BMI Calculator
Calculate your Body Mass Index instantly. Enter your height and weight to see your BMI value, weight category, and healthy weight range. Supports metric and imperial units.
BMI Calculator — Calculate Body Mass Index Online Free: Free BMI Calculator tool: calculate your BMI (Body Mass Index) instantly. Enter height and weight in metric or imperial units. See your BMI category.
How to Calculate BMI
Choose Units
Select Metric (cm/kg) or Imperial (ft-in/lbs). Enter your height and weight in the appropriate fields.
Calculate
Click "Calculate BMI" to see your Body Mass Index value, color-coded category, and position on the BMI scale.
Interpret
View your BMI category (Underweight, Normal, Overweight, or Obese) and the healthy weight range for your height.
What Is BMI?
Body Mass Index (BMI) is a numerical value calculated from a person's weight and height. The formula is simple: weight in kilograms divided by height in meters squared (BMI = kg/m²). For imperial units, the formula is (weight in pounds × 703) / (height in inches)². The result is a single number that categorizes individuals into weight groups: underweight (below 18.5), normal weight (18.5–24.9), overweight (25–29.9), and obese (30 and above).
BMI was invented by Belgian mathematician Adolphe Quetelet in the 1830s as part of his work on "social physics" — applying statistical methods to human populations. It was never intended as an individual health diagnostic tool but as a population-level statistic. The medical community adopted it in the 20th century because it's easy to calculate and correlates reasonably well with body fat percentage at the population level.
The World Health Organization (WHO) and most national health organizations use BMI as a primary screening tool for weight-related health risks. Research consistently shows that BMIs in the obese range (30+) are associated with higher rates of type 2 diabetes, cardiovascular disease, certain cancers, and reduced life expectancy. However, BMI has well-documented limitations: it doesn't distinguish between muscle and fat mass, account for fat distribution, or consider age, sex, or ethnicity.
Athletes and highly muscular individuals often have BMIs in the "overweight" range despite being in excellent physical condition because muscle is denser than fat. Conversely, sedentary older adults may have a "normal" BMI despite having high body fat percentage (sometimes called "skinny fat"). BMI is best used as one data point among many — not as a definitive health assessment. Waist circumference, body fat percentage, blood pressure, and blood lipid levels provide a more complete health picture.
BMI Categories
Underweight (<18.5)
May indicate insufficient nutrition, eating disorders, or underlying health conditions. Associated with weakened immunity and bone density loss. Consult a healthcare provider.
Normal (18.5–24.9)
Associated with the lowest risk of weight-related health problems. Maintaining a BMI in this range through balanced nutrition and regular exercise is generally recommended.
Overweight (25–29.9)
Elevated risk for cardiovascular disease, type 2 diabetes, and joint problems. Lifestyle modifications (diet and exercise) are typically recommended to reduce health risks.
Obese (30+)
Significantly increased risk for serious health conditions. Medical guidance is recommended. Sub-categories: Class I (30–34.9), Class II (35–39.9), Class III (40+).
Frequently Asked Questions
BMI is a reasonable screening tool for the general population but has significant individual limitations. It cannot distinguish muscle from fat — a bodybuilder and a sedentary person can have the same BMI with very different body compositions. It also doesn't account for age (older adults tend to have more fat), sex (women naturally carry more fat), or fat distribution (abdominal fat is riskier than other fat).
The WHO defines a healthy BMI as 18.5–24.9. However, some research suggests the optimal range varies by age and ethnicity. For example, some Asian populations may have increased health risks above 23, while Pacific Islander populations may have lower risks at BMIs up to 26. The 18.5–24.9 range is a general guideline, not a universal rule.
Yes — muscle is denser than fat, so someone with significant muscle mass will have a higher BMI than their body fat percentage would suggest. This is why BMI is less useful for athletes, bodybuilders, and people with high muscle mass. For these individuals, body fat percentage (measured by calipers, DEXA scans, or bioelectrical impedance) is more informative.
Yes — children's BMI is interpreted differently. Instead of fixed thresholds, children's BMI is compared to age-and-sex-specific growth charts (percentiles). A child at the 85th–95th percentile is considered overweight, and above the 95th percentile is obese. This calculator is designed for adults (18+). For children, use a CDC-based pediatric BMI calculator.
BMI can provide a rough target range, but it shouldn't be your only metric. The "healthy weight range" shown for your height gives a reasonable window. However, factors like muscle mass, bone density, overall fitness, and body fat distribution matter more for health outcomes. Consult a healthcare provider for personalized weight management advice.