Calculation Results
BMI: 0.00
BMI Category:
BMI Prime: 0.00
Over/Under Limit:
Hazard Ratio for All-Cause Mortality (Men): No data available
Hazard Ratio for All-Cause Mortality (Women): No data available
BMI Calculator
What Body Mass Index Measures
Body mass index condenses height and weight into one screening number. Clinics, insurers, coaches, and researchers use it to sort adults into broad weight categories within seconds. It is not a direct measure of body fat, yet it reliably flags when weight might deserve a closer look.
The calculator accepts kilograms and centimeters or pounds and inches, so the result arrives in whichever units you already know. Because the formula is standardized worldwide, your score compares cleanly across clinics, apps, and insurance forms. A score near 22 also anchors related tools that estimate daily calories or target weight.
The Formula and a Worked Example
In metric units, body mass index equals weight in kilograms divided by height in meters squared. Take an adult weighing 70 kilograms at 1.75 meters: height squared is 1.75 times 1.75, or 3.0625, and dividing 70 by 3.0625 gives about 22.9, comfortably inside the normal category.
Adult categories are fixed: under 18.5 is underweight, 18.5 to 24.9 is normal, 25 to 29.9 is overweight, and 30 or higher is obese. The same cutoffs apply to adult men and women of every background.
Using the Calculator Well
Choose Imperial or Metric under Unit System, then type your measurement into the Height and Weight boxes. Press Calculate BMI and the score plus its category appear immediately. Weigh yourself at a consistent time, ideally in the morning, so repeated checks track real change rather than daily swings.
Remember the classic pitfall: very muscular people often score high because muscle outweighs fat, so large athletes can read as overweight despite low body fat. Pair the number with waist size or a body fat test, and let a clinician interpret it alongside your history.
Frequently Asked Questions
How is BMI calculated exactly?
Body mass index equals weight in kilograms divided by height in meters squared. For 70 kilograms at 1.75 meters, the math is 70 divided by 3.0625, which gives approximately 22.9, a normal result.
What BMI number counts as obese?
A body mass index of 30 or higher is obese for adults, with 25 to 29.9 classed as overweight. Severe obesity usually starts at 35, and 40 plus is class 3 obesity.
Is BMI accurate for muscular athletes?
Often no. Muscle is denser than fat, so a well trained athlete can register 27 or 28 while carrying very little body fat. Waist circumference or a body fat test offers a fairer picture for very active people.
Do children use the same BMI cutoffs?
No. Children and teenagers are screened with age and sex specific percentile charts because body composition shifts as they grow. The fixed adult categories on this page apply from age 20 onward.
How often should I check my BMI?
For most adults, a check every month or two is plenty. Weight drifts slowly, so occasional tracking reveals trends without encouraging obsession over a screening number that barely moves day to day.