📌 BMI is a screening tool, not a diagnostic measure. Consult a healthcare professional for a full assessment.

About the BMI Calculator

Body Mass Index, or BMI, is the most widely used screening tool in medicine for categorizing weight relative to height. In seconds, it provides a number that helps healthcare providers identify whether a patient may be at risk for weight-related health conditions such as type 2 diabetes, heart disease, high blood pressure, and sleep apnea.

Our BMI Calculator supports both metric (kilograms and centimeters) and imperial (pounds and inches) inputs. Enter your height and weight, and you'll instantly see your BMI value alongside the World Health Organization's standard weight categories.

How It Works

BMI divides your weight (in kilograms) by the square of your height (in meters). For imperial measurements, a conversion factor of 703 is applied to keep the equation consistent. The result is a dimensionless number that falls into one of five standard WHO categories.

Formula / Key Reference

Metric: BMI = weight (kg) ÷ height² (m²)
Imperial: BMI = 703 × weight (lbs) ÷ height² (in²)

WHO Categories:

< 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 = Obese (Class III / Severe)

Real-World Example

Person: Female, 165 cm tall (5'5"), weighing 68 kg (150 lbs)

BMI = 68 ÷ (1.65)² = 68 ÷ 2.7225 ≈ 24.98

Category: Normal weight (just below the 25.0 Overweight threshold)

This result tells her she is within a healthy range, but it does not account for body composition. If she has been strength training, her muscle mass may push her BMI toward the higher end of normal even though her body fat percentage is low — illustrating both the utility and the limitation of BMI as a single screening metric.

Common Uses

  • Initial health screening at doctor's appointments
  • Setting a weight loss or gain target with a specific BMI goal in mind
  • Tracking BMI changes over time as part of a fitness program
  • Determining eligibility for certain medical procedures
  • Educational purposes in health and wellness courses

Frequently Asked Questions

Is BMI accurate for everyone? ▼
BMI is a useful screening tool but has known limitations. It overestimates body fat in athletes and people with high muscle mass, and underestimates it in older adults who have lost muscle. For a more complete picture, consider waist circumference, body fat percentage (via DEXA scan or bioelectrical impedance), and metabolic blood markers.
What is a healthy BMI for adults? ▼
For adults 20 and older, a BMI between 18.5 and 24.9 is considered normal by the WHO. However, optimal BMI can vary by age and ethnicity. Some Asian health organizations, for example, use lower cutoffs due to higher metabolic risk at lower BMIs in Asian populations.
How do I lower my BMI? ▼
Lower BMI is achieved by reducing body fat through a combination of a moderate caloric deficit, regular aerobic and resistance exercise, quality sleep, and managing stress hormones. Sustainable fat loss of 0.5–1 lb per week is generally recommended over rapid dieting.
Does BMI apply to children? ▼
Children and teenagers use age- and sex-specific BMI percentile charts rather than the fixed adult categories, because healthy body composition changes significantly with growth. A pediatrician interprets BMI-for-age percentile rather than the raw number.