BMI Calculator — Free Body Mass Index Tool

How to use BMI Calculator — Free Body Mass Index Tool

Three simple steps, with your content kept on your device.

Built for useful work

Fast, focused, and made to be clear on every screen.

What is BMI?

BMI, or body mass index, is a simple number that relates weight to height. It is one of the oldest and most widely used screening tools for classifying body weight in adults, because it needs only two measurements and no laboratory equipment.

BMI is a screening indicator, not a diagnosis. It gives a quick first signal about whether a person's weight sits in a typical range for their height, which is why doctors, insurers, and public-health bodies still use it as a starting point.

The BMI formula

Metric BMI divides weight in kilograms by height in meters squared: BMI equals weight divided by height squared. A 70 kilogram person who is 1.75 meters tall has a BMI of about 22.9.

The US formula performs the same calculation after converting pounds and inches into metric units, so both unit systems produce the same classification.

Understanding BMI categories

Common adult categories classify a BMI under 18.5 as underweight, 18.5 to 24.9 as healthy, 25 to 29.9 as overweight, and 30 and above as obese. These bands come from population-level studies and are the standard reference points.

This calculator places your result on the same scale and shows the healthy-weight range for your height, so you can see where the number falls at a glance.

Limitations of BMI

BMI does not distinguish muscle from fat, so an athlete with high muscle mass can be classified as overweight despite being lean. It also does not account for where fat is distributed, age, or ethnicity.

Adult BMI categories are not designed for children, pregnancy, or individualized assessment of medical conditions. BMI should be interpreted together with other measurements and professional advice, never alone.

How to use this calculator

Enter your height and weight in metric or US units, and the tool calculates BMI, shows the category, and lists the healthy-weight range for your height. The calculation runs entirely in your browser, so your measurements never leave your device.

For the most meaningful reading, measure height and weight consistently and use the same units for both inputs.

BMI for men and women

The same BMI formula and the same adult categories apply to both men and women. Because BMI compares weight to height, the calculation itself does not use gender, age, or body frame.

Interpretation can differ in practice — muscle mass, body composition, and ethnicity all influence what a given BMI means for an individual — but the number and its standard bands are computed identically.

Healthy weight range for your height

The healthy-weight range is the set of weights that falls inside the 18.5 to 24.9 BMI band for a given height. This calculator shows that range alongside your result, so you can see how far a current weight sits from the middle of the healthy band.

The range is a general guideline for typical adults, not a target for everyone. Individual health depends on many factors that a weight-to-height ratio alone cannot capture.

BMI for children and teens

Children and teenagers are not classified with the adult BMI bands, because their body composition changes as they grow. For people under 18, BMI is compared against age- and sex-specific growth charts instead.

This calculator is built for adults. If you need a BMI for a child or teen, use a pediatric growth chart with a doctor or a tool designed for that age group.

What to do with your BMI result

A single BMI number is a starting point, not a verdict. If your result falls outside the healthy band, the useful next step is a conversation with a healthcare professional who can consider muscle mass, waist circumference, activity level, and medical history.

For most people, steady habits — balanced eating, regular movement, and enough sleep — matter far more than any single measurement.

Frequently asked questions