How do you calculate BMI?

BMI is calculated by dividing body weight in kilograms by height in meters squared: BMI = Weight (kg) / Height (m)². For a person weighing 75 kg at 1.75 m tall: 75 / (1.75 × 1.75) = 24.5.

What is a normal BMI?

According to the WHO, a BMI between 18.5 and 24.9 is considered normal weight. Values below 18.5 indicate underweight, values from 25 indicate overweight, and from 30 indicate obesity.

How meaningful is BMI?

BMI is a simple screening value but has limitations: it doesn't distinguish between muscle and fat mass, doesn't account for fat distribution, and doesn't apply to children, pregnant women, or very muscular people. As an initial assessment, it's still useful.

Does BMI apply to children?

No, for children and adolescents under 18, age- and gender-specific BMI percentiles are used. A child with BMI 22 may be perfectly normal weight, while the same value at a different age may be classified differently.

What is the average BMI in Germany?

The average BMI in Germany is about 26.7 for men and 25.0 for women (Source: Federal Statistical Office / RKI DEGS1). This means the average falls in the overweight range.

At what BMI are you overweight?

According to the WHO, overweight starts at a BMI of 25.0 (pre-obese). From BMI 30 it's classified as Obesity Class I, from 35 Class II, and from 40 Class III (morbid obesity).

Does the ideal BMI change with age?

Yes, some experts recommend slightly higher BMI guidelines for older people. Studies show that a BMI of 25-27 in people over 65 is associated with the lowest mortality. However, WHO categories don't differentiate by age.

Why is BMI inaccurate for athletes?

Muscle mass is heavier than fat tissue. Muscular athletes can have a BMI over 25 despite low body fat percentage. Better metrics include body fat percentage (via calipers or DEXA scan) or the Ponderal Index.

What's the difference between BMI and body fat percentage?

BMI is based only on weight and height, while body fat percentage measures the actual fat proportion of total weight. Normal body fat is 10-20% for men and 20-30% for women. Body fat percentage is more meaningful but harder to measure.

How often should you calculate your BMI?

For healthy adults, calculating BMI every 6-12 months is sufficient. The trend over time is more important than the absolute value. During diet changes or training programs, monthly calculation can be useful.

Ideal Weight Calculation: 5 Methods Compared | BMI Calculator

What Is Ideal Weight?

Ideal weight is the body weight at which statistically the lowest health risks exist. It's not a fixed value but a range, depending on height, gender, age, body frame, and muscle mass.

Throughout history, various formulas have been developed to calculate ideal weight. Each has its strengths and weaknesses.

Method 1: BMI-Based

The most modern and widely used method derives ideal weight from BMI. Normal weight lies between BMI 18.5 and 25.0.

Formula:

\text{Ideal weight} = \text{BMI target} \cdot (\text{height in m})^2

Example at 1.75 m and BMI 22 (middle of normal range): 22 × 1.75² = 67.4 kg

Advantage: Internationally recognized, easy to calculate. Disadvantage: Doesn't consider gender, age, or body type.

Method 2: Broca Formula

The oldest and simplest formula, developed in 1871 by French physician Paul Broca.

Formula:

\text{Normal weight} = \text{height in cm} - 100

Ideal weight men: Normal weight − 10%

Ideal weight women: Normal weight − 15%

Example man, 180 cm: Normal weight = 80 kg, Ideal weight = 72 kg

Advantage: Very simple. Disadvantage: Inaccurate for very tall or short people, outdated.

Method 3: Creff Formula

A refinement of the Broca formula that considers age and body type.

Formula:

\text{Ideal weight} = \left(\text{height in cm} - 100 + \frac{\text{age}}{10}\right) \cdot 0.9 \cdot \text{body type factor}

Body type factors: Slim = 0.9, Normal = 1.0, Stocky = 1.1

Advantage: Considers more factors. Disadvantage: Body type is subjective.

Method 4: Hamwi Formula

Particularly widespread in the USA, developed in 1964.

Men: 48 kg for the first 152 cm + 2.7 kg per additional 2.5 cm

Women: 45 kg for the first 152 cm + 2.2 kg per additional 2.5 cm

Method 5: Waist-to-Height Ratio

The ratio of waist circumference to height. Target: below 0.5. When your waist circumference is less than half your height, your weight is optimal from a health perspective.

Which Method Is Best?

No single formula is perfect. The most meaningful approach is combining a BMI-based ideal weight range with waist circumference measurement. Ideal weight is always a range, not a fixed value.

Ideal Weight Calculation: 5 Methods Compared

What Is Ideal Weight?

Method 1: BMI-Based

Method 2: Broca Formula

Method 3: Creff Formula

Method 4: Hamwi Formula

Method 5: Waist-to-Height Ratio

Which Method Is Best?

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