BMI Calculator

Enter your height and weight in metric or US units to get your body mass index (BMI) and the standard adult weight category. BMI is a quick screening number, not a diagnosis.

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kg
Enter your height and weight, then press Calculate BMI.

The BMI formula

Body mass index compares weight to height. In metric units it is weight in kilograms divided by height in metres squared:

BMI = weight(kg) ÷ height(m)2

In US units, multiply by a conversion factor of 703:

BMI = 703 × weight(lb) ÷ height(in)2

Worked example

Someone 175 cm tall weighing 70 kg:

Height in metres: 175 ÷ 100 = 1.75 m.
Squared: 1.75 × 1.75 = 3.0625.
BMI: 70 ÷ 3.0625 ≈ 22.9 — in the healthy range.

Standard adult BMI categories

BMICategory
Below 18.5Underweight
18.5 – 24.9Healthy weight
25.0 – 29.9Overweight
30.0 and aboveObesity
Note: BMI is a population screening tool. It doesn't distinguish muscle from fat, so very muscular people can read high while it underestimates body fat in some others. It is for adults 20+; children use age-and-sex percentiles.

Frequently asked questions

How is BMI calculated?

BMI is weight in kilograms divided by height in metres squared (kg/m²). In US units it is 703 × pounds ÷ inches². The same number results either way.

What is a healthy BMI?

For adults, 18.5 to 24.9 is the healthy range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or more is in the obesity range, per CDC cut-offs.

Is BMI accurate for athletes?

Not always. BMI doesn't separate muscle from fat, so muscular athletes can register as overweight despite low body fat. Use it as one screening signal alongside waist size and other measures.

Does BMI work for children?

No — children and teens use age- and sex-specific BMI-for-age percentiles, not the fixed adult categories. This calculator is intended for adults 20 and older.

MB
Mustafa Bilgic · Editor, Calcool
The BMI formula and adult weight categories follow the U.S. Centers for Disease Control and Prevention (CDC). BMI is a screening tool, not a diagnosis; consult a healthcare professional about your individual health.

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