BMI Calculator
Calculate your Body Mass Index instantly. Find out if your weight is in a healthy range for your height.
How to Calculate BMI
Body Mass Index (BMI) is a simple measure that uses your height and weight to estimate whether you're underweight, at a healthy weight, overweight, or obese. It's widely used by healthcare professionals as a screening tool.
BMI Formula
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = weight (lbs) × 703 ÷ height (inches)²
Understanding BMI Categories
- Underweight: BMI < 18.5 — May indicate nutritional deficiency or other health issues
- Normal weight: BMI 18.5–24.9 — Generally associated with the lowest health risks
- Overweight: BMI 25–29.9 — Increased risk of heart disease, diabetes, and other conditions
- Obese Class I: BMI 30–34.9 — Moderate risk
- Obese Class II: BMI 35–39.9 — High risk
- Obese Class III: BMI ≥ 40 — Very high risk (severe obesity)
Limitations of BMI
While BMI is a useful screening tool, it has important limitations:
- Doesn't measure body fat directly — A muscular athlete may have a high BMI but low body fat
- Doesn't account for age or gender — Older adults tend to have more body fat at the same BMI
- Doesn't distinguish fat distribution — Abdominal fat is more dangerous than fat in the hips or thighs
- Not ideal for all ethnicities — Some populations have higher health risks at lower BMI levels
For a more complete picture, consider combining BMI with waist circumference measurement and body fat percentage testing.
Frequently Asked Questions
What is a healthy BMI range?
A healthy BMI is between 18.5 and 24.9. Below 18.5 is considered underweight, 25-29.9 is overweight, and 30 or above is classified as obese. These ranges are the same for adult men and women of all ages.
How is BMI calculated?
BMI is calculated by dividing your weight in kilograms by your height in meters squared: BMI = weight (kg) / height (m)². For imperial units: BMI = weight (lbs) × 703 / height (inches)². Our calculator handles both systems automatically.
Is BMI accurate for athletes?
BMI may overestimate body fat in athletes and muscular individuals because muscle is denser than fat. A muscular person may have a high BMI but low body fat percentage. For athletes, body fat percentage or waist-to-hip ratio may be better indicators.
What BMI is considered obese?
A BMI of 30 or above is classified as obese. Class I obesity is 30-34.9, Class II is 35-39.9, and Class III (severe obesity) is 40 or above. Obesity increases the risk of heart disease, type 2 diabetes, and certain cancers.
Does BMI apply to children?
For children and teens (ages 2-19), BMI is calculated the same way but interpreted using age- and sex-specific growth charts. A BMI at the 85th-94th percentile is considered overweight, and 95th percentile or above is obese. Pediatricians use CDC growth charts for assessment.
What is a good BMI for my age?
For adults, the healthy BMI range (18.5-24.9) is the same regardless of age. However, some research suggests a slightly higher BMI (25-27) may be protective in adults over 65. Always consult your healthcare provider for personalized advice based on your overall health.