This tool is for informational purposes only and does not constitute medical advice. Always consult a healthcare professional.
How the BMI Calculator Works
Body Mass Index (BMI) is a simple numerical value derived from your weight and height. It is widely used by healthcare professionals, fitness experts, and individuals as a quick screening tool to categorise weight status. The formula divides your weight in kilograms by the square of your height in metres (kg/m²). While BMI does not directly measure body fat, it correlates with more direct measures and is useful for identifying potential weight-related health risks at the population level.
This calculator supports both metric and imperial units. If you enter your height in feet and inches or your weight in stones and pounds, the tool automatically converts these values to metric before applying the formula. The result is colour-coded to clearly indicate which BMI category you fall into: underweight, healthy weight, overweight, or obese. The tool also displays the healthy weight range for your specific height so you can see where you stand relative to the recommended range.
How to Use This Tool
- Choose your height unit — select centimetres or feet and inches from the dropdown, then enter your height.
- Choose your weight unit — select kilograms or stones and pounds, then enter your weight.
- Click Calculate BMI — your BMI value and category appear instantly, along with the healthy weight range for your height.
- Review your result — the colour-coded category makes it easy to see where you fall on the BMI scale.
- Copy the result — click "Copy Result" to copy the BMI value and category to your clipboard.
How It Works Behind the Scenes
The BMI calculation uses the standard formula: BMI = weight (kg) / height (m)². When imperial units are selected, the tool first converts feet and inches to centimetres (1 foot = 30.48 cm, 1 inch = 2.54 cm) and stones and pounds to kilograms (1 stone = 6.35029 kg, 1 pound = 0.453592 kg). The height in centimetres is then converted to metres by dividing by 100. The BMI value is rounded to one decimal place for clarity.
The healthy weight range is calculated by rearranging the BMI formula. For a BMI of 18.5, the minimum healthy weight equals 18.5 multiplied by height in metres squared. For a BMI of 24.9, the maximum healthy weight equals 24.9 multiplied by height in metres squared. These values are displayed in the unit system you selected, giving you a clear target range to aim for.
Frequently Asked Questions
What is BMI and how is it calculated?
BMI stands for Body Mass Index. It is calculated by dividing your weight in kilograms by your height in metres squared (kg/m²). For example, a person weighing 70 kg who is 1.75 m tall would have a BMI of 70 / (1.75 x 1.75) = 22.9. It is a widely used screening tool for categorising weight status and identifying potential health risks related to weight.
What are the BMI categories?
The standard BMI categories defined by the World Health Organisation are: Underweight (below 18.5), Healthy weight (18.5 to 24.9), Overweight (25 to 29.9), and Obese (30 and above). These categories apply to adults and are used globally as a general guide. Some health organisations further subdivide the obese category into Class I (30-34.9), Class II (35-39.9), and Class III (40+).
Is BMI accurate for everyone?
BMI is a useful screening tool for the general population, but it has important limitations. It does not distinguish between muscle mass and fat mass, so athletes or very muscular individuals may have a high BMI without having excess body fat. It also does not account for age, gender, ethnicity, or where fat is distributed on the body. For a complete health assessment, consult a healthcare professional who can consider additional factors.
Can I use imperial units with this calculator?
Yes. This calculator supports both metric (centimetres and kilograms) and imperial (feet/inches and stones/pounds) units. Simply use the dropdown menus to switch between unit systems. The calculator automatically converts your inputs internally and computes the BMI using the standard metric formula, so the result is accurate regardless of which units you prefer.
What is a healthy BMI range?
A healthy BMI is generally considered to be between 18.5 and 24.9 for adults. This range is associated with the lowest statistical risk of weight-related health problems such as heart disease, type 2 diabetes, high blood pressure, and certain cancers. However, BMI is only one indicator of health and should be considered alongside other metrics such as waist circumference, blood pressure, and cholesterol levels.
Is my data stored when I use this BMI calculator?
No. All calculations are performed entirely in your browser using JavaScript. Your height, weight, and BMI result are never transmitted to any server, stored in any database, or logged in any analytics system. Once you close or refresh the page, all entered data is gone. Daytics is committed to protecting your privacy and has designed all its tools to operate completely client-side.
