Our free online BMI (Body Mass Index) calculator helps you quickly determine your BMI and understand what it means for your health. Simply enter your weight in kilograms and height in centimeters, and the calculator will instantly compute your BMI and classify it into one of four categories: Underweight, Normal, Overweight, or Obese. This tool is perfect for health monitoring, fitness tracking, and understanding your body composition.
Using our BMI calculator is straightforward. Enter your weight in kilograms in the first field and your height in centimeters in the second field. The calculator will automatically compute your BMI and display both the numerical value and the corresponding category. The calculation updates in real-time as you type, providing instant results without needing to click any buttons. The BMI is displayed as a single decimal number for precision.
Body Mass Index (BMI) is a numerical value derived from your weight and height. It's calculated by dividing your weight in kilograms by the square of your height in meters. The formula is: BMI = weight (kg) / [height (m)]². BMI is used as a screening tool to identify whether a person is underweight, at a healthy weight, overweight, or obese. While BMI doesn't directly measure body fat, research has shown that it correlates with direct measures of body fat and can be an effective indicator of health risks.
The World Health Organization (WHO) classifies BMI into the following categories for adults:
Underweight (BMI less than 18.5): Indicates that you may be underweight, which can be associated with health issues such as weakened immune system, nutritional deficiencies, osteoporosis, and decreased muscle strength. Being underweight can result from various factors including insufficient calorie intake, high metabolism, or underlying health conditions.
Normal Weight (BMI 18.5 - 24.9): Suggests a healthy weight range for your height. This range is associated with the lowest health risks and is considered optimal for most adults. Maintaining a BMI in this range can reduce the risk of developing weight-related health conditions.
Overweight (BMI 25 - 29.9): Indicates that you may be above the healthy weight range for your height. Being overweight increases the risk of developing health problems such as heart disease, high blood pressure, type 2 diabetes, and certain types of cancer. However, BMI alone doesn't account for muscle mass or body composition.
Obese (BMI 30 or greater): Suggests significant excess body weight that substantially increases health risks. Obesity is associated with numerous serious health conditions including cardiovascular disease, diabetes, sleep apnea, joint problems, and reduced life expectancy. It's important to consult healthcare professionals for proper assessment and management.
The BMI formula is simple but requires proper unit conversion:
Metric Formula: BMI = weight (kg) / [height (m)]²
Example: A person weighing 70 kg and 170 cm tall:
Height in meters = 170 cm ÷ 100 = 1.7 m
BMI = 70 ÷ (1.7 × 1.7) = 70 ÷ 2.89 = 24.2
This person's BMI is 24.2, which falls in the Normal range.
Imperial Formula: BMI = [weight (lbs) / height (inches)²] × 703
Example: A person weighing 154 lbs and 67 inches tall:
BMI = (154 ÷ (67 × 67)) × 703 = (154 ÷ 4,489) × 703 = 24.2
This person's BMI is 24.2, which is Normal.
Example 1 - Underweight:
Weight: 50 kg, Height: 175 cm (1.75 m)
BMI = 50 ÷ (1.75 × 1.75) = 16.3
Category: Underweight
Example 2 - Normal:
Weight: 68 kg, Height: 168 cm (1.68 m)
BMI = 68 ÷ (1.68 × 1.68) = 24.1
Category: Normal
Example 3 - Overweight:
Weight: 82 kg, Height: 165 cm (1.65 m)
BMI = 82 ÷ (1.65 × 1.65) = 30.1
Category: Obese
While BMI is a useful screening tool, it has important limitations:
Doesn't Distinguish Muscle from Fat: BMI doesn't differentiate between muscle and fat mass. Athletes and bodybuilders with high muscle mass may have high BMIs but low body fat percentages.
Doesn't Account for Body Composition: Two people with the same BMI can have very different body compositions, with one having more muscle and the other having more fat.
Age and Gender Differences: BMI doesn't account for age or gender differences in body composition. Older adults and women naturally have higher body fat percentages than younger people and men at the same BMI.
Ethnicity Variations: Different ethnic groups have different health risk profiles at the same BMI levels. For example, Asian populations may have higher health risks at lower BMIs.
Not Suitable for Everyone: BMI is not appropriate for pregnant women, children, elderly individuals, or those with certain medical conditions. These groups require specialized assessment methods.
Your BMI can provide important insights into potential health risks:
Cardiovascular Health: Higher BMI is associated with increased risk of heart disease, high blood pressure, and stroke. Maintaining a healthy BMI reduces cardiovascular risk factors.
Diabetes Risk: Obesity significantly increases the risk of developing type 2 diabetes. Weight loss in overweight individuals can improve insulin sensitivity and reduce diabetes risk.
Joint Health: Excess weight puts additional stress on joints, particularly knees, hips, and lower back, leading to osteoarthritis and chronic pain.
Cancer Risk: Higher BMI is associated with increased risk of certain cancers including breast, colon, kidney, and pancreatic cancer.
Mental Health: Both very low and very high BMI can be associated with mental health challenges, including depression, anxiety, and eating disorders.
Reproductive Health: BMI affects fertility in both men and women. Being significantly underweight or overweight can impact hormone levels and reproductive function.
Balanced Diet: Focus on whole foods, fruits, vegetables, lean proteins, and whole grains. Avoid processed foods high in sugar and unhealthy fats.
Regular Exercise: Aim for at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous activity per week, plus strength training twice weekly.
Portion Control: Be mindful of serving sizes. Use smaller plates, measure portions, and avoid eating directly from packages.
Stay Hydrated: Drink adequate water throughout the day. Sometimes thirst is mistaken for hunger.
Quality Sleep: Get 7-9 hours of sleep per night. Poor sleep disrupts hormones that regulate appetite and metabolism.
Stress Management: Chronic stress can lead to emotional eating and weight gain. Practice stress-reduction techniques like meditation, yoga, or deep breathing.
Professional Guidance: Consult healthcare providers, registered dietitians, or certified fitness professionals for personalized advice and support.
While our BMI calculator provides useful information, it's important to consult healthcare professionals if:
• Your BMI falls outside the normal range (below 18.5 or above 25)
• You're experiencing unexplained weight changes
• You have concerns about your weight or health
• You're planning significant lifestyle changes
• You have existing health conditions affected by weight
• You need personalized dietary or exercise recommendations
For a more comprehensive health assessment, consider these additional measurements:
Waist Circumference: Measures abdominal fat, which is linked to higher health risks. Men should aim for less than 40 inches (102 cm), women less than 35 inches (88 cm).
Waist-to-Hip Ratio: Divides waist measurement by hip measurement to assess fat distribution. Values above 0.90 for men and 0.85 for women indicate higher risk.
Body Fat Percentage: Direct measurement of fat versus lean mass using methods like bioelectrical impedance, DEXA scans, or skinfold calipers.
Waist-to-Height Ratio: Your waist should be less than half your height. This simple measure can indicate health risks.
Your privacy is our priority. All BMI calculations are performed locally in your web browser using JavaScript. We don't store, transmit, or save any of your weight or height information on our servers. The calculator works entirely offline once the page is loaded, ensuring your personal health data remains completely private and secure. No information is collected, tracked, or shared with any third parties.