⚖️ BMI Calculator

Calculate your Body Mass Index (BMI) to understand your current weight status and identify your healthy weight range. Provides WHO BMI classification along with BMI Prime, Ponderal Index, and other health indicators.

Age (years)

Gender

Height (cm)

Weight (kg)

BMI (Body Mass Index)

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BMI Category — BMI Prime — Ponderal Index (PI) — Healthy Weight Range —

GUIDE

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What is BMI?

BMI (Body Mass Index) is an obesity measurement indicator calculated from the ratio of height to weight. Developed by Belgian mathematician Adolphe Quetelet in 1832, it is the most widely used weight assessment tool worldwide.

BMI Calculation Formula

BMI = weight(kg) ÷ (height(m))². Example: Weight 70kg, Height 175cm → BMI = 70 ÷ (1.75)² = 22.86. The WHO classifies underweight (below 18.5), normal (18.5-24.9), overweight (25-29.9), and obese (30 and above).

WHO BMI Classification

Category	BMI Range	Health Risk
Severe Thinness	< 16	High
Moderate Thinness	16 - 16.9	Moderate
Mild Thinness	17 - 18.4	Low
Normal	18.5 - 24.9	Minimal
Overweight	25 - 29.9	Low
Obese Class I	30 - 34.9	Moderate
Obese Class II	35 - 39.9	High
Obese Class III	≥ 40	Very High

Health Risks of Overweight/Obesity

Being overweight or obese increases the risk of the following health problems: Type 2 diabetes, high blood pressure and cardiovascular disease, stroke, certain cancers (colon, breast, uterine, etc.), osteoarthritis, sleep apnea, and fatty liver disease.

Health Risks of Being Underweight

Being underweight can also cause the following health problems: malnutrition and weakened immune system, osteoporosis, anemia, reproductive dysfunction, and growth and development delays (in adolescents).

Limitations of BMI

While BMI is a useful indicator, it does not distinguish between muscle mass and fat mass, athletes or muscular individuals may be classified as overweight, it does not adequately account for differences in age, gender, and ethnicity, and it does not consider fat distribution such as abdominal obesity. Therefore, BMI should be evaluated comprehensively with other indicators such as body fat percentage and waist circumference.

What is BMI Prime?

BMI Prime is your actual BMI divided by 25 (the overweight threshold). A value of 1.0 or higher indicates overweight, while below 1.0 indicates normal or underweight. For example, a BMI Prime of 1.2 means you are 20% heavier than normal weight.

What is Ponderal Index?

Ponderal Index (PI) is similar to BMI but uses the cube of height in its calculation. PI provides a more accurate indicator for tall and short individuals. The normal range is approximately 12-13.

When to See a Doctor

Professional consultation is recommended when your BMI is 30 or higher, when your BMI is below 18.5, with rapid weight changes in a short period, with obesity-related health problems (diabetes, high blood pressure, etc.), or when you have difficulty managing weight.

Frequently asked questions

How is BMI calculated?

BMI = weight(kg) ÷ height(m)². For example, weight 70kg and height 175cm gives 70 ÷ (1.75)² = 22.86.

What is the normal BMI range?

The WHO normal range is 18.5-24.9. For Asians including Koreans, 18.5-22.9 is recommended due to body type characteristics.

Can I be unhealthy with a normal BMI?

Yes. BMI does not distinguish muscle mass from fat mass, so "skinny fat" individuals with low muscle and high body fat can have a normal BMI but elevated metabolic disease risk.