Calculate your Body Mass Index (BMI), see your WHO weight category, healthy weight range for your height, and understand what your BMI means for your health.
Body Mass Index (BMI) is a widely used screening tool that estimates body fat based on the simple relationship between your weight and height. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, it remains the most common first-step assessment used by doctors, researchers, and public health organizations worldwide.
This calculator computes your BMI using either imperial (pounds, feet/inches) or metric (kilograms, centimeters) measurements. It shows your numeric BMI value, the corresponding WHO weight category (Underweight, Normal, Overweight, or Obese classes I-III), and the healthy weight range for your specific height. A color-coded visual scale makes it easy to see where you fall.
While BMI is not a direct measure of body fat and has known limitations (it may overestimate fat in muscular individuals and underestimate it in older adults), it remains a quick, free, and evidence-based starting point for assessing weight-related health risks. Major studies consistently show that BMIs in the 18.5-24.9 range are associated with the lowest health risks for most adults.
Knowing your BMI gives you an objective, numbers-based starting point for health conversations with your doctor. It takes seconds to calculate and provides immediate context: Am I in a healthy range? How far am I from the recommended range? What would I need to weigh to reach a normal BMI?
It is especially useful when tracking weight over time. Changes in BMI help you measure progress during weight loss or fitness programs and ensure you are moving in a healthy direction.
Metric: BMI = weight (kg) / [height (m)]² Imperial: BMI = [weight (lbs) × 703] / [height (inches)]² WHO Categories: < 18.5 = Underweight 18.5 – 24.9 = Normal weight 25.0 – 29.9 = Overweight 30.0 – 34.9 = Obese Class I 35.0 – 39.9 = Obese Class II ≥ 40.0 = Obese Class III
Result: BMI: 24.4 — Normal weight
A person weighing 170 lbs at 5'10" (70 inches) has a BMI of 24.4, which falls in the "Normal weight" category (18.5–24.9). The healthy weight range for this height is 129–174 lbs. This person is near the upper end of normal and would be classified as overweight at 175 lbs.
BMI was created by Adolphe Quetelet in the early 19th century as a statistical tool for studying populations, not individuals. It was adopted by insurance companies in the mid-20th century and formalized by the WHO in 1995 as a simple screening metric. Despite its limitations, no equally simple alternative has replaced it for population-level health assessment.
BMI does not distinguish between muscle mass and fat mass, does not account for fat distribution (abdominal fat is more dangerous than hip fat), and does not consider age, sex, or ethnicity. Two people with identical BMIs can have very different health risk profiles. It works best as a starting point, not a final verdict.
For a more complete picture, consider: waist-to-hip ratio (WHR), waist circumference, body fat percentage (via calipers, bioelectrical impedance, or DEXA scan), and lean body mass calculations. These metrics, combined with BMI, give healthcare providers a much richer understanding of your body composition and health risks.
The WHO defines a healthy BMI as 18.5 to 24.9 for adults. Below 18.5 is underweight; 25.0-29.9 is overweight; 30.0+ is obese. Within the normal range, research suggests 22-23 is associated with the lowest health risks.
BMI can overestimate body fat in muscular individuals because muscle weighs more than fat per unit volume. A bodybuilder at 5'10" and 220 lbs would have a BMI of 31.6 (obese) despite potentially having very low body fat. Athletes should use body fat percentage or DEXA scans instead.
Children and teens use BMI-for-age percentile charts that account for normal growth patterns. A child's BMI is plotted against age- and sex-specific charts from the CDC or WHO. This calculator is designed for adults (18+).
Overweight and obese BMIs are associated with increased risk of type 2 diabetes, heart disease, high blood pressure, stroke, sleep apnea, certain cancers, and joint problems. Risk increases progressively with higher BMI.
A BMI below 18.5 carries its own health risks: weakened immune system, osteoporosis, anemia, fertility issues, and malnutrition. If your BMI is consistently below 18.5, consult a healthcare provider.
Waist circumference measures abdominal (visceral) fat, which is more closely linked to metabolic disease than overall body fat. Guidelines suggest risk increases above 40 inches for men and 35 inches for women. Ideally, use both BMI and waist circumference together.
Monthly is sufficient for tracking trends. Daily weight fluctuations of 1-3 lbs are normal due to water retention, food intake, and exercise. Focus on the long-term trend rather than any single measurement.