About the BMI Calculator
A free, instant body mass index calculator with metric and imperial input, WHO weight category, and healthy weight range for your height.
What it is
The BMI Calculator computes your body mass index the moment you enter your height and weight — no button to click, no page to reload. It accepts both metric (centimetres and kilograms) and imperial (feet, inches, and pounds) values and converts between them automatically, so you always get the same result regardless of which unit system you prefer.
Alongside the BMI number itself, the tool shows the standard World Health Organization weight category your result falls into and the weight range generally considered healthy for your specific height. Everything runs in your browser — your height and weight are never sent to a server or stored anywhere.
Key features
Metric & imperial input
Switch between metric (cm, kg) and imperial (ft/in, lb) at any time. The result updates instantly in either mode, and the healthy weight range is shown in whichever unit you've selected.
BMI value & WHO category
Your BMI is displayed to one decimal place alongside the WHO weight category — underweight, healthy weight, overweight, or obese — with a colour-coded badge so the category is immediately clear.
Healthy weight range for your height
The tool calculates the minimum (BMI 18.5) and maximum (BMI 25) weight that falls in the healthy range for your specific height, shown in your chosen unit alongside your result.
Visual BMI scale
A colour-banded scale bar positions your result across the four WHO ranges — underweight, healthy, overweight, and obese — so you can see at a glance where you sit relative to each boundary.
How BMI is calculated
Metric formula
BMI = weight (kg) ÷ height (m)². Height in centimetres is divided by 100 to convert to metres before squaring.
Imperial formula
BMI = 703 × weight (lb) ÷ height (in)². Feet and inches are combined into total inches. The two formulas produce identical results.
WHO boundaries
Underweight: below 18.5. Healthy weight: 18.5–24.9. Overweight: 25–29.9. Obese: 30 and above.
Healthy weight range
Minimum = 18.5 × height (m)². Maximum = 25 × height (m)². These are the weights at which BMI hits 18.5 and 25 for your specific height.
A note on BMI's limitations
This tool is a general reference and is not medical or dietary advice. Please consult a registered dietitian or physician before making any significant change to your diet, nutrition, or weight. Individual needs vary, and only a qualified professional can give advice tailored to you.