BMI Calculator

BMI Calculator: Understanding Your Body Mass Index

A BMI (Body Mass Index) calculator is a simple tool that helps assess whether your weight is in a healthy range for your height. While not a direct measure of body fat, BMI correlates with more direct measures of body fat and offers a quick screening method for weight categories.

How BMI is Calculated

The BMI formula is simple and uses your weight and height measurements:

BMI = weight (kg) / (height (m) × height (m))

Or for those using imperial measurements:

BMI = (weight (lb) / (height (in) × height (in))) × 703

BMI Categories for Adults

BMI Range	Category	Health Risk
Below 18.5	Underweight	Possible nutritional deficiency and osteoporosis
18.5 – 24.9	Normal weight	Low risk (healthy range)
25.0 – 29.9	Overweight	Moderate risk of developing heart disease, high blood pressure, diabetes
30.0 – 34.9	Obese class I	High risk
35.0 – 39.9	Obese class II	Very high risk
40.0 and above	Obese class III	Extremely high risk

Why Knowing Your BMI Matters

• Health screening: Identifies potential weight problems
• Disease risk: Higher BMI correlates with increased risk for many conditions
• Treatment planning: Helps healthcare providers make recommendations
• Progress tracking: Useful for monitoring weight changes over time
• Population health: Public health officials use BMI data to track trends

Limitations of BMI

While BMI is a useful screening tool, it has limitations:

• Muscle mass: May overestimate body fat in athletes
• Age differences: May underestimate body fat in older adults
• Ethnic variations: Some ethnic groups have different risk thresholds
• Body composition: Doesn’t distinguish between fat and muscle
• Fat distribution: Doesn’t account for where fat is stored (visceral vs subcutaneous)

Alternative Measurements

Measurement	What It Assesses	Advantages
Waist circumference	Abdominal fat	Better predictor of visceral fat and metabolic risk
Waist-to-hip ratio	Body fat distribution	Accounts for different body shapes
Body fat percentage	Actual fat mass	Direct measure of body composition
Skinfold thickness	Subcutaneous fat	Estimates body fat percentage

BMI for Different Populations

Children and Teens

BMI is calculated differently for those under 20, using percentiles that compare to children of the same age and sex.

Older Adults

BMI ranges may need adjustment as body composition changes with age.

Athletes

Those with high muscle mass may have high BMI without excess fat.

Pregnant Women

BMI calculations aren’t useful during pregnancy as weight gain is expected.

Health Risks Associated with High BMI

• High blood pressure
• Type 2 diabetes
• Coronary heart disease
• Stroke
• Gallbladder disease
• Osteoarthritis
• Sleep apnea
• Certain cancers
• Lower quality of life
• Mental illness such as depression

Health Risks Associated with Low BMI

• Malnutrition
• Vitamin deficiencies
• Anemia
• Osteoporosis
• Decreased immune function
• Growth and development issues (in children)
• Reproductive problems

When to See a Doctor

Consult a healthcare provider if:

• Your BMI is 30 or higher
• Your BMI is below 18.5
• You’ve experienced rapid weight changes
• You have other health concerns along with weight changes
• You want personalized advice about your weight

Use our BMI calculator as a starting point for understanding your weight status, but remember it’s just one indicator of health. A comprehensive assessment from a healthcare professional provides the most accurate picture of your health status.