BMI Calculator

A BMI Calculator turns your weight and height into a single number that helps you gauge whether your weight sits in a healthy range for your height.

This tool works in both metric (kilograms and centimetres) and imperial (pounds, feet, and inches) units, updates the moment you type, and runs entirely in your browser so nothing you enter is sent anywhere.

What BMI actually measures

Body Mass Index is a ratio of weight to height, not a direct measure of body fat.

It was designed as a quick population-level screening figure, so it treats everyone the same regardless of how much of their weight is muscle, bone, or fat.

That makes it a useful starting point, but a very athletic person can read as overweight while carrying little fat.

Reading your category

The standard adult bands are Underweight below 18.5, Normal from 18.5 to 24.9, Overweight from 25 to 29.9, and Obese at 30 and above.

The calculator also shows the healthy weight range for your exact height — the span of weights that would place your BMI between 18.5 and 24.9.

If you like turning figures into proportions, you can express a target loss or gain as a share of your current weight with a Percentage Calculator.

Switching between metric and imperial

Toggle the unit system and the fields relabel automatically, so you never have to convert by hand.

Under the hood the metric formula is weight in kilograms divided by height in metres squared, while the imperial version multiplies by 703 to work in pounds and inches.

When you need to line up a measurement that came from a different system, a Unit Converter keeps your inputs consistent, and tracking BMI on birthdays is easy with an Age Calculator.

Frequently Asked Questions

How is BMI calculated?

In metric units BMI is your weight in kilograms divided by the square of your height in metres. In imperial units it is 703 times your weight in pounds divided by the square of your height in inches. Both formulas give the same BMI number.

What is a healthy BMI range?

For most adults a BMI between 18.5 and 24.9 is considered the normal, healthy range. Below 18.5 is classed as underweight, 25 to 29.9 as overweight, and 30 or above as obese.

Is BMI accurate for everyone?

No. BMI does not separate muscle from fat and ignores age, sex, and body composition, so athletes and older adults can be misclassified. Treat it as a rough screening figure and speak to a healthcare professional for a fuller picture.

Is my data kept private?

Yes. Every calculation happens locally in your browser with JavaScript. Nothing you type is uploaded, logged, or stored, and the tool keeps working offline once the page has loaded.