BMI Calculator
Calculate Body Mass Index and ideal weight
How to use BMI Calculator
Calculate your Body Mass Index (BMI) and find your ideal weight range. Supports metric and imperial units. Free online tool.
What is BMI used for?
Body Mass Index (BMI) is a screening tool that uses height and weight to assess whether a person falls into a healthy weight range. It is widely used in public health, clinical settings, and research — though it has well-documented limitations.
- Healthcare screening: Doctors use BMI as a quick initial assessment of weight-related health risk. High BMI is associated with increased risk of type 2 diabetes, cardiovascular disease, and certain cancers.
- Public health statistics: BMI enables population-level obesity tracking and policy decisions without individual body composition measurements.
- Insurance: Some insurers use BMI as one factor in health and life insurance underwriting.
- Personal health tracking: Monitor weight changes over time relative to height — more informative than weight alone.
- Fitness goals: Set weight targets based on a healthy BMI range, understanding that muscle mass is denser than fat.
BMI categories (WHO): Under 18.5 = underweight. 18.5-24.9 = normal weight. 25-29.9 = overweight. 30+ = obese. These thresholds were developed from studies primarily on European populations and may not be optimal for all ethnicities.
Frequently Asked Questions
Is BMI an accurate measure of health?
BMI is a useful population-level screening tool but has significant limitations for individuals. It does not distinguish between fat and muscle mass — a highly muscular athlete may have a 'overweight' BMI despite low body fat. It also does not measure fat distribution; visceral fat (around organs) is more harmful than subcutaneous fat. BMI is best used alongside other assessments.
What is the difference between BMI and body fat percentage?
BMI is calculated from height and weight only — it is an estimate. Body fat percentage measures the actual proportion of fat mass to total body mass, measured by DEXA scan, hydrostatic weighing, or bioelectrical impedance. Body fat percentage is more accurate but requires specialized equipment.
Should children use the same BMI chart as adults?
No. Children's BMI is interpreted differently — it is plotted on age- and sex-specific growth charts and expressed as a percentile rather than a fixed category. A BMI that is healthy for a 35-year-old adult may be high for a 10-year-old.
Does ethnicity affect BMI interpretation?
Yes. Research suggests that Asian populations have higher health risks at lower BMI values. The WHO has proposed adjusted thresholds for Asian populations: overweight at 23 (vs 25) and obese at 27.5 (vs 30). Some health organizations in Asia use these adjusted thresholds.
What is the healthiest BMI range?
The standard healthy range is 18.5-24.9. Research on longevity suggests the lowest mortality is associated with a BMI of 22-23 for most adults. BMI slightly above 25 (overweight range) may actually be associated with lower mortality in older adults — this is known as the 'obesity paradox'.
BMI vs waist-to-height ratio vs body fat percentage vs waist circumference
BMI is the simplest to calculate — just height and weight. Waist circumference (above 88cm/35in for women, 102cm/40in for men indicates high risk) directly measures abdominal fat — a better predictor of metabolic disease than BMI. Waist-to-height ratio (waist/height < 0.5 is the healthy target) is considered more accurate than BMI across ethnicities. Body fat percentage via DEXA scan is the gold standard but expensive. For everyday monitoring, BMI is a reasonable starting point — just use it alongside waist measurement for a more complete picture.