⚖️ BMI Calculator
Enter your height and weight to calculate your Body Mass Index.
What is this tool?
Body Mass Index (BMI) is a widely used numerical screening tool that estimates whether a person's body weight is appropriate for their height. Developed in the 1830s by the Belgian mathematician and astronomer Adolphe Quetelet, BMI was originally known as the Quetelet Index before being popularized under its current name by physiologist Ancel Keys in 1972. Today, the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), and countless healthcare providers rely on BMI as a quick, inexpensive population-level indicator of underweight, healthy weight, overweight, and obesity. Because the calculation requires only height and weight, BMI is easy to measure in nearly any setting, from a doctor's office to a fitness app. While BMI does not directly measure body fat, it correlates strongly with more accurate methods such as underwater weighing and dual-energy X-ray absorptiometry (DEXA) for most adults. It is most useful for tracking trends over time and for identifying people who may benefit from further assessment, lifestyle changes, or medical evaluation.How it works
The BMI formula divides body weight in kilograms by the square of height in meters: BMI = weight (kg) / height² (m²). For imperial units, the equivalent formula is BMI = 703 × weight (lb) / height² (in²). For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 / (1.75 × 1.75) = 22.9, which falls in the normal range. Because the calculation squares height, taller and shorter individuals are scaled appropriately.How to use
- Select your preferred measurement system — metric (kilograms and centimeters) or imperial (pounds and feet/inches).
- Enter your height in the corresponding field.
- Enter your current body weight.
- Optionally, enter your age and select your biological sex, which can add context for interpretation.
- Click the Calculate button. The tool instantly displays your BMI value, the category it falls into, and your healthy weight range for your height. Use the reference table below to understand where your result sits and what actions, if any, you might discuss with a healthcare professional.
Reference Table
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese (Class I) |
| 35.0 – 39.9 | Obese (Class II) |
| 40.0 and above | Obese (Class III) |
Frequently Asked Questions
Is BMI accurate for everyone?
No single number can capture the full picture of health. BMI is a reliable screening tool for most adults, but it does not distinguish between fat mass and muscle mass. It also tends to overestimate body fat in some populations and underestimate it in others, so it should be interpreted alongside waist circumference, activity level, and overall health markers.
Does BMI work for athletes and people with high muscle mass?
For athletes and very muscular individuals, BMI frequently classifies them as overweight or obese even when their body fat percentage is low. This happens because muscle is denser than fat. In these cases, body fat percentage or waist-to-hip ratio may offer a clearer view of metabolic health.
Is BMI suitable for children and teens?
Children and adolescents are assessed using BMI-for-age percentile charts rather than fixed adult thresholds, because body composition changes with growth. A pediatrician should interpret results for anyone under 20, not the standard adult categories shown here.
Should pregnant women use BMI?
BMI is still relevant before pregnancy, but weight gain recommendations during pregnancy depend on pre-pregnancy BMI. Pregnant women should always consult a healthcare provider for personalized guidance rather than relying on standard adult BMI categories.