# BMI Calculator

> Calculate your Body Mass Index (BMI) and check your weight classification.

## What is this calculator?

The BMI (Body Mass Index) Calculator is a health assessment tool that uses your height and weight to compute your Body Mass Index — a widely used screening metric for categorizing weight status. BMI was developed by Belgian mathematician Adolphe Quetelet in the 1830s and has been adopted globally by healthcare organizations as a quick, non-invasive indicator of whether a person's weight is within a healthy range relative to their height. This calculator provides classifications based on two standards: the WHO (World Health Organization) international standard, which is primarily derived from studies of Western populations, and the Asian standard established by the WHO Western Pacific Regional Office, which uses lower thresholds to account for the higher metabolic risk that Asian populations face at the same BMI levels. Research has consistently shown that Asian individuals tend to have higher body fat percentages and greater visceral fat accumulation at any given BMI compared to their Western counterparts, leading to increased risks of type 2 diabetes, cardiovascular disease, and metabolic syndrome at lower BMI values. This is why the Asian standard classifies BMI 23-24.9 as overweight and 25+ as obese, compared to the WHO standard's 25-29.9 and 30+ thresholds. In addition to your BMI category, this calculator displays your normal weight range — the minimum and maximum weight values that would place you in the normal BMI category for your height — providing a concrete target for weight management.

## How to use

Step 1: Enter your height in centimeters. Stand up straight without shoes for the most accurate measurement. If you know your height in feet and inches, you can convert by multiplying feet by 30.48 and adding inches multiplied by 2.54. For example, 5 feet 8 inches = (5 x 30.48) + (8 x 2.54) = 152.4 + 20.32 = 172.72 cm.

Step 2: Enter your weight in kilograms. For the most accurate result, weigh yourself in the morning before eating, wearing minimal clothing. If you know your weight in pounds, divide by 2.205 to convert to kilograms. For example, 154 pounds / 2.205 = 69.8 kg.

Step 3: Your BMI is calculated and displayed automatically, along with your weight classification under both WHO international and Asian standards. The calculator also shows the normal weight range for your height — this is the range of weights that would give you a BMI between 18.5 and 22.9 (Asian standard) or 18.5 and 24.9 (WHO standard).

Interpreting Your Results: BMI is a screening tool, not a diagnostic tool. A high BMI suggests that further assessment may be warranted (such as body fat percentage measurement, waist circumference, or blood work), but it does not definitively indicate that a person is unhealthy. Conversely, a normal BMI does not guarantee good health. Always consult a healthcare professional for a comprehensive health assessment that considers your complete medical history, lifestyle, and body composition.

## Formula

BMI = Weight (kg) / [Height (m)]^2

Or equivalently: BMI = Weight (kg) / (Height (cm) / 100)^2

Example: For a person who is 175 cm tall and weighs 72 kg:
BMI = 72 / (1.75)^2 = 72 / 3.0625 = 23.5

WHO International Classification:
- Underweight: BMI < 18.5
- Normal weight: BMI 18.5 - 24.9
- Overweight: BMI 25.0 - 29.9
- Obese Class I: BMI 30.0 - 34.9
- Obese Class II: BMI 35.0 - 39.9
- Obese Class III: BMI >= 40.0

Asian Classification (WHO Western Pacific):
- Underweight: BMI < 18.5
- Normal weight: BMI 18.5 - 22.9
- Overweight (At Risk): BMI 23.0 - 24.9
- Obese Class I: BMI 25.0 - 29.9
- Obese Class II: BMI >= 30.0

Normal Weight Range Calculation:
Minimum Normal Weight = 18.5 x (Height in m)^2
Maximum Normal Weight = 22.9 x (Height in m)^2 [Asian] or 24.9 x (Height in m)^2 [WHO]

Example for 175 cm height:
Asian Normal Range: 18.5 x 3.0625 = 56.7 kg to 22.9 x 3.0625 = 70.1 kg
WHO Normal Range: 18.5 x 3.0625 = 56.7 kg to 24.9 x 3.0625 = 76.3 kg

Note: BMI uses the same formula regardless of age or sex for adults over 20. For children and teenagers, BMI percentiles adjusted for age and sex are used instead.

## Useful tips

BMI Is a Starting Point, Not the Full Picture: While BMI is a useful and convenient screening tool, it has well-known limitations. It does not distinguish between muscle mass and fat mass, does not account for body fat distribution, and does not consider factors like age, sex, ethnicity, or fitness level. A muscular athlete with low body fat may have a high BMI due to muscle weight, while an inactive person with high body fat but low muscle mass might have a misleadingly normal BMI. Use BMI as one data point alongside other health indicators.

Waist Circumference Is a Critical Complement: Health experts increasingly emphasize waist circumference as an important additional metric. Visceral fat (fat around internal organs in the abdominal area) is more strongly correlated with metabolic disease risk than overall body fat. For Korean adults, a waist circumference above 90 cm for men or 85 cm for women indicates increased metabolic risk, regardless of BMI. Measuring your waist at the navel level after a normal exhale provides this valuable data point.

Why Asian Standards Matter: Studies conducted across Asian populations have found that the risk of type 2 diabetes, hypertension, and cardiovascular disease begins to increase at lower BMI levels (around 23) compared to Western populations (around 25). This is attributed to differences in body composition — at the same BMI, Asian individuals tend to have a higher proportion of body fat and more visceral fat. If you are of Asian descent, the Asian BMI classification provides a more relevant health risk assessment.

BMI for Children and Teens: The standard BMI formula applies to adults aged 20 and above. For children and adolescents (ages 2-19), BMI must be interpreted using age-and-sex-specific percentile charts because body composition changes significantly during growth and development. A BMI-for-age at the 85th-95th percentile is considered overweight, and above the 95th percentile is considered obese.

Tracking Trends Over Time: Rather than fixating on a single BMI measurement, tracking your BMI over months and years provides more meaningful health insights. Gradual, unintentional weight gain or loss may indicate lifestyle changes, medical conditions, or medication side effects that warrant attention. Many health apps allow you to log weight over time and display BMI trends visually.

## FAQ

### Q. What is the BMI for 170cm and 70kg?

BMI = 70 / (1.70)^2 = 70 / 2.89 = 24.2. Under the WHO international standard, a BMI of 24.2 falls within the Normal weight range (18.5-24.9), very close to the upper boundary of normal. Under the Asian standard, however, this BMI of 24.2 is classified as Overweight (23.0-24.9), indicating that for individuals of Asian ethnicity, this weight level is associated with increased health risks. The normal weight range for 170cm height is 53.5-66.2 kg (Asian) or 53.5-71.9 kg (WHO). This example clearly illustrates why the choice of standard matters for health assessment.

### Q. Why are Asian and WHO standards different?

The WHO Western Pacific Regional Office established separate Asian-specific BMI thresholds based on extensive research showing that Asian populations experience increased risks of metabolic diseases (type 2 diabetes, hypertension, cardiovascular disease) at lower BMI levels compared to European populations. This is primarily because Asian individuals tend to have higher body fat percentages and more visceral (abdominal) fat at the same BMI. Studies in Korean, Japanese, Chinese, and South Asian populations consistently showed that health risks begin rising at BMI 23 rather than BMI 25. As a result, the Asian standard uses 23 as the overweight threshold and 25 as the obesity threshold, compared to the WHO international thresholds of 25 and 30 respectively.

### Q. How can I find my normal weight range?

This calculator automatically displays the normal weight range based on your height. The range is calculated by multiplying the square of your height in meters by the lower and upper BMI boundaries for normal weight. For Asian standards (BMI 18.5-22.9): minimum = 18.5 x height(m)^2, maximum = 22.9 x height(m)^2. For example, at 165 cm: minimum = 18.5 x 2.7225 = 50.4 kg, maximum = 22.9 x 2.7225 = 62.3 kg. For WHO standards (BMI 18.5-24.9): the maximum is higher at 24.9 x 2.7225 = 67.8 kg. Your target weight should ideally fall within this range, though individual factors like muscle mass and body composition should also be considered.

### Q. Is BMI accurate for athletes and very muscular people?

BMI has a well-known limitation for highly muscular individuals. Since BMI only considers total body weight relative to height, it cannot differentiate between muscle mass and fat mass. A bodybuilder or professional athlete with very low body fat but high muscle mass may have a BMI in the overweight or even obese range despite being in excellent health. For example, a 180 cm, 95 kg rugby player with 12% body fat would have a BMI of 29.3 (obese by Asian standards), which clearly misrepresents their health status. For such individuals, body fat percentage measurements (using DEXA scan, bioelectrical impedance, or skinfold calipers) provide a far more accurate assessment of body composition and health risk.

### Q. Does BMI change with age, and should older adults use different standards?

While the BMI formula itself does not change with age for adults, body composition does change naturally as people get older. After age 30-40, people tend to gradually lose muscle mass (sarcopenia) and gain fat mass, even if their weight and BMI remain stable. This means that an older adult with the same BMI as a younger adult likely has a higher body fat percentage. Some research suggests that slightly higher BMI ranges (around 23-27) may be associated with the lowest mortality risk in adults over 65, compared to the standard 18.5-24.9 range. However, no official age-adjusted BMI standards have been adopted. For older adults, maintaining muscle mass through regular exercise and adequate protein intake is as important as managing BMI.