How this tool fits your workflow
What BMI measures and what it does not
Body Mass Index is a ratio of weight to the square of height. It was designed as a population-level screening tool in the 19th century. At the population level, higher BMI correlates with increased risk of type 2 diabetes and cardiovascular disease. At the individual level, the correlation is weaker because BMI ignores body composition.
A bodybuilder with significant muscle mass will have a high BMI but low body fat. An elderly person with low muscle mass may have a normal BMI but high visceral fat. For routine health tracking and quick screening, BMI is useful and widely understood. For clinical decisions, combine it with waist circumference, body fat percentage, and metabolic markers.
BMI categories and their thresholds
Standard adult BMI categories: Underweight (below 18.5), Normal weight (18.5 to 24.9), Overweight (25.0 to 29.9), Obese Class I (30.0 to 34.9), Obese Class II (35.0 to 39.9), Obese Class III (40.0 and above). These cutoffs are the same for men and women in most clinical contexts, though some guidelines use adjusted thresholds for Asian populations starting at 23.0 for overweight.
Frequently asked questions
- What is a healthy BMI range?
- For adults, a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is underweight, 25-29.9 is overweight, and 30 or above is obese per WHO guidelines.
- Is BMI accurate for everyone?
- BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age, or sex. Athletes may have high BMI despite low body fat.
- What is the BMI formula?
- BMI = weight (kg) divided by height squared (m^2) in metric. In imperial: BMI = 703 times weight (lb) divided by height squared (in^2).
- Can I calculate BMI for children?
- This calculator is designed for adults. For children and teens, BMI uses age and sex-specific percentiles. Consult a pediatrician for youth BMI assessment.