BMI Calculator

Calculate your Body Mass Index instantly. See your BMI category, healthy weight range for your height, and a visual gauge — using WHO standards. Supports both Imperial and Metric units.

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Understanding BMI: A Complete Guide

Body Mass Index (BMI) is one of the most widely used health screening tools in the world. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, it provides a quick estimate of body fat based on height and weight. Here's everything you need to know about BMI and how to use it wisely.

How BMI Is Calculated

The BMI formula is straightforward: divide your weight in kilograms by your height in meters squared (BMI = kg / m²). For Imperial units: BMI = (weight in lbs × 703) / (height in inches)². The result is a single number that falls into one of several categories defined by the World Health Organization.

What Your BMI Means

A BMI under 18.5 suggests underweight, which can indicate malnutrition or other health concerns. The 18.5–24.9 range is considered normal weight and is associated with the lowest health risks. BMI 25–29.9 falls in the overweight category, and 30+ indicates obesity with progressively higher health risks.

Limitations of BMI

Beyond BMI: Other Health Metrics

Use this BMI calculator as a starting point, then track practical next steps. Estimate your daily intake with our calorie calculator, plan training targets with the pace calculator, and split macros with the percentage calculator. If you are building a long-term routine, our age calculator can also help when setting age-based health milestones.

Frequently Asked Questions

What is BMI and how is it calculated?
BMI (Body Mass Index) is calculated by dividing your weight in kilograms by your height in meters squared: BMI = kg / m². It's a simple screening tool used worldwide to categorize weight status. For Imperial units, the formula is BMI = (weight in lbs × 703) / (height in inches)².
What are the WHO BMI categories?
The World Health Organization defines four main categories: Underweight (BMI below 18.5), Normal weight (18.5–24.9), Overweight (25.0–29.9), and Obese (30.0 and above). Obesity is further divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+).
Is BMI accurate for everyone?
BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat mass, so athletes may show as "overweight" despite being healthy. It also doesn't account for age, gender, ethnicity, or body fat distribution. Always consult a healthcare provider for a complete assessment.
What is a healthy BMI range?
A BMI between 18.5 and 24.9 is considered normal/healthy weight by the WHO. However, optimal BMI can vary by age, gender, and ethnicity. Some research suggests a BMI of 20–25 is associated with the lowest health risks for most adults.
How does BMI differ for children and teens?
For children and teens (ages 2–19), BMI is calculated the same way but interpreted using age- and sex-specific percentile charts from the CDC. A child's BMI percentile shows how their BMI compares to other children of the same age and sex. This calculator is designed for adults (18+).
Can BMI predict health risks?
Higher BMI is statistically associated with increased risk of heart disease, type 2 diabetes, high blood pressure, certain cancers, and other conditions. However, BMI alone isn't diagnostic — factors like fitness level, waist circumference, diet, and family history also matter significantly.
Should I use BMI or body fat percentage?
Both are useful. BMI is quick and easy to calculate without special equipment. Body fat percentage (measured via DEXA scan, calipers, or smart scales) gives a more detailed picture of body composition. For most people, BMI is a reasonable first screening tool, with body fat percentage providing additional insight.

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