BMI (Body Mass Index)

What is BMI (Body Mass Index)?

Weight-to-height ratio often used to classify weight status.

Why it matters

Simple screening metric for population health, though it ignores body composition.

How it works

BMI = weight (kg) / height (m)^2. Categories range from underweight to obesity.

A person weighing 70 kg at 1.75 m height has a BMI of approximately 22.9, falling in the normal weight range.
An athlete with high muscle mass might have a BMI over 25 but still have low body fat percentage.
A child or elderly person may have different BMI interpretations due to growth or muscle loss.
For a 5'5" (165 cm) person weighing 150 lbs (68 kg), BMI is about 25, which is overweight.
Pregnant women often have higher BMI due to increased weight, but it's not a reliable measure during pregnancy.

Treating BMI as a direct measure of body fat
Ignoring muscle mass and distribution
Using BMI for children without age-specific charts
Relying solely on BMI for health assessments without considering overall lifestyle
Comparing BMI across different ethnic groups without context

Is BMI accurate for everyone?

No, BMI doesn't distinguish between muscle and fat, so it can misclassify athletes or those with higher muscle mass.

What are the BMI categories?

Under 18.5: underweight, 18.5–24.9: normal, 25–29.9: overweight, 30+: obese.

How to calculate BMI?

Divide your weight in kilograms by your height in meters squared. Use our BMI calculator for instant results.

What is a healthy BMI?

A BMI between 18.5 and 24.9 is generally considered healthy for adults, but consult a healthcare provider for personalized advice.

BMI vs body fat percentage: which is better?

Body fat percentage is more accurate for assessing health, as BMI doesn't account for muscle mass or fat distribution.

Can BMI be used for children?

BMI percentiles are used for children, adjusted for age and sex, as growth patterns vary.

What are the limitations of BMI?

BMI doesn't measure body fat directly and can be misleading for athletes, pregnant women, or those with certain medical conditions.

How often should I check my BMI?

Check periodically, especially during weight changes, but focus on overall health markers like blood pressure and cholesterol.

What BMI is considered obese?

A BMI of 30 or higher is classified as obese.

Does BMI differ by gender?

The formula is the same, but body composition varies; women may have higher body fat at the same BMI.

How does BMI relate to health risks?

Higher BMI correlates with increased risks for conditions like diabetes and heart disease, but it's not the only factor.

Can I have a normal BMI and still be unhealthy?

Yes, if you have high body fat or poor fitness levels despite normal BMI.

What is BMI used for in medicine?

Doctors use BMI for initial screening, but combine it with other tests for comprehensive health evaluation.