BMI Calculator

What Is BMI?

Body Mass Index (BMI) is a widely used screening tool that compares your weight to your height. Doctors, nurses, and health professionals around the world use it as a quick first check for weight-related health risks. This tool gives you your result instantly, along with a clear explanation of what it means.

Whether you are tracking your health, preparing for a medical appointment, or simply curious — this page provides the information you need in seconds.

How the Calculation Works

We use the standard World Health Organization formula:

For example, a person who is 175 cm tall and weighs 75 kg has a BMI of 75 ÷ (1.75 × 1.75) = 24.5. According to the WHO scale, this falls in the Normal weight range. This page also supports imperial units — enter your height in feet and inches and weight in pounds, and the tool converts automatically.

How to Use This Tool

1. Select your unit system — metric (cm and kg) or imperial (feet, inches, and pounds).
2. Enter your height — use your actual height, not an estimate.
3. Enter your weight — use your current weight for an accurate result.
4. Click Calculate — your score, category, and healthy weight range appear instantly.

Understanding Your Result

Your score falls into one of four main categories. Here is what each one means:

• Under 18.5 — Underweight: Your weight may be too low for your height. This can indicate nutritional deficiency or other health issues. Consult a doctor.
• 18.5 to 24.9 — Normal weight: This is the healthy range according to the WHO. A result in this range is associated with the lowest risk of weight-related health conditions.
• 25 to 29.9 — Overweight: Your weight is above the healthy range for your height. This is associated with elevated risk of type 2 diabetes, heart disease, and other conditions.
• 30 and above — Obese: Significantly elevated health risk. Medical advice is recommended. Obesity is further divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+).

Is This Accurate?

The calculation is accurate as a population screening tool. However, it has important limitations at the individual level. It does not distinguish between muscle and fat — therefore, a muscular athlete may score as overweight despite having very low body fat. Furthermore, it does not account for age, sex, or ethnicity differences in body composition.

According to the World Health Organization (WHO), BMI is a useful population-level measure but should be supplemented with other assessments for individual clinical decisions. Use this as a starting point, then consult a healthcare professional for a complete picture.

Gender Differences

For Women

The same formula applies to both men and women. However, women naturally carry more body fat than men at the same score. This is because women have a higher proportion of subcutaneous fat and lower average muscle mass — both of which are biologically normal.

Therefore, a woman at the upper end of the normal range may have a higher body fat percentage than a man at the same score. For a more detailed body composition assessment, use our Body Fat Calculator alongside this tool.

For Men

For men, this works well as a general screening tool. However, men who do significant strength training often score in the overweight range despite having low body fat — because muscle is denser than fat and adds weight without adding health risk.

In contrast, some men have a normal result but carry excessive visceral fat around the abdomen — which is actually more health-threatening than subcutaneous fat. Waist circumference measurement alongside this tool gives a more complete picture for men.

Common Mistakes to Avoid

• Using inaccurate measurements: The result is only as accurate as the height and weight you enter. Use a scale and measuring tape rather than estimates.
• Treating it as a definitive diagnosis: This is a screening tool. It does not diagnose any condition. A healthcare professional uses it alongside blood tests, waist measurement, and other indicators for a complete assessment.
• Applying adult ranges to children: Children’s BMI uses age and sex-adjusted percentile charts. Never use an adult tool for anyone under 18.

Alternative Measures

BMI is not the only way to assess body composition. Here are other useful metrics:

• Body Fat Percentage — measures actual fat mass vs. lean mass. More accurate for athletes. Try our Body Fat Calculator.
• Waist-to-Hip Ratio — indicates abdominal fat distribution and cardiovascular risk.
• Waist-to-Height Ratio — a simple screening tool: your waist should be less than half your height.
• Ponderal Index — similar to BMI but uses height cubed instead of squared. Better for very tall or short individuals.

Frequently Asked Questions