BMI Calculator
Enter your height and weight to see your Body Mass Index and where it falls on the standard reference scale — instantly.
This calculator is for general information and tracking only, and is not a medical diagnosis. BMI is a population-level screening number — it doesn't account for muscle mass, bone density or fat distribution. If you have questions about your health, talk to a qualified healthcare professional.
How it works
Choose your units
Switch between metric (cm, kg) and imperial (ft/in, lb) — whichever you have on hand.
Enter height and weight
Type the values or use the sliders. The result updates as you go.
See your BMI and range
Your BMI number and standard category appear instantly, with a scale showing where it falls.
What people use a BMI calculator for
A quick BMI check is a common first step in a few everyday situations.
Before a doctor's visit
Tracking a training plan
Comparing over time
Filling out forms
General awareness
A few things worth knowing about BMI
Body Mass Index is a simple ratio of weight to height, and its main job is to act as a fast, free checkpoint — a number you can get in seconds without any special equipment, and compare against standard reference ranges that are used the same way across most of the world. That's exactly why it's so widely used: not because it's a complete picture, but because it's an easy starting point.
The main thing to keep in mind is what BMI can't see. It's calculated from height and weight alone, so it can't tell the difference between muscle and fat, doesn't factor in bone density, and says nothing about where on the body weight is carried — all of which affect how much a single BMI number actually reflects about any one person. On its own, BMI isn't a diagnosis; it's one data point among several a health professional would look at.
If you're tracking your BMI over time, try to measure under similar conditions each time — roughly the same time of day, similar clothing, and a consistent scale — since small measurement differences can shift the number enough to make a trend look noisier than it really is. It's also worth double-checking your units before trusting a surprising result: mixing up centimeters with inches, or kilograms with pounds, is the single most common reason a BMI calculation comes out looking wrong.
Frequently asked questions
How is BMI calculated?
BMI is your weight in kilograms divided by the square of your height in meters. If you enter imperial units (feet/inches and pounds), the calculator converts them to metric first and applies the same formula.
What do the BMI categories mean?
They're standard reference ranges used to describe where a BMI value falls: underweight, healthy weight, overweight, and obesity. They're population-level reference points, not a judgment or a diagnosis for any individual.
Is BMI an accurate measure of health?
BMI is a quick screening number, not a full health assessment. It doesn't distinguish muscle mass from fat, doesn't account for bone density, and doesn't show where fat is distributed on the body — all things that affect how meaningful a given BMI number is for a specific person.
Why does my BMI look different when I switch units?
It shouldn't, as long as the same height and weight are entered — the calculator converts imperial to metric before computing. If a result looks off, double-check you didn't mix feet with centimeters or kilograms with pounds, since a unit mix-up is the most common cause of a confusing BMI number.
Is this BMI calculator free to use?
Yes, completely free, with no account or sign-up, and it runs entirely in your browser.
Should I use this instead of seeing a doctor?
No. This tool is for general information and tracking only, not a medical diagnosis. Talk to a healthcare professional about what your numbers mean for your specific situation.