| Category | BMI Range | Health Context |
|---|---|---|
| Underweight | Below 18.5 | May indicate nutritional deficiency; consult a healthcare provider. |
| Normal Weight | 18.5 – 24.9 | Associated with lower risk for most weight-related health conditions. |
| Overweight | 25.0 – 29.9 | Elevated risk for cardiovascular disease, type 2 diabetes, and joint stress. |
| Obese — Class I | 30.0 – 34.9 | Increased risk for metabolic syndrome, sleep apnea, and hypertension. |
| Obese — Class II | 35.0 – 39.9 | High risk; weight management and medical supervision strongly advised. |
| Obese — Class III | 40.0 and above | Severe obesity; associated with significantly elevated all-cause mortality risk. |
Select your preferred unit system — Imperial (feet, inches, and pounds) or Metric (centimeters and kilograms). Enter your height and weight, then click Calculate My BMI. Your BMI, weight category, and healthy weight range for your height appear instantly. You can switch between Imperial and Metric at any time without losing your inputs. The calculator uses the standard CDC and WHO formulas and category thresholds.
Body Mass Index (BMI) is a numerical value derived from your height and weight that provides a rough estimate of body fatness. Developed in the 1830s by Belgian mathematician Adolphe Quetelet, it became a standard medical screening tool in the 20th century because it's inexpensive to calculate, requires no equipment, and correlates reasonably well with body fat percentage at the population level.
The formula is simple: in metric, BMI equals weight in kilograms divided by height in meters squared. In imperial units, it equals weight in pounds multiplied by 703, divided by height in inches squared. The resulting number places you in one of several WHO-defined categories that correlate with health risk — from underweight to severely obese.
The World Health Organization and CDC define five standard BMI categories for adults. A BMI below 18.5 is Underweight, associated with nutritional deficiencies, weakened immune function, and reduced bone density. 18.5 to 24.9 is Normal or Healthy weight — the range associated with the lowest average risk for weight-related disease. 25.0 to 29.9 is Overweight, associated with increased risk for cardiovascular disease, type 2 diabetes, and certain cancers. A BMI of 30 or higher is Obese, further divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+), with escalating health risks at each level.
BMI is a population-level screening tool with well-documented limitations when applied to individuals. It cannot distinguish between fat mass and lean muscle mass — a strength athlete with very low body fat may have the same BMI as someone with obesity. It also does not account for where fat is distributed on the body; visceral fat (around the abdomen) carries significantly higher health risk than subcutaneous fat, but BMI measures neither. Age, sex, and ethnicity also affect the relationship between BMI and body fat percentage in ways the formula cannot capture. For a complete health picture, BMI should be considered alongside waist circumference, body composition testing, blood pressure, lipid panel, and blood glucose.
The standard BMI thresholds (18.5–24.9 for healthy) were derived from studies of predominantly European populations. Research has shown that people of Asian descent tend to have higher body fat percentages at the same BMI, which has led some health organizations to recommend lower thresholds (like 23 for overweight) for Asian adults. For older adults, a slightly higher BMI may be protective against bone density loss and frailty. Children and teenagers require age- and sex-specific BMI-for-age percentiles, not the adult thresholds used in this calculator.
For most adults over 20, the WHO defines a healthy BMI as 18.5 to 24.9. Within this range, the risk of developing weight-related conditions is generally lowest. However, "healthy" at the individual level depends on far more than this single number. A BMI of 25 does not automatically mean you need to lose weight, and a BMI of 22 does not guarantee good health. The healthy weight range this calculator provides is the range of weights corresponding to a BMI of 18.5–24.9 for your specific height — it's a useful reference point, not a medical prescription.
If your BMI falls outside the 18.5–24.9 range, it's worth discussing with a healthcare provider, but the urgency depends on how far outside the range you are and what other health markers look like. A BMI of 26 in an otherwise healthy, active person may not warrant immediate intervention. A BMI of 35 with elevated blood pressure, high blood glucose, and a family history of heart disease is a more pressing concern. Your doctor can interpret your BMI in context, order appropriate tests, and help you set realistic, evidence-based goals for weight management if needed.
Expert guides and educational resources to help you master the math.
BMI = (weight lbs × 703) ÷ height inches². But it doesn't measure fat, muscle, or fat distribution — and uses different risk thresholds for different ethnicities. Here's what it means and what to measure instead.
A 500-calorie daily deficit produces roughly 1 lb/week — but your actual target depends on TDEE. Here's the Mifflin-St Jeor formula, activity multipliers, and why everyone eventually hits a plateau.
