BMI Calculator

What is BMI?

Body Mass Index (BMI) is a simple numerical measure that relates your weight to your height. It is widely used as a screening tool to identify whether an adult is underweight, at a healthy weight, overweight, or obese. Although BMI does not measure body fat directly, it gives a quick estimate of potential health risks related to weight.

BMI Categories and Health Risks

Category	BMI Range	Health Risk
Underweight	< 18.5	Increased risk of malnutrition, osteoporosis, and weakened immunity.
Healthy Weight	18.5 – 24.9	Lowest overall health risk for most adults.
Overweight	25.0 – 29.9	Higher chance of developing diabetes, heart disease, and joint problems.
Obesity (Class I)	30.0 – 34.9	Elevated risk of cardiovascular and metabolic conditions.
Obesity (Class II)	35.0 – 39.9	Serious risk of obesity-related illnesses.
Extreme Obesity (Class III)	≥ 40.0	Very high risk of severe health complications and reduced life expectancy.

What is a BMI Calculator?

A BMI Calculator is an online tool that applies the BMI formula for you. By entering your weight, height, and preferred unit system (imperial or metric), it instantly provides your BMI value, identifies the BMI category, and shows the corresponding healthy weight range. This helps you better understand your weight status without doing the math manually.

How to Use a BMI Calculator

Select your measurement system: Imperial (lbs, ft/in) or Metric (kg, cm).
Enter your weight and height accurately.
Click the Calculate button to get your BMI value and category.
Review the healthy weight range provided for your height.

For those who prefer manual calculation:

Metric formula: BMI = weight (kg) ÷ [height (m)]²

Imperial formula: BMI = 703 × weight (lbs) ÷ [height (in)]²

Important Limitations of BMI

While BMI is a convenient tool, it has several important limitations:

Doesn't measure body fat directly: A muscular athlete may have a high BMI but very low body fat.
Doesn't show fat distribution: Central fat around the waist is more dangerous than fat in other areas.
Varies by age and sex: Older adults and women may have different health risks at the same BMI as younger adults or men.
Ethnic differences: Some populations face health risks at lower BMI thresholds.

Beyond BMI: Other Important Health Indicators

To get a full picture of your health, BMI should be combined with other measures:

Waist circumference — shows abdominal fat risk.
Waist-to-hip ratio — another indicator of fat distribution.
Body fat percentage — measured with calipers, smart scales, or DEXA scans.
Blood pressure and blood sugar — critical for cardiovascular and metabolic health.
Lipid profile — cholesterol and triglycerides help identify heart disease risk.

Frequently Asked Questions (FAQ)

How do I calculate BMI manually?

Use the formula:BMI = 703 × weight (lbs) ÷ [height (in)]²

Example: A person weighing 150 lbs at 65 inches tall has a BMI of 25.0.

Is BMI accurate for athletes?

Not always. Because BMI does not distinguish muscle from fat, athletes with high muscle mass may appear "overweight" by BMI even though their body fat is low.

Does BMI apply to children and teens?

For people under 19, BMI is interpreted using age- and sex-specific percentiles, not the adult cutoffs. Pediatric charts and a doctor's input are recommended.

How often should I check my BMI?

Checking every few months is fine for most adults. If you're actively trying to lose or gain weight, you may track it more frequently, but focus on long-term trends.

What BMI is considered "healthy"?

For adults, a BMI between 18.5 and 24.9 is considered the healthy range, though other health factors should also be taken into account.

Are there better measures than BMI?

Yes. Body fat percentage, waist-to-hip ratio, waist circumference, and lab tests like cholesterol or blood sugar often provide more useful insights than BMI alone.

Should older adults aim for the same BMI as younger adults?

Older adults may have different health outcomes at the same BMI. Some research suggests that slightly higher BMI ranges may not carry the same risks for seniors.