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Your BMI tells you whether your current weight falls within a healthy range for your height  in under 10 seconds. Enter your height and weight above to get your result, your WHO weight category, and exactly what your number means for your health.

What Is BMI (Body Mass Index)?

BMI, or Body Mass Index, is a number calculated from your height and weight that estimates whether you carry a healthy amount of body weight. A BMI of 18.5 to 24.9 is considered the healthy range for most adults.

The index was developed in the 1830s by Belgian statistician Adolphe Quetelet as a simple population-level screening tool. While it was never intended as a diagnostic measure, the World Health Organization (WHO) and the CDC both use BMI as a standard first-step indicator of weight-related health risk.

In 2023, the American Medical Association added a formal statement acknowledging BMI's limitations  but also confirmed it remains "a useful measure for population-level data" when understood in context.

BMI is not a measure of body fat directly. It is a ratio of weight to height. Two people with identical BMIs can have vastly different body compositions, which is why BMI works best as one of several health indicators, not the only one.

Why BMI Is Still Used by Doctors in 2025

Despite its critics, BMI persists in clinical settings for a simple reason: it is fast, free, non-invasive, and strongly correlated with weight-related conditions at population scale.

According to the CDC, adults with a BMI over 30 face significantly higher risk of type 2 diabetes, cardiovascular disease, sleep apnea, and certain cancers. BMI provides a consistent benchmark that requires no blood test, no scan, and no specialist  making it accessible to any healthcare provider worldwide.

BMI vs. Body Fat Percentage  Key Differences

BMI uses only height and weight. Body fat percentage measures the actual proportion of fat mass versus lean mass in your body. For most people, BMI and body fat percentage correlate reasonably well. The gap widens for athletes (high muscle mass makes BMI appear high) and older adults (BMI can appear normal while body fat percentage is actually elevated).

The BMI Formula How Body Mass Index Is Calculated

BMI = weight ÷ height²

The formula is the same whether you use metric or imperial units  the only difference is the unit conversion factor.

BMI Formula in Metric Units (kg and cm)

BMI = weight (kg) ÷ height (m)²

Note: height must be in meters, not centimeters. Convert by dividing cm by 100.

Example conversion: 175 cm = 1.75 m

BMI Formula in Imperial Units (lbs and inches)

BMI = 703 × weight (lbs) ÷ height (inches)²

The 703 is a conversion constant that adjusts for the difference between metric and imperial units.

Step-by-Step BMI Calculation Example

Example: Person weighing 154 lbs (70 kg), height 5 ft 7 in (170 cm)

Metric method:

1. Convert height: 170 cm ÷ 100 = 1.70 m
2. Square the height: 1.70 × 1.70 = 2.89
3. Divide weight by result: 70 ÷ 2.89 = BMI 24.2

Imperial method:

1. Convert height to inches: 5 ft 7 in = 67 inches
2. Square the height: 67 × 67 = 4,489
3. Multiply weight by 703: 154 × 703 = 108,262
4. Divide: 108,262 ÷ 4,489 = BMI 24.1

(Small rounding difference is normal between metric and imperial calculations.)

Result: BMI 24.2  Normal weight range. 

How to Use This BMI Calculator

Using the BMI calculator above takes under 30 seconds. No sign-up, no fees, no data saved.

Input Fields Explained

Toggle between imperial (ft, lbs) and metric (cm, kg) using the unit switcher at the top of the calculator.

How to Read and Interpret Your BMI Result

Your result shows three things:

1. Your BMI number  one decimal place for precision
2. Your WHO weight category  underweight, normal, overweight, or obese
3. Your position on the range bar  a visual indicator of where you fall within each category

A BMI between 18.5 and 24.9 means your weight is in the range statistically associated with the lowest health risk. Numbers outside this range are not a diagnosis  they are a signal to discuss with your doctor.

BMI Categories  What Does Your Number Mean?

WHO BMI Classification Table

Source: World Health Organization Global BMI Classification, 2024

BMI Ranges by Age and Sex

BMI cut-off points were established using data predominantly from white European adults. Research published in the International Journal of Obesity suggests that Asian adults face higher metabolic risk at lower BMI values  the WHO now recommends a lower overweight threshold (23.0) for Asian populations.

For adults over 65, a BMI between 25 and 27 may actually be protective against bone density loss and frailty, according to NIH-published research from 2022.

Real-World BMI Examples

Example 1  Adult Woman, Average Height

Profile: 38-year-old woman, 5 ft 4 in (163 cm), 145 lbs (65.8 kg)

Calculation:

• Height in meters: 1.63 m
• Height squared: 2.66
• BMI = 65.8 ÷ 2.66 = 24.7

Result: Normal weight (just within range). No intervention needed based on BMI alone.

Example 2  Tall Adult Man

Profile: 29-year-old man, 6 ft 2 in (188 cm), 210 lbs (95.3 kg)

Calculation:

• Height in meters: 1.88 m
• Height squared: 3.53
• BMI = 95.3 ÷ 3.53 = 27.0

Result: Overweight category. For a muscular man of this height, further assessment (waist circumference, body fat measurement) would provide more accurate health insight than BMI alone.

Limitations of BMI  When the Number Can Mislead

BMI has real blind spots. Understanding them helps you use the tool accurately.

BMI for Athletes and Muscular Individuals

Muscle is denser than fat. A trained athlete can carry significantly more lean muscle mass than the average person, pushing their BMI into the "overweight" range despite having very low body fat. The CDC explicitly notes that BMI "may overestimate body fat in athletes."

If you are highly active or muscular, combine your BMI with waist circumference measurement or a body fat assessment for a more accurate picture.

BMI for Older Adults and Ethnic Groups

As people age, muscle mass naturally decreases while fat mass increases  a process called sarcopenic obesity. This means an older adult can have a "normal" BMI while carrying excess fat and insufficient muscle.

Additionally, research shows BMI underestimates health risk in South Asian, East Asian, and Hispanic populations at the same BMI values as white European populations. If you fall into these groups, speak with your doctor about adjusted reference ranges.