Obesity Level Calculation — From the BMI Formula to Normal Ranges and Overweight Criteria

When I bring up weight in the consultation room, the first question I hear is, "Doctor, am I obese?" I would have asked the same thing. Just looking at the number on the scale, it's hard to get a sense of where my body stands. That's why we need an obesity calculation tool commonly used by health centers and hospitals. With just two numbers—height and weight—it objectively pinpoints my position, making it the perfect first step for a diet. Today, I'll explain how the most widely used Body Mass Index (BMI) formula is calculated and interpreted, and even the areas this number cannot reach, with the explanations I often give in the consultation room.

![Box-type formula visualization emphasizing the BMI calculation formula. The formula is highlighted with double underlines, and the units for each variable (kg, m) are clearly marked. Designed to instill trust by using a formula style found in some hospital and health center charts]](/api/files/assets/2026-06/1b5a733d.png?sig=6336adb2290ee7b9ef05e7cdc1ffe3909b749c8a6a8c0fb6c951c849d087a558)

The number called BMI, exactly how is it created?

Obesity level is usually calculated by Body Mass Index (BMI). The formula is simple.

BMI = Weight(kg) ÷ [Height(m)]²

Since weight is divided by the square of the height, the denominator grows rapidly as height increases. This is why BMI varies greatly depending on height, even for the same 70kg. This formula is commonly used by public health centers, local governments, and hospitals nationwide, such as in Imsil-gun, Seongnam-si, Jinju-si, Ulsan Nam-gu, and Hanam-si. The important point is that it is standardized so that anyone, anywhere, gets the same number. For those who come to receive diet herbal medicine, writing this number at the front of the medical chart makes tracking changes much easier.

![Visualization of a 3-step flowchart using an example of 170cm, 70kg. First: Convert 170cm to 1.70m / Second: Calculate 1.70×1.70=2.89 / Third: 70÷2.89=24.2]](/api/files/assets/2026-06/9cd7c264.png?sig=b4d978c69897340183c9283e660a2b38b0411402e615d0d50c00da5cbc859b68)

Let's try calculating with actual numbers

Since it might feel difficult just hearing it in words, let's look at an example together. Suppose someone is 170cm tall and weighs 70kg.

• Convert height to meters. 170cm → 1.70m
• Find the square of the height. 1.70 × 1.70 = 2.89
• Divide weight by that value. 70 ÷ 2.89 ≒ 24.2 kg/m²

This person's BMI is approximately 24.2. You don't even need to tap a calculator; a phone memo is enough. When I calculate it directly for patients in the consultation room, many react, "Oh, it's higher than I thought." Seeing just the number 70 on the scale feels different from seeing it converted to a BMI of 24.2. Even at the same 70kg, a person who is 180cm tall falls into the 21 range, right in the middle of the normal range. This is why it's not just a simple weight comparison; it only makes sense when viewed together with height.

![Comparison table representing the 6-level BMI classification system. Each category from underweight to Class 3 obesity is listed as a row, with the BMI numerical range and classification name clearly marked. The 24.2 example is marked as 'Pre-obesity (Overweight)']](/api/files/assets/2026-06/6c960fc3.png?sig=a24e1416d2665196c45f6286c7d7046aacf65b93d1abe6655047f2b6bee25a6f)

Where does 24.2 belong — Looking at the normal range

Domestic public health center criteria, which follow the standards of the Korean Society for the Study of Obesity and the Korea Disease Control and Prevention Agency, are divided as follows:

• Underweight: BMI under 18.5
• Normal weight: BMI 18.5 ~ 22.9
• Pre-obesity (Overweight): BMI 23.0 ~ 24.9
• Stage 1 Obesity: BMI 25.0 ~ 29.9
• Stage 2 Obesity: BMI 30.0 ~ 34.9
• Stage 3 (Severe) Obesity: BMI 35.0 or above

The 24.2 calculated previously falls under Pre-obesity (Overweight). It is not yet obesity, but it is a section standing on the boundary between normal and obesity. In the consultation room, I tell those in this section, "Now is the best place to turn things around." Once you move to Stage 1 obesity (25.0~29.9), the difficulty of weight loss increases by one level.

For reference, some health centers also look at the obesity level (%) relative to standard weight. The formula is {(current weight − standard weight) ÷ standard weight} × 100, and if it is +10% or less relative to standard weight, it is judged as normal. For an accurate assessment, please also refer to the guidance from your health center or hospital.

There are people for whom this formula does not fit

BMI is not a universal solution. Since it is a formula that only looks at height and weight, it cannot distinguish body composition. There are representative cases where it does not fit:

• People with high muscle mass — Bodybuilders or those who have been working out for a long time have heavy muscle, so even if BMI shows obesity, they are actually healthy
• The elderly — If muscle decreases and fat increases but weight is similar, BMI shows normal. Even though the actual body composition is not like that
• Pregnant women — Because fetal and amniotic fluid weight is added, BMI interpretation is meaningless

In such cases, it is difficult to conclude obesity status based on a single BMI number. In the consultation room, quite a few people come with "normal BMI but only a protruding belly." If you trust only BMI and feel reassured, it's easy to miss abdominal fat. So, you need to look at supplementary indicators together.

![A checklist expressing supplementary indicators to check alongside BMI. Checkboxes (✅) are placed in front of each indicator (body fat percentage, muscle mass, waist circumference, blood pressure, blood sugar, cholesterol) to visualize the practical judgment flow.]](/api/files/assets/2026-06/37aebf0c.png?sig=e09d27864b6b176d4cd4a39dbf7d87cd684daaa00e6e122a1f74dfed4236220b)

Supplementary Indicators to Check Alongside BMI

Don't end with just the number on the scale—here are the indicators you can check alongside it that make the picture much clearer.

• Body fat percentage — Checked with body composition measuring devices like InBody. Even if BMI is normal, if body fat percentage is high, it's skinny-fat obesity.
• Muscle mass (skeletal muscle mass) — Even at the same weight, if muscle supports you, basal metabolic rate is maintained. When dieting, if muscle is lost too, yo-yo effect is bound to come.
• Waist circumference — An indicator of abdominal obesity. If BMI is normal but waist circumference increases, you should suspect visceral fat.
• Blood pressure, blood sugar, cholesterol — Even at the same BMI, metabolic health can differ, so look at them together.

For those who come to receive diet herbal medicine, we also measure BMI, body composition, and waist circumference together at the first visit. Don't cling to a single number; look at it from multiple angles to set the diet direction. Rather than weighing yourself on a 1-day basis and being elated or dejected, it's much more helpful to examine body composition trends weekly.

![Large text emphasizing the key closing message from the blog. A realistic sentence drawn from clinic experience, contrasting the meaning of numbers with the direction of real change.]](/api/files/assets/2026-06/f4455270.png?sig=c9da546b745c2c4eac25fc560b32e8bc6c9a4a6d4fe1cb29f96a4d75c51b6527)

One line from the Korean Medicine perspective

In Korean Medicine, even with the same BMI, if the constitution patterns such as Qi deficiency, dampness-phlegm, or blood stasis differ, the location where fat accumulates and the speed at which it is lost are also considered different.

The obesity calculation we covered today is the first step of a diet. There's no need to be discouraged if you got 24.2, and no need to be complacent if you got 22. Numbers are just the starting line; real change begins by examining what pattern your body gained fat in. At Baekrokdam Korean Medicine Clinic, we measure BMI, body composition, and waist circumference together, and help you find a way to lose weight without strain through a Baekrok Gambi-jung tablet prescription tailored to your constitution. If you've been feeling dizzy alone in front of the scale, let's organize the numbers together in the consultation room.