Calculate Your Body Mass Index

What Is a BMI Calculator?

A BMI calculator (Body Mass Index calculator) is a free health screening tool that estimates your body fat level from your height and weight. BMI is calculated by dividing weight in kilograms by the square of height in metres (kg/m²). Our advanced BMI calculator supports both metric (kg, cm) and imperial (lbs, ft/in) inputs, displays your WHO health category on a colour-coded visual scale, shows your healthy weight range for your exact height, calculates how much weight you would need to lose or gain to reach the normal range, and — when you optionally provide your age and gender — estimates your body fat percentage using the peer-reviewed Deurenberg (1991) formula.

BMI is the most widely used initial screening tool for weight-related health risks by doctors, nurses and public health authorities worldwide. A BMI between 18.5 and 24.9 is associated with the lowest risk of weight-related chronic diseases including type 2 diabetes, hypertension and cardiovascular disease. While BMI has limitations (it does not directly measure body fat and cannot distinguish muscle from fat), it remains a quick, free and clinically recognised starting point for understanding your weight status before consulting a healthcare professional.

How to Use the BMI Calculator - Step by Step

1. 1

   Choose your unit system

   Select Metric (kg / cm) or Imperial (lbs / ft + in) using the toggle at the top of the form. The input fields change automatically to match your selection.

2. 2

   Enter your weight

   Type your current body weight in kilograms (metric) or pounds (imperial). Use your most recent measurement for the most accurate result.

3. 3

   Enter your height

   Enter your height in centimetres (metric) or in feet and inches (imperial). Your height directly determines your healthy weight range.

4. 4

   Add age and gender (optional)

   Providing your age in years and biological gender unlocks a body fat percentage estimate using the Deurenberg formula — a widely cited clinical tool.

5. 5

   Click 'Calculate BMI'

   Get your BMI score, WHO category, visual BMI scale position, healthy weight range, weight to lose or gain, and — if age and gender were entered — a body fat percentage estimate.

Frequently Asked Questions - BMI Calculator

What is a healthy BMI range for adults?

According to the World Health Organization (WHO), a BMI between 18.5 and 24.9 is classified as Normal weight and is associated with the lowest health risk for most adults. BMI below 18.5 is Underweight; 25–29.9 is Overweight; 30 and above is Obese (split into Class I, II and III).

Is BMI accurate for athletes and bodybuilders?

BMI can overestimate body fat in very muscular individuals such as athletes, as it does not distinguish between muscle mass and fat mass. A sports physician, skinfold measurement or DEXA scan provides a more accurate body composition assessment for athletes.

Does BMI use the same thresholds for men and women?

The standard BMI formula and WHO cut-off thresholds are the same for both sexes. However, women typically carry a higher percentage of body fat at the same BMI compared to men, which is why sex is factored into the optional Deurenberg body fat estimate.

What is the Deurenberg body fat percentage formula?

Published in 1991, the Deurenberg formula estimates body fat % as: (1.2 × BMI) + (0.23 × Age) − (10.8 × Sex) − 5.4, where Sex = 0 for males and 1 for females. It is a population-level approximation widely cited in clinical literature and is most accurate for adults of average body composition.

Should I consult a doctor based on my BMI result?

If your BMI falls outside the 18.5–24.9 normal range, a conversation with your GP or healthcare provider is worthwhile. They can consider your full medical history, ethnicity (BMI cut-offs differ for some Asian populations) and lifestyle before giving personalised advice. Our tool is a screening aid, not a medical diagnosis.

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