BMI Calculator
Calculate your Body Mass Index and weight category — underweight, normal, overweight, or obese — based on height and weight.
How to use this bmi calculator
- 1Enter your weight in pounds. Use your morning weight for the most consistent reading.
- 2Enter your height in inches — convert feet and inches first (5 ft 8 in = 68 in).
- 3Your BMI and weight category appear instantly along with your healthy weight range.
- 4Use BMI as a screening tool, not a diagnosis. Follow up with a healthcare provider for a complete health assessment.
- 5Track BMI changes over time rather than fixating on a single reading — trends matter more than any one number.
How it's calculated
BMI = (weight in lb / height² in inches) × 703. Categories: <18.5 underweight · 18.5–24.9 normal · 25–29.9 overweight · 30+ obese.
About the BMI Calculator
BMI is one of the most widely used and most frequently misunderstood tools in medicine. It was never designed to assess individual health — it was a statistical measure for comparing population weights developed by Belgian mathematician Adolphe Quetelet in the 1830s. It was adopted by public health in the 1970s because it requires only two easy measurements: height and weight.
Despite its limitations, BMI provides genuinely useful information for most adults. The strong statistical association between high BMI and adverse health outcomes — type 2 diabetes, hypertension, cardiovascular disease, sleep apnea, certain cancers, osteoarthritis — is well established across thousands of studies involving millions of participants. These associations exist even after adjusting for confounders. At the same time, numerous studies find metabolically healthy obese individuals and metabolically unhealthy normal-weight individuals, confirming that BMI is not destiny.
For practical health monitoring, BMI works best as one component of a broader assessment. Combine it with waist circumference (measures abdominal fat specifically), blood pressure, fasting blood glucose, lipid panel, and cardiorespiratory fitness for a meaningful picture of metabolic health. A physically active person with BMI 27 and normal metabolic markers may be healthier than a sedentary person with BMI 23 and pre-diabetic blood sugar.
The most actionable takeaway from BMI is not the category label but the direction of change. Someone moving from BMI 32 to 29 has meaningfully reduced health risk even while remaining in overweight territory. Progress matters more than perfection when it comes to weight-related health outcomes.
Frequently asked questions
What is BMI and what does my number mean?
BMI (Body Mass Index) is a screening tool that estimates body fatness based on height and weight. A BMI of 18.5–24.9 is normal weight and associated with the lowest health risks in population studies. Below 18.5 is underweight, 25–29.9 is overweight, and 30+ is obese (with three sub-classes). These thresholds predict health risk at the population level, but individual risk depends on many factors beyond BMI including age, sex, ethnicity, fitness level, and fat distribution.
Is BMI accurate for athletes and muscular people?
No — BMI does not distinguish between muscle mass and fat mass, making it systematically misleading for muscular individuals. A professional athlete may have a BMI of 30–32 (classified as obese) while having very low body fat and exceptional health. Conversely, someone with a normal BMI of 23 may have high visceral fat and metabolic dysfunction — called normal weight obesity. For athletes and highly muscular individuals, body fat percentage measurement (DEXA scan, hydrostatic weighing, or the Navy Method) is far more informative than BMI.
Does BMI apply equally to all ethnicities?
No. Research shows health risks associated with overweight occur at lower BMI thresholds in some ethnic groups. Asian populations show increased cardiometabolic risk at BMI 23+ compared to 25+ in European populations, and the WHO has proposed lower thresholds for Asian patients. Many healthcare organizations now use ethnicity-adjusted BMI thresholds. Conversely, some studies suggest Black adults may carry higher lean mass at equivalent BMIs, potentially making standard thresholds less accurate for this group as well.
What is a healthy BMI for women vs men?
The standard BMI thresholds apply to both men and women. However, women naturally carry a higher percentage of body fat than men at any given BMI — healthy body fat for adult women is approximately 20–32%, while for men it is 8–20%. This means at the same BMI, women and men have different underlying body compositions. Some researchers argue for sex-specific BMI thresholds, but current clinical guidelines use the same ranges for all adults regardless of sex.
How much weight do I need to lose to move to a lower BMI category?
The weight change needed depends on your height. At 5 ft 8 in (68 inches), moving from overweight (BMI 27) to normal requires losing approximately 14 pounds. Use the healthy weight range shown in this calculator to find the target zone for your height. Research shows that even a 5–10% reduction in body weight produces clinically meaningful improvements in blood pressure, blood sugar, cholesterol, and joint pain — you do not need to reach a normal BMI to benefit significantly.
Is BMI a good predictor of health risks?
BMI is a useful population-level screening tool but an imperfect individual predictor. It correlates with risk of type 2 diabetes, cardiovascular disease, certain cancers, sleep apnea, and joint disease at the population level. However, waist circumference is often a better predictor of cardiometabolic risk because it measures abdominal visceral fat specifically. A waist circumference above 40 inches in men or 35 inches in women signals elevated risk regardless of BMI. Combining BMI with waist circumference provides a better health picture than either alone.