BMI Calculator
Enter your height and weight below to get your body mass index and see exactly which WHO category you fall into. The calculator works in both metric and imperial units.
| Underweight | Below 18.5 |
| Normal weight | 18.5 to 24.9 |
| Overweight | 25.0 to 29.9 |
| Obese | 30.0 and above |
How to Use This BMI Calculator
Choose your preferred unit system at the top. Enter your current weight and height then hit Calculate. Your BMI and category appear instantly on the right.
The healthy weight range shown beneath your number tells you exactly what weight you would need to be at your current height to sit in the 18.5 to 24.9 zone. This gives you a concrete target rather than just a category label.
Use this alongside the Calorie Calculator and TDEE Calculator for a complete picture of your health metrics. BMI is a useful screening number but it works best when combined with other data points.
The BMI Formula
BMI stands for body mass index. The formula divides weight by the square of height:
Metric: BMI = weight (kg) / height (m)²
Imperial: BMI = (weight (lb) / height (in)²) x 703
The number was created by Belgian mathematician Adolphe Quetelet in the 1830s. It became a medical screening tool in the 1970s when Ancel Keys validated it against body fat measurements. The World Health Organization adopted the current category thresholds in 1995.
The formula does not account for where fat is distributed on the body. Waist circumference is often a better predictor of metabolic disease because abdominal fat is more metabolically active than fat stored around the hips and thighs.
BMI Calculation Examples
- Person A: 70 kg, 175 cm. BMI = 70 / (1.75 x 1.75) = 22.9. Normal weight. Healthy weight range at this height: 56.7 to 76.3 kg.
- Person B: 90 kg, 180 cm. BMI = 90 / (1.80 x 1.80) = 27.8. Overweight. To reach the top of the healthy range this person would need to weigh around 80.6 kg.
- Person C: 155 lb, 5 ft 6 in (168 cm). BMI = (155 / (66 x 66)) x 703 = 25.0. Right on the border of normal and overweight. This illustrates why a single pound up or down can shift your category.
Frequently Asked Questions
What is a healthy BMI range?
The World Health Organization defines healthy adult BMI as 18.5 to 24.9. Below 18.5 is underweight. Between 25 and 29.9 is overweight. A BMI of 30 or above falls into the obese category. These are broad population-level benchmarks and individual health depends on many more factors than this single number.
Is BMI the same for men and women?
The formula is identical. However women naturally carry a higher percentage of body fat at the same BMI than men because of biological differences in body composition. A woman with a BMI of 22 and a man with a BMI of 22 will typically have quite different body fat percentages. This is normal and expected, not a flaw in the formula.
Can I have a normal BMI but still be unhealthy?
Absolutely. A very muscular athlete can have a BMI of 27 with extremely low body fat and excellent cardiovascular health. Someone who is sedentary could have a BMI of 23 while carrying dangerous levels of visceral fat. BMI is a population-level screening tool. It is not designed to diagnose individual health status on its own.
How do I calculate BMI in kg and cm?
Convert your height to metres first. Then divide your weight in kilograms by your height in metres squared. A person who is 70 kg and 175 cm tall: 1.75 x 1.75 = 3.0625, then 70 / 3.0625 = 22.9. This calculator does that calculation for you the moment you enter your numbers.
Does BMI change with age?
The standard formula does not adjust for age in adults. In practice, body composition shifts significantly between your 20s and your 60s. Muscle mass decreases and body fat increases even when your weight stays the same. Some researchers suggest adjusting thresholds upward for adults over 65, but the WHO ranges remain the standard reference point in clinical settings worldwide.
Guides for the BMI Calculator
Longer reads on the maths and the practical side of this tool.