How to Calculate BMI: Formula, Chart & Calculator

Body Mass Index (BMI) is one of the most widely used screening tools for assessing whether someone is at a healthy weight. While it's not a perfect measure, understanding your BMI is a useful starting point for conversations about health. This guide explains the BMI formula, shows you how to calculate it yourself, provides a reference chart, and discusses what BMI does and doesn't tell you.

What Is BMI?

BMI (Body Mass Index) is a numerical value calculated from your weight and height. It provides a simple way to categorize people into weight ranges — underweight, normal weight, overweight, and obese — without requiring any specialized equipment or tests.

BMI was developed in the 1830s by Belgian mathematician Adolphe Quetelet and has been used by healthcare professionals worldwide since the 1970s as a quick population-level screening tool.

The BMI Formula

There are two versions of the BMI formula depending on your measurement system:

Metric Formula

Imperial Formula

The multiplication factor of 703 in the imperial formula converts the units to match the metric-based BMI scale.

Step-by-Step Calculation Examples

Metric Example

Imperial Example

Don't want to do the math yourself? Use our free BMI Calculator — enter your height and weight and get your result instantly in either metric or imperial units.

BMI Categories Chart

Once you've calculated your BMI, here's how it's classified according to the World Health Organization (WHO):

BMI Reference by Height and Weight

Here's a quick-reference table showing BMI values for common height-weight combinations (imperial units):

What BMI Doesn't Tell You

While BMI is a useful screening tool, it has well-known limitations that are important to understand:

• Doesn't distinguish muscle from fat: Athletes and bodybuilders often have "overweight" or "obese" BMIs despite having low body fat percentages. Muscle is denser than fat.
• Doesn't account for fat distribution: Where you carry fat matters. Abdominal (visceral) fat is more dangerous than fat stored in the hips and thighs. BMI can't tell the difference.
• Varies by age and sex: Women naturally have more body fat than men at the same BMI. Older adults tend to have more body fat than younger adults at the same BMI.
• May not apply equally across ethnicities: Research suggests health risks associated with BMI levels may differ across ethnic groups. For example, Asian populations may face higher health risks at lower BMI levels.
• Not a diagnostic tool: BMI is a screening tool, not a diagnosis. A healthcare provider would use additional tests (body fat percentage, blood work, waist circumference) to assess overall health.

Healthy BMI Tips

If your BMI falls outside the normal range, here are evidence-based approaches to consider:

1. Focus on sustainable changes: Crash diets don't work long-term. Small, consistent changes to diet and activity level are more effective.
2. Combine diet and exercise: Both contribute to healthy weight management. Aim for at least 150 minutes of moderate activity per week.
3. Track your calories: Understanding your energy balance is key. Use our Calorie Calculator to find your daily energy needs.
4. Consult a professional: A doctor or registered dietitian can provide personalized guidance based on your full health picture.
5. Monitor over time: Regularly checking your BMI helps you track trends and catch changes early.

Calculate Your BMI Now

Ready to check your number? Our free BMI Calculator supports both metric and imperial units. Just enter your height and weight and you'll instantly see your BMI, its category, and what it means. It's a quick, private first step toward understanding your health profile.