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BMI Calculator

What the BMI Calculator does

The BMI Calculator works out Body Mass Index from your height and weight, in either metric or imperial units, and tells you which standard weight category (underweight, normal, overweight, obese) that BMI falls into according to WHO reference ranges.

How to use it

  1. Choose your unit system (metric or imperial).
  2. Enter your weight and height.
  3. Click Calculate BMI to see your BMI value and weight category.

Common uses

  • Getting a quick, general sense of whether weight falls in a typical healthy range for height.
  • Tracking BMI changes over time alongside a fitness or nutrition goal.
  • Checking BMI as one input ahead of a doctor's appointment or health screening.
  • Comparing BMI calculated in metric vs. imperial units for consistency.
  • Educational use in health or biology coursework covering body composition metrics.

Good to know

BMI is a population-level screening measure, not a diagnostic tool — it doesn't distinguish muscle mass from fat mass, so athletes and very muscular individuals often show a "high" BMI despite low body fat. For an individual health assessment, BMI is best treated as one data point to discuss with a healthcare provider rather than a standalone verdict.

BMI became a widely used screening tool largely because it's simple to calculate from just two measurements, which made it practical for large-scale public health studies long before more sophisticated body composition tools (like DEXA scans or bioelectrical impedance) were widely available. That historical convenience is also its core limitation today — it's a population-level statistical tool being applied to individuals, which is why most clinicians treat a BMI reading as one input among several rather than a standalone diagnosis.

Frequently asked questions

For most adults, a BMI between 18.5 and 24.9 is considered within the healthy weight range, according to WHO guidelines.

BMI is a useful general screening measure, but it does not account for muscle mass, bone density, or body composition, so athletes and some individuals may see skewed results.