age- and sex-specific. Instead of fixed thresholds, it is expressed as a percentile relative to other children of the same age and sex. A BMI at or above the 85th percentile is considered overweight, while at or above the 95th percentile is classified as obese.
How to Use the BMI Calculator
Using the BMI Calculator is straightforward and designed for instant results. Simply input your required values into the designated fields above. The calculator will automatically process the inputs in real-time, applying the necessary mathematical formulas to provide an accurate, step-by-step breakdown (where applicable) instantly. If you input invalid data, clear error messages will guide you.
Formula & Methodology
This tool utilizes standard, universally accepted mathematical formulas to ensure 100% accuracy. Our methodology guarantees that edge cases—such as division by zero, negative roots, or complex numbers—are handled gracefully according to strict mathematical principles.
Common Examples
Whether you are a student verifying homework, a professional calculating technical specifications, or simply solving everyday math problems, this calculator eliminates manual errors. It replaces tedious handwritten calculations with instant, verifiable logic.
Frequently Asked Questions
Is the BMI Calculator free to use?
Yes, this tool is 100% free, requires no registration, and contains zero intrusive ads.
How accurate are the results?
The calculations are performed using high-precision JavaScript mathematical libraries, ensuring accuracy up to 10 decimal places where applicable.