Calculate your BMI instantly based on your age, gender, weight, and height. Learn how BMI relates to body fat percentage, get personalized health classification, and understand body composition based on WHO and CDC standards.
Calculate Your Body Mass Index & Understand Body Fat Percentage
BMI Formula:
BMI = Weight (kg) ÷ Height (m)² | First convert height from cm to meters by dividing by 100, then square the result, and divide weight by the squared height.Body Mass Index (BMI) is a widely used screening tool that estimates body fat based on height and weight. Developed in the 1830s by Belgian mathematician Adolphe Quetelet, BMI has become a standard health metric used by healthcare professionals worldwide.
BMI provides a simple, non-invasive method to categorize body weight relative to height. While it doesn't measure body fat directly, research shows strong correlations between BMI and body fat percentage for most adults. This makes it a valuable tool for population-level health assessments and individual screening.
BMI = Weight (kg) ÷ Height (m)²
Key Steps:
The World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) have established standard BMI categories for adults aged 18-65:
BMI Range: Less than 18.5
May indicate insufficient body weight, which could be associated with nutritional deficiencies, osteoporosis risk, or other health concerns. Consult a healthcare provider if you're consistently underweight.
BMI Range: 18.5 to 24.9
Generally associated with lower health risks for weight-related conditions. This range is often considered ideal for most adults, though individual health depends on many factors beyond BMI.
BMI Range: 25.0 to 29.9
May indicate excess body weight relative to height. Associated with increased risk for cardiovascular disease, type 2 diabetes, and other health conditions. Lifestyle modifications may be beneficial.
BMI Range: 30.0 and above
Indicates significantly excess body weight. Associated with substantially increased health risks including heart disease, stroke, type 2 diabetes, certain cancers, and reduced life expectancy. Professional medical guidance is recommended.
Important Note: BMI categories are general guidelines. Individual health assessment should include factors such as body composition, muscle mass, age, genetics, and overall fitness level. Always consult healthcare professionals for personalized health advice.
Let's calculate the BMI for a person who weighs 70 kg and is 175 cm tall:
Step 1: Identify your values
Step 2: Convert height to meters
Height in meters = 175 cm ÷ 100 = 1.75 m
Step 3: Square the height
Height² = 1.75 × 1.75 = 3.0625 m²
Step 4: Calculate BMI
BMI = Weight (kg) ÷ Height (m)²
BMI = 70 ÷ 3.0625
BMI = 22.86
Result: BMI = 22.86, which falls in the Normal weight category (18.5-24.9).
Our BMI calculator uses metric units (kg and cm), but here's how to convert from imperial units:
Formula:
Weight (kg) = Weight (lbs) ÷ 2.205
Example: 154 lbs ÷ 2.205 = 69.8 kg
Method 1: Convert to inches first
Example: 5'9" = (5 × 12) + 9 = 69 inches; 69 × 2.54 = 175.26 cm
Method 2: Direct conversion
Height (cm) = (Feet × 30.48) + (Inches × 2.54)
Example: 5'9" = (5 × 30.48) + (9 × 2.54) = 152.4 + 22.86 = 175.26 cm
Weight:
Height:
While BMI is a useful screening tool, it has important limitations that you should understand:
BMI calculates total body weight relative to height but doesn't differentiate between muscle mass and body fat. This means:
Two people with the same BMI can have very different body compositions:
Consider additional measurements if you:
Best Practice: Use BMI as one tool among many. Combine it with body composition analysis, waist measurements, fitness assessments, and regular health checkups for a complete health picture. Always consult healthcare professionals for personalized advice.
This calculator uses standard adult BMI categories (Underweight, Normal, Overweight, Obese) based on WHO guidelines. These categories apply to most adults aged 18-65.
BMI interpretation for children and teens requires age and gender-specific percentile charts, not adult categories. BMI-for-age percentiles account for:
CDC growth charts classify children as: Underweight (< 5th percentile), Healthy weight (5th-85th percentile), Overweight (85th-95th percentile), or Obese (≥ 95th percentile). Consult a pediatrician for accurate child BMI assessment.
Research suggests BMI ranges may differ for older adults:
Healthcare providers often use additional assessments alongside BMI for older adults.
BMI may not accurately reflect health status for athletes due to:
Body composition analysis (body fat percentage) provides more relevant information for athletes.
Some research suggests BMI thresholds may need adjustment for certain ethnic groups:
BMI categories are associated with different health risks and considerations:
Important: These associations are based on population-level research. Individual health depends on many factors including genetics, lifestyle, medical history, and body composition. BMI is a screening tool, not a diagnostic tool. Always consult healthcare professionals for personalized health guidance.
Understanding the relationship between BMI and body fat percentage is crucial for accurate health assessment. While both metrics relate to body composition, they measure different aspects:
BMI and body fat percentage are related but not interchangeable. Two people with the same BMI can have very different body fat percentages depending on muscle mass, age, and genetics.
Example: An athlete with BMI 26 (overweight range) might have 12% body fat percentage (healthy), while a sedentary person with the same BMI might have 28% body fat percentage (high).
While not as accurate as direct measurement, formulas can estimate body fat percentage using BMI, age, and gender:
Deurenberg Formula:
Body Fat % = (1.20 × BMI) + (0.23 × Age) - (10.8 × Gender) - 5.4
Where Gender = 1 for male, 0 for female
Note: This formula has limitations and may not be accurate for athletes or individuals with unusual body compositions.
Unlike BMI categories, body fat percentage ranges vary by gender and age:
Best Practice: For most people, BMI provides a good starting point. If you need more detailed body composition analysis, especially if you're an athlete or have specific fitness goals, consider measuring body fat percentage using professional methods like DEXA scans or bioelectrical impedance analysis.
BMI can be a useful tool for tracking progress in weight management programs:
Remember:
For effective weight management, consider working with:
Adult Male (30 years): 70 kg weight, 175 cm height
Result: BMI = 22.9 (Normal weight) - Standard adult BMI category applies.
Adult Female (35 years): 90 kg weight, 180 cm height
Result: BMI = 27.8 (Overweight) - Note: Body composition may differ between men and women.
Adult Female (25 years): 55 kg weight, 160 cm height
Result: BMI = 21.5 (Normal weight) - Healthy range for adult women.
Adult Male (40 years): 100 kg weight, 170 cm height
Result: BMI = 34.6 (Obese) - Consult healthcare provider for weight management guidance.
Teen Female (16 years): 50 kg weight, 170 cm height
Result: BMI = 17.3 (Underweight - see note) - BMI-for-age percentile charts should be used for accurate assessment.
Senior Male (70 years): 80 kg weight, 180 cm height
Result: BMI = 24.7 (Normal weight) - For adults 65+, BMI 24-27 may be associated with better outcomes.
BMI (Body Mass Index) is a measure of body fat based on height and weight. The formula is BMI = Weight (kg) ÷ Height (m)². For example, a person weighing 70 kg and 175 cm tall has a BMI of 70 ÷ (1.75)² = 22.9. BMI provides a simple numerical measure of body weight relative to height.
BMI categories for adults (18-65 years) are: Underweight (BMI < 18.5), Normal weight (BMI 18.5-24.9), Overweight (BMI 25-29.9), and Obese (BMI ≥ 30). These categories are based on World Health Organization (WHO) and CDC guidelines.
BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat, so athletes with high muscle mass may have higher BMI despite being fit. BMI also doesn't account for age, gender, bone density, or body composition. It's best used as a general indicator alongside other health metrics.
A healthy BMI range for adults is typically 18.5 to 24.9, classified as "Normal weight." However, individual health depends on many factors beyond BMI, including muscle mass, body composition, age, and overall fitness. Consult with a healthcare professional for personalized guidance.
Divide your weight in pounds by 2.205 to get kilograms. For example, 154 pounds ÷ 2.205 = 69.8 kg. You can also multiply pounds by 0.4536 for the same result.
First convert to total inches (feet × 12 + inches), then multiply by 2.54 to get centimeters. For example, 5 feet 9 inches = (5 × 12) + 9 = 69 inches; 69 × 2.54 = 175.26 cm. Alternatively: multiply feet by 30.48 and add inches × 2.54.
BMI calculations for children and teens (ages 2-20) require age and gender-specific percentile charts, not the adult BMI categories. BMI-for-age percentiles are used instead. This calculator is designed for adults aged 18-65. Consult a pediatrician for child BMI assessments.
The same BMI formula applies to both men and women, but the interpretation may vary slightly. Men typically have more muscle mass than women at the same BMI, which can affect health implications. However, the BMI categories (underweight, normal, overweight, obese) are the same for both genders according to WHO standards.
If your BMI indicates overweight or obesity, consult with a healthcare professional for personalized advice. They can help create a safe and effective plan that may include dietary changes, increased physical activity, and lifestyle modifications. Focus on sustainable, long-term changes rather than quick fixes.
There's no strict frequency requirement, but checking monthly or quarterly can help track progress if you're working toward weight management goals. Remember that BMI is just one indicator; focus on overall health, energy levels, and how you feel rather than BMI alone.
No, BMI does not distinguish between muscle and fat mass. Athletes, bodybuilders, and individuals with high muscle mass may have a BMI in the overweight or obese range despite having low body fat. In such cases, body composition analysis (body fat percentage) provides more accurate health assessment.
BMI estimates body fat indirectly through height and weight, while body fat percentage directly measures the proportion of fat in your body. Body fat percentage (measured via DEXA scan, bioelectrical impedance, or other methods) provides more detailed information about body composition but requires specialized equipment.
While BMI cannot directly calculate body fat percentage, there are formulas that estimate body fat percentage using BMI, age, and gender. The Deurenberg formula is one example: Body Fat % = (1.20 × BMI) + (0.23 × Age) - (10.8 × Gender) - 5.4, where Gender is 1 for male and 0 for female. However, these estimates have limitations and may not be accurate for athletes or individuals with unusual body compositions.
Healthy body fat percentage ranges vary by age and gender. For men: 10-20% is considered healthy, 21-25% is acceptable, and above 25% is considered high. For women: 18-28% is considered healthy, 29-35% is acceptable, and above 35% is considered high. These ranges differ from BMI categories because body fat percentage directly measures fat mass.
BMI provides a rough estimate of body fat percentage for the general population, but it's not precise. Two people with the same BMI can have very different body fat percentages depending on muscle mass, age, and genetics. For accurate body fat percentage measurement, use methods like DEXA scans, bioelectrical impedance analysis, or hydrostatic weighing.
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