Common BMI Questions
Expert answers to frequently asked questions about Body Mass Index.
What is BMI?
BMI stands for Body Mass Index. It is a simple calculation using a person's height and weight to measure tissue mass (muscle, fat, and bone) and screen for weight categories.
How do I calculate my BMI?
The formula is weight (kg) / [height (m)]^2. Alternatively, divide weight in pounds by height in inches squared and multiply by 703.
What is a normal BMI range?
A normal or healthy BMI range is generally considered to be between 18.5 and 24.9.
What BMI is considered overweight?
A BMI between 25.0 and 29.9 falls within the overweight range.
What BMI is considered obese?
A BMI of 30.0 or higher is considered obese. Obesity is further divided into Class 1, 2, and 3.
Is BMI accurate for athletes?
BMI can be misleading for athletes because muscle weighs more than fat. A bodybuilder may have a high BMI but low body fat.
Does BMI differentiate men/women?
The calculation is the same, but women naturally have more body fat than men at the same BMI score.
What is BMI Prime?
BMI Prime is the ratio of actual BMI to the upper limit of optimal BMI (25). < 0.74 is underweight.
Can I calculate BMI for children?
For children (2-19), BMI is interpreted using age-and-sex-specific percentiles, not just the raw number.
Why is BMI important?
It is an inexpensive screening method for weight categories which correlate with health risks like heart disease.
Risks of high BMI?
High BMI is linked to heart disease, type 2 diabetes, high blood pressure, and sleep apnea.
Risks of low BMI?
Underweight status can lead to malnutrition, osteoporosis, and weakened immune system.
Does age affect BMI?
Yes, older adults often have more body fat than younger adults at the same BMI.
How often to check BMI?
Checking once every few months is sufficient unless managing a specific weight program.
Is waist circumference important?
Yes. Measuring waist circumference helps screen for visceral fat risks alongside BMI.
Metric BMI formula?
BMI = kg / m². Weight in kilograms divided by height in meters squared.
Imperial BMI formula?
BMI = (lbs / in²) * 703. Weight in pounds divided by inches squared, multiplied by 703.
Normal BMI but high fat?
This is 'normal weight obesity' or 'skinny fat'—normal weight but low muscle mass.
What is my ideal weight?
Ideal weight depends on height. Reverse the BMI formula (target 18.5-24.9) to find your range.
Does pregnancy affect BMI?
Yes. Standard charts should not be used to assess weight status during pregnancy.
What is Ponderal Index?
Similar to BMI but divides weight by height cubed (m³). Better for very short/tall people.
Different charts for races?
Yes, Asian populations often use lower BMI cutoffs (overweight > 23) due to higher diabetes risk.
How accurate is this calculator?
It is mathematically accurate for the formula, but cannot assess body composition (muscle vs fat).
Can I lower BMI quickly?
Healthy weight loss is 1-2 lbs/week. Crash dieting causes muscle loss.
Average US BMI?
The average adult BMI in the US is approximately 29, which falls in the overweight category.
Does bone density affect BMI?
Yes, dense bones weigh more, potentially raising BMI without excess fat.
Convert 5'9" to meters?
5'9" is 69 inches. 69 * 2.54 = 175.26 cm, or roughly 1.75 meters.
What BMI is anorexia?
A BMI below 17.5 is often used as a physical indicator for diagnosis in adults.
Is BMI used for insurance?
Yes, life insurance premiums often increase for higher BMI categories.
What is Class 3 Obesity?
BMI of 40 or higher, formerly called 'morbid obesity'.
Does height affect life expectancy?
Height is less of a factor than BMI. Extremes at both ends of the BMI scale carry higher risks.
Why was BMI invented?
It was invented in the 1830s by Adolphe Quetelet for statistical sociology, not individual health.
BMI for very tall people?
BMI tends to overestimate fat in tall people. The New BMI formula (1.3 * weight / height^2.5) corrects this.
Healthy weight for 5'4" female?
Approx. 110 to 145 lbs (BMI 18.5-24.9).
Healthy weight for 5'10" male?
Approx. 130 to 173 lbs (BMI 18.5-24.9).
Do I need a doctor?
No for calculation, but yes for interpreting what it means for your specific health.
Can dehydration affect BMI?
Yes, dehydration lowers weight temporarily, lowering BMI.
Is 23 BMI good?
Yes, 23 is in the middle of the Normal range, associated with lowest health risks.
Does muscle weigh more than fat?
Muscle is denser than fat. A liter of muscle weighs more than a liter of fat.
What is the lowest healthy BMI?
18.5. Falling below this suggests being underweight.