BMI Calculator
Enter your height and weight to calculate your (Body Mass Index). BMI is a simple number that tells you whether your weight is in a healthy range for your height. It is not perfect, but it is a useful starting point.
This calculator provides estimates for educational purposes only. It is not medical advice. Always consult a healthcare professional before making changes to your diet or exercise routine.
What Is BMI?
is a simple screening tool that estimates whether your weight falls within a healthy range relative to your height. It was developed in the early 19th century by mathematician Adolphe Quetelet and remains one of the most widely used metrics in clinical settings, public health research, and personal fitness tracking.
BMI does not directly measure body fat, muscle, or bone density. Instead, it provides a quick numerical snapshot that can flag potential weight-related health risks. Because it only requires two inputs — weight and height — it is easy to calculate at home without any special equipment.
Despite its simplicity, BMI is a useful starting point for understanding your overall body composition. It is most informative when combined with other measurements such as , waist circumference, and blood work.
How Is BMI Calculated?
The formula is straightforward. In metric units:
BMI = weight (kg) / height (m)²
For example, a person who weighs 70 kg and stands 1.75 m tall has a BMI of 70 / (1.75 × 1.75) = 22.9. In imperial units the formula is adjusted with a conversion factor: weight (lbs) / height (in)² × 703.
What Do the Results Mean?
The World Health Organization classifies BMI into the following categories for adults:
- Underweight: below 18.5
- Normal weight: 18.5 – 24.9
- Overweight: 25.0 – 29.9
- Obese Class I: 30.0 – 34.9
- Obese Class II: 35.0 – 39.9
- Obese Class III: 40.0 and above
A BMI in the normal range generally correlates with lower risk of cardiovascular disease, type 2 diabetes, and certain cancers. However, these thresholds are population-level guidelines, not individual diagnoses.
Limitations of BMI
BMI cannot distinguish between muscle mass and fat mass. A muscular athlete may register as overweight or even obese despite having a low body fat percentage. Similarly, an older adult with little muscle mass could have a normal BMI yet carry excess body fat — a condition sometimes called "normal weight obesity."
Age, sex, and ethnicity also affect how BMI relates to health outcomes. Research shows that certain populations experience elevated metabolic risk at lower BMI thresholds. For these reasons, many health professionals recommend pairing BMI with a measurement for a more complete picture.
Tips for Using BMI Effectively
- Treat BMI as a screening tool, not a diagnosis. A single number cannot capture your full health profile.
- Track BMI over time rather than fixating on a single reading. Trends matter more than any individual measurement.
- If your BMI suggests a potential concern, follow up with additional assessments such as waist circumference, body fat testing, or a consultation with a healthcare provider.
- Pair BMI with strength and cardiovascular fitness markers for a well-rounded view of your health.
Related Calculators
For a deeper look at your body composition, try the Body Fat Calculator to estimate your fat-to-lean ratio, or use the Ideal Body Weight Calculator to see how different clinical formulas define a healthy weight for your height and frame.
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