BMI Calculator - Body Mass Index With WHO Categories

A single number that changes your next doctor's visit

Body Mass Index divides your weight in kilograms by your height in meters squared. The result lands on a scale defined by the World Health Organization - from severe thinness below 16.0 through normal weight (18.5 - 24.9) to class III obesity above 40.0. This calculator runs the formula, classifies the result, and shows exactly how many kilograms separate you from the healthy range.

How to calculate BMI - step by step

Weight - enter your body weight in kilograms. Morning measurement on an empty stomach gives the most consistent reading.
Height - enter your height in centimeters, measured barefoot.
Sex - select female or male. The BMI formula is the same for both, but body fat distribution differs.
Age (optional) - adding your age provides better context. For children under 18, BMI percentile charts are more appropriate.
Read the results - the calculator shows your BMI value, WHO category, healthy weight range and the gap to that range.

WHO BMI classification table

The World Health Organization defines these BMI categories for adults aged 20 and older:

Category	BMI range	Health risk
Severe thinness	< 16.0	Very high
Moderate thinness	16.0 - 16.9	High
Underweight	17.0 - 18.4	Moderate
Normal weight	18.5 - 24.9	Low
Overweight	25.0 - 29.9	Increased
Obesity class I	30.0 - 34.9	High
Obesity class II	35.0 - 39.9	Very high
Obesity class III	≥ 40.0	Extremely high

Healthy weight range by height

BMI between 18.5 and 24.9 corresponds to these weight ranges:

Height	Min weight (BMI 18.5)	Max weight (BMI 24.9)
155 cm	44.4 kg	59.8 kg
160 cm	47.4 kg	63.7 kg
165 cm	50.4 kg	67.8 kg
170 cm	53.5 kg	71.9 kg
175 cm	56.7 kg	76.3 kg
180 cm	59.9 kg	80.7 kg
185 cm	63.3 kg	85.2 kg
190 cm	66.8 kg	89.9 kg

Practical examples

Example 1: Female, 165 cm, 58 kg. BMI = 58 / 1.65^2 = 21.3 - Normal weight. Healthy range: 50.4 - 67.8 kg. No gap.

Example 2: Male, 180 cm, 95 kg. BMI = 95 / 1.80^2 = 29.3 - Overweight. 14.3 kg above the healthy max of 80.7 kg.

Example 3: Female, 170 cm, 50 kg. BMI = 50 / 1.70^2 = 17.3 - Underweight. 3.5 kg below the healthy min of 53.5 kg.

Example 4: Male, 175 cm, 110 kg. BMI = 110 / 1.75^2 = 35.9 - Obesity class II. 33.7 kg above healthy max.

Example 5: Male, 190 cm, 82 kg. BMI = 82 / 1.90^2 = 22.7 - Normal weight. Right in the middle of the healthy range (66.8 - 89.9 kg).

FAQ - Frequently asked questions

What is the BMI formula?

BMI = weight (kg) / height (m)^2. A person weighing 75 kg at 1.78 m has a BMI of 75 / 3.1684 = 23.7.

Does BMI work for athletes?

BMI does not distinguish between muscle and fat. A muscular athlete at 180 cm and 95 kg shows BMI 29.3 (overweight), even though body fat may be low. For athletes, body fat percentage or waist-to-hip ratio (WHR) is more accurate.

Is BMI the same for men and women?

The formula and category thresholds are identical. However, women naturally carry more body fat (roughly 20-25% vs 15-20% for men at normal BMI), so the same BMI value may represent different health profiles.

What BMI is considered healthy?

The WHO defines normal weight as BMI between 18.5 and 24.9. Below 18.5 is underweight, above 25.0 is overweight. The lowest statistical risk of chronic disease falls between BMI 20 and 22.

Can I use BMI for children?

No. Children's BMI must be compared against age-and-sex-specific growth charts (percentiles). A BMI of 22 can be overweight for a 6-year-old but normal for a 16-year-old. Use a child BMI percentile calculator instead.

What does the "gap to healthy range" mean?

If your BMI is below 18.5, the gap shows how many kilograms you need to gain to reach the lower boundary of normal weight. If above 24.9, it shows how many kilograms separate you from the upper boundary. At normal weight, the gap is 0.

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