BMI Calculator
Calculate your Body Mass Index (BMI), ideal weight, body fat percentage, and Basal Metabolic Rate (BMR). Supports both metric and imperial units with gender-specific calculations.
- Free, no sign-up
- REST + MCP
- Updated
- Reviewed by Olgun Ozoktas
Enter your details to calculate BMI and other metrics
BMI Categories
Underweight0 - 18.5
Normal18.5 - 25
Overweight25 - 30
Obese Class I30 - 35
Obese Class II35 - 40
Obese Class III40 - 40+
These calculations are estimates and may not be accurate for athletes, elderly, pregnant women, or individuals with certain health conditions. Always consult a healthcare professional for personalized advice.
How to Calculate Your BMI Online
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Select your unit system
Choose between Metric (kilograms and centimeters) or Imperial (pounds, feet, and inches). The calculator adapts all input fields and results to your preferred measurement system. -
Enter your personal details
Provide your gender, age, weight, and height. Gender and age are used for body fat estimation and BMR calculations, while weight and height determine your BMI score. -
Review your BMI results
Your BMI score appears instantly along with your WHO weight category (underweight, normal, overweight, or obese). The healthy weight range for your specific height is also displayed. -
Explore additional health metrics
Scroll down to see your ideal weight across four medical formulas, estimated body fat percentage with category ranges, and your Basal Metabolic Rate calculated using three established methods.
Common Use Cases
Routine Health Checkups
Track your BMI between doctor visits to monitor weight changes and stay within a healthy range. Many healthcare providers use BMI as a first-pass screening tool during annual physicals.
Fitness Goal Setting
Use your BMI alongside body fat percentage and BMR to set realistic weight and fitness targets. Knowing your metabolic rate helps you plan calorie intake for muscle gain or fat loss.
Weight Management Programs
Monitor your progress over weeks and months as you follow a diet or exercise plan. Comparing your BMI, ideal weight, and body fat estimates helps you understand whether you are losing fat or muscle.
Medical Screening and Insurance
Many insurance applications and pre-surgical evaluations require a current BMI reading. Use this calculator to check your number before appointments so you know what to expect.
Why Use Our BMI Calculator?
Our comprehensive BMI calculator goes beyond simple body mass index calculations. It provides a complete health assessment including your ideal body weight using multiple formulas (Devine, Robinson, Miller, Hamwi), estimated body fat percentage, and your Basal Metabolic Rate (BMR) with three different calculation methods. Whether you're starting a fitness journey, monitoring your health, or simply curious about your body composition, our calculator provides all the essential metrics in one place with detailed explanations via tooltips.
Body Mass Index (BMI) is calculated by dividing your weight in kilograms by the square of your height in meters: BMI = weight (kg) / height (m)^2. For imperial measurements the formula is BMI = (weight (lbs) x 703) / height (in)^2. The result is a single number that places you into one of several weight categories defined by the World Health Organization.
The WHO classifies BMI into four main brackets: Underweight (below 18.5), Normal weight (18.5 to 24.9), Overweight (25.0 to 29.9), and Obese (30.0 and above). Obesity is further divided into Class I (30-34.9), Class II (35-39.9), and Class III (40+). These thresholds are used worldwide by doctors, nutritionists, and public health agencies to screen for weight-related health risks including heart disease, type 2 diabetes, and hypertension.
While BMI is a useful population-level indicator, it has well-known limitations for individuals. It does not account for muscle mass, bone density, age, or fat distribution. Athletes and bodybuilders often register as overweight or obese despite having low body fat. For a more complete picture of your health, combine BMI with our Body Fat Calculator, TDEE Calculator, and Macro Calculator to understand your body composition, daily energy expenditure, and nutritional needs.
How it compares
Unlike the CDC BMI calculator or NIH BMI tools, the FindUtils BMI Calculator delivers instant results with no data stored on any server. All calculations run entirely in your browser, so your weight, height, and health data remain private. You also get four ideal-weight formulas, three BMR methods, and an estimated body fat percentage in a single page, whereas government calculators typically provide only a basic BMI number. No signup, no email, no personal data collection. Just enter your measurements and get a complete health snapshot in seconds.
BMI Tips & Health Advice
- BMI does not distinguish between muscle and fat. A muscular person can have a high BMI while carrying very little body fat, so always consider body composition alongside your score.
- The standard BMI categories were developed primarily from studies on European populations. Results may be less accurate for people of South Asian, East Asian, or African descent, where different cutoffs are sometimes recommended.
- A normal BMI (18.5 to 24.9) does not guarantee good health. Factors such as blood pressure, cholesterol, blood sugar, and physical activity level matter just as much as your weight-to-height ratio.
- BMI tends to overestimate body fat in tall individuals and underestimate it in shorter people. If you are significantly above or below average height, pair BMI with waist circumference or a body fat measurement for better accuracy.
- For children and teenagers, BMI is interpreted using age- and sex-specific percentile charts rather than the fixed adult categories. This calculator is designed for adults aged 18 and older.
Frequently Asked Questions
What is BMI and how is it calculated?
BMI (Body Mass Index) is a simple calculation using your height and weight. The formula is: BMI = weight (kg) / height (m)squared. For imperial measurements, it's: BMI = (weight (lbs) x 703) / height (inches)squared. BMI provides a numerical value that categorizes you into underweight (<18.5), normal weight (18.5-24.9), overweight (25-29.9), or obese (30+).
What's the difference between the ideal weight formulas?
Each formula was developed at different times with different populations. Devine (1974) is most commonly used in medicine. Robinson (1983) gives more conservative estimates. Miller (1983) tends to give higher ideal weights. Hamwi (1964) is one of the oldest. We recommend comparing results from multiple formulas rather than relying on just one.
Which BMR formula should I use?
Mifflin-St Jeor (1990) is generally considered the most accurate for most people. Harris-Benedict is a classic formula but may overestimate for overweight individuals. Katch-McArdle is best for athletic individuals as it uses lean body mass, but requires knowing your body fat percentage.
How accurate is the body fat percentage estimate?
Our body fat percentage uses a BMI-based formula that provides a reasonable estimate but has limitations. It's most accurate for average adults and may be less reliable for very muscular individuals, the elderly, or those with unusual body compositions. For precise measurements, consider methods like DEXA scans, hydrostatic weighing, or professional body composition analysis.
Why do I need to enter my age and gender?
Age affects body fat percentage calculation and BMR. Gender is crucial because men and women have different base values in ideal weight formulas, different healthy body fat ranges, and different metabolic rates. All three BMR formulas and the body fat estimation require gender for accurate calculations.
What is a healthy BMI range for adults?
The World Health Organization defines a healthy BMI as 18.5 to 24.9 for adults. However, optimal ranges can vary slightly by age, ethnicity, and body composition. People over 65 may benefit from a slightly higher BMI (23-27), and some Asian populations use a lower overweight threshold of 23 instead of 25.
Is BMI accurate for athletes and muscular people?
BMI often overestimates body fat in muscular individuals because it cannot distinguish between muscle mass and fat mass. A bodybuilder with 8% body fat could register as obese by BMI alone. If you exercise regularly and carry significant muscle, use a body fat calculator or waist-to-hip ratio alongside BMI for a more accurate assessment.
How often should I check my BMI?
For general health monitoring, checking your BMI once a month is sufficient. If you are actively trying to lose or gain weight, weekly checks can help track trends, but avoid obsessing over daily fluctuations caused by water retention, meals, and exercise. Focus on the long-term trend over 4 to 8 weeks rather than any single reading.
Can BMI predict health risks?
BMI is a useful screening tool that correlates with increased risk of heart disease, type 2 diabetes, hypertension, sleep apnea, and certain cancers at higher values. However, it is not a diagnostic tool. People with a normal BMI can still have metabolic risk factors, and some people with higher BMIs are metabolically healthy. Blood tests and other clinical assessments provide a more complete risk picture.
What is the difference between BMI and body fat percentage?
BMI is a ratio of weight to height and does not directly measure fat. Body fat percentage tells you exactly how much of your total weight is fat tissue. Two people with the same BMI can have very different body fat levels depending on muscle mass, bone density, and body frame. Body fat percentage is a more accurate indicator of health, but BMI is easier to calculate and widely used for quick screening.