BMI Calculator – Free Body Mass Index Calculator
Body Mass Index compares your weight with your height and puts the answer in a standard category. Doctors and researchers lean on it because the inputs are quick and objective, and because large population studies link BMI ranges to health risk.
Our version works for adult men and women, switches between metric and US units, and additionally reports the weight range that would put you inside the normal band for your height.
How BMI Is Calculated
The formula divides weight in kilograms by height in metres squared: BMI = kg / m2. In US units, the same result comes from 703 × lb / in2. A 1.75 m adult weighing 78 kg lands at 25.5.
Results fall into World Health Organization categories: under 18.5 is underweight, 18.5–24.9 is the normal range, 25–29.9 is overweight, and 30 or above falls inside the obese classes.
Limitations Worth Knowing
BMI measures mass, not composition. Muscle is denser than fat, so strength athletes, sprinters and manual workers are routinely pushed into the overweight bracket with perfectly healthy levels of body fat. Age matters too: two people with identical BMI can carry quite different amounts of fat.
Use it as the useful screening tool it is — then add context. Waist circumference, blood pressure, blood lipids, and your estimated body fat percentage together paint a much clearer picture than any single number.
Frequently Asked Questions
Is BMI accurate for bodybuilders?
Not especially. Extra muscle lifts body weight without any rise in fat, so muscular physiques are regularly overclassified. Combine BMI with waist measurement or a body fat estimate before drawing conclusions.
Should BMI alone decide whether I am healthy?
No. Look at waist size, energy levels, sleep, blood work and how much you move each week. BMI is one inexpensive signal among several, never the verdict.
Does the healthy BMI range change with age?
The standard categories are fixed for adults, though research suggests slightly higher values carry lower risk in older adults. Children and teenagers use age-adjusted growth charts instead.
What BMI should I aim for?
Rather than chasing a BMI figure, pick a rate of change you can hold: about 0.5–1% of body weight per week. Use our TDEE calculator to set the calories that get you there.
Results come from published population equations and are estimates only — they are not medical advice. See our disclaimer.
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