Free BMI Calculator - Check Your Body Mass Index

Based on peer-reviewed medical formulas. See our formulas & sources ?

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Normal weight

What Is BMI?

A healthy BMI falls between 18.5 and 24.9. The Body Mass Index is calculated by dividing your weight in kilograms by your height in meters squared. A BMI below 18.5 indicates underweight, 25–29.9 indicates overweight, and 30 or above indicates obesity. BMI was developed by Adolphe Quetelet in the 1830s and is used worldwide by the World Health Organization as a screening tool for weight-related health risks.

Body Mass Index (BMI) is a simple screening tool that uses your weight and height to estimate body fat. Developed in the 1830s by Belgian mathematician Adolphe Quetelet, it is now widely used by the World Health Organization to assess population health. While BMI is not a diagnostic tool — it doesn't directly measure body fat or account for muscle mass — it serves as a useful starting point for identifying potential weight-related health risks.

Formula: BMI = weight (kg) ÷ height² (m²). Source: WHO, "Body mass index — BMI," 2000. Full methodology ?

How to Interpret Your BMI

Below 18.5

Underweight

18.5 – 24.9

Normal

25 – 29.9

Overweight

30 and above

Obese

These categories are defined by the World Health Organization. A BMI in the normal range is associated with the lowest risk of weight-related health conditions. However, BMI is just one measure — your overall health depends on many factors including diet, physical activity, and family history.

BMI Limitations

While BMI is a helpful screening tool, it has important limitations. It does not distinguish between muscle and fat, so muscular individuals may be misclassified as overweight. It also doesn't account for where fat is stored in the body, which matters — abdominal fat poses higher health risks than fat stored elsewhere. Additionally, BMI categories were developed primarily from Western populations and may not be equally accurate for people of different ethnicities, older adults, or pregnant women.

Healthy BMI Tips

Eat a balanced diet rich in fruits, vegetables, lean proteins, and whole grains while limiting processed foods and added sugars.
Stay physically active — aim for at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous activity per week.
Get enough sleep — poor sleep is linked to weight gain and higher BMI. Adults should aim for 7–9 hours per night.
Stay hydrated — drinking enough water supports metabolism and can help control appetite. Use our Water Intake Calculator to find your needs.

Frequently Asked Questions

What is a good BMI?

A BMI between 18.5 and 24.9 is considered normal and healthy. This range is associated with the lowest risk of weight-related health issues. Below 18.5 is underweight, 25-29.9 is overweight, and 30+ is obese.

How is BMI calculated?

BMI = weight (kg) ÷ height² (m²). For example, if you weigh 70 kg and are 1.75 m tall, your BMI is 70 ÷ (1.75 × 1.75) = 22.9, which is in the normal range.

Is BMI accurate for athletes?

BMI may overestimate body fat in athletes because it doesn't distinguish between muscle and fat. Muscular individuals often have a high BMI despite having very low body fat percentages.

What BMI is considered obese?

A BMI of 30 or higher is classified as obese. This is further divided into Class 1 (30-34.9), Class 2 (35-39.9), and Class 3 (40+, also called severe obesity).

Can BMI be wrong?

BMI doesn't distinguish between muscle and fat, doesn't account for where fat is stored, and may not be accurate for different ethnicities, older adults, pregnant women, or very tall or short individuals.

What is the healthy BMI range?

The WHO defines normal weight as BMI 18.5-24.9. However, some research suggests that for Asian populations, a lower range of 18.5-23 may be more appropriate due to differences in body composition.

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