BMI Calculator

How to Use the BMI Calculator

The BMI Calculator determines your Body Mass Index, a widely used screening tool that categorizes weight status based on height and weight. While BMI does not directly measure body fat, it provides a useful starting point for assessing whether your weight falls within a healthy range.

Entering Your Measurements

Select your preferred unit system (imperial or metric). For imperial, enter your height in feet and inches and weight in pounds. For metric, enter height in centimeters and weight in kilograms. Click Calculate to see your BMI value and category.

The BMI Formula

Metric: BMI = weight (kg) / height (m)². For a person who is 1.75 m tall and weighs 70 kg: BMI = 70 / (1.75)² = 70 / 3.0625 = 22.86.

Imperial: BMI = (weight (lbs) × 703) / height (inches)². For someone 5 feet 9 inches (69 inches) and 160 lbs: BMI = (160 × 703) / (69)² = 112,480 / 4,761 = 23.63.

BMI Categories

The World Health Organization defines these categories: Underweight is below 18.5, Normal weight is 18.5 to 24.9, Overweight is 25.0 to 29.9, Obesity Class I is 30.0 to 34.9, Obesity Class II is 35.0 to 39.9, and Obesity Class III is 40.0 and above. The calculator displays your category and how far you are from adjacent ranges.

Healthy Weight Range

Based on your height, the calculator shows the weight range that corresponds to a normal BMI (18.5-24.9). For someone 5 feet 8 inches tall, the healthy weight range is approximately 126 to 164 pounds. This gives you a concrete target range for weight management.

Limitations of BMI

BMI does not distinguish between muscle and fat. Athletes and bodybuilders may have high BMIs despite being lean and fit. BMI also does not account for age, sex, ethnicity, or body composition. It is a screening tool, not a diagnostic measure. Consult a healthcare provider for a complete health assessment.

Frequently Asked Questions

Q: Is BMI accurate for athletes?

A: BMI may overestimate body fat in muscular individuals. A muscular person at 5 feet 10 inches and 200 lbs has a BMI of 28.7 (overweight), yet may have low body fat. For athletes, body fat percentage measurements like skinfold calipers or DEXA scans are more accurate.

Q: Does BMI differ for children?

A: Yes. For children and teens (ages 2-19), BMI is age and sex-specific, expressed as a percentile. A child at the 85th percentile is considered overweight. This calculator is designed for adults aged 20 and older.

Q: What BMI should I aim for?

A: A BMI between 18.5 and 24.9 is considered normal. Many health professionals suggest aiming for the middle of this range (around 21-23) for optimal health outcomes. However, individual factors like muscle mass, bone density, and overall fitness level matter more than a single number.