BMI calculator

Your Body Mass Index (BMI) is one of the simplest ways to understand whether your weight is in a healthy range for your height. RNfinity's free BMI Calculator helps you instantly check your body mass index, giving you a clear idea of whether you're underweight, a healthy weight, overweight, or in the obese range. Using your height and weight, this body mass index calculator provides a science-based estimate that can guide your nutrition and fitness decisions.

Our BMI calculator is suitable for both men and women, using the same proven formula trusted by health professionals and even featured on the NHS BMI checker. Whether you're just starting your fitness journey, looking to manage your weight, or tracking your progress toward a goal, this simple body weight index calculator gives you fast, accurate insights into your current health status.

BMI, short for Body Mass Index, is calculated by dividing your weight in kilograms by your height in meters squared (kg/m²). This figure estimates body fat levels relative to height and weight. While it doesn't directly measure fat, it's one of the most widely used indicators of general health.

Our online BMI calculator handles the math instantly — you just enter your height and weight, and it returns your BMI score along with your classification based on official BMI charts for men and women.

The general BMI ranges are:

You can also explore our BMI chart for women or BMI index chart for men for visual guidance and comparison.

Knowing your BMI helps you make informed lifestyle choices. If your BMI score is higher than recommended, it might be a sign to adjust your diet, increase physical activity, or consult a healthcare professional. Conversely, a low BMI could suggest you're not eating enough or may need to gain weight for better health.

Our tool also doubles as a body mass calculator and body weight index calculator, helping you monitor progress over time and set realistic goals.

While BMI is a useful indicator, it's important to remember it's not a perfect measure of body composition. Muscle mass, bone density, and age can all influence results. That's why RNfinity links this BMI calculator with other tools — such as our calorie calculator, protein calculator, and TDEE calculator — giving you a complete picture of your body's nutritional and energy needs.