A fast, no-signup BMI calculator
You should not have to create an account just to check a number. With this
online BMI calculator you simply choose US or metric units, enter your
height and weight, and read your result. It works on phones, tablets, and
desktops, and it loads quickly because the page is lightweight by design.
How the online calculation works
The tool applies the standard BMI formula directly in your browser using a
small amount of JavaScript. In metric, that is weight in kilograms divided
by height in metres squared; in US units, it is weight in pounds divided by
height in inches squared, multiplied by 703. Because the calculation is
local, nothing you type is uploaded anywhere.
Adult BMI categories
Adult BMI categories for ages 20 and older | Category | BMI range |
| Underweight | Below 18.5 |
| Healthy Weight | 18.5 - 24.9 |
| Overweight | 25.0 - 29.9 |
| Obesity | 30.0 and above |
| Class 1 Obesity | 30.0 - 34.9 |
| Class 2 Obesity | 35.0 - 39.9 |
| Class 3 Obesity | 40.0 and above |
Your privacy
We designed this calculator so your height, weight, and age never leave
your device. There is no server-side processing of your inputs and no
database storing your results. If you close the tab, the numbers are gone.
You can read more in our Privacy Policy.
What the result can and cannot tell you
An online BMI result is an accurate report of your BMI for the numbers you
entered, and a helpful screening signal. It is not a diagnosis and cannot
separate muscle from fat. For anything affecting your health decisions,
confirm with a healthcare provider.
Frequently asked questions
What is a BMI calculator?
A BMI calculator is a simple tool that estimates your Body Mass Index from your height and weight. BMI is a screening measure used to place adults into broad weight categories. It does not measure body fat directly and does not diagnose any health condition - it is a starting point for a conversation with a healthcare provider.
How do you use this BMI calculator?
Choose US units or metric units with the toggle, enter your height and weight, optionally add age and sex for context, then select Calculate. Your BMI and adult category appear instantly. Nothing you type is sent anywhere - the calculation happens entirely in your browser.
Is my height and weight kept private?
Yes. The calculator runs entirely in your browser using JavaScript. Your height, weight, age, and any other input are never sent to a server or stored by us, so your measurements stay on your device.
Is a BMI calculator accurate?
A BMI calculator accurately reports the BMI number for the height and weight you enter. As a health measure, BMI is a useful screening tool for populations, but it has limits for individuals: it does not separate muscle from fat and does not account for where fat is stored. It is best used as a quick check, not a diagnosis.
What's my BMI, and how do I read the number?
Your BMI is a single number that maps to a category: below 18.5 is underweight, 18.5-24.9 is the healthy weight range, 25.0-29.9 is overweight, and 30.0 or above falls into the obesity range. The number is a screening signal, not a verdict on your health, so use it as one input among many.