About BMI Calculator
Calculate your Body Mass Index instantly. Enter height and weight to see your BMI score, weight category, healthy range, and health risk level. Free, metric and imperial.
How to use
- Select your preferred unit system: metric (kilograms and centimetres) or imperial (pounds and inches). The calculator converts between systems automatically, so use whichever you are most comfortable with.
- Enter your current weight accurately. For the most consistent measurements, weigh yourself in the morning before eating, wearing light clothing. Weekly averages are more reliable than single readings since body weight fluctuates 1-3 lbs daily due to hydration and food timing.
- Enter your height. If you are unsure of your exact height, stand against a wall and mark the top of your head, then measure from the floor to the mark. Height in centimetres provides more precision than feet and inches.
- View your BMI score, weight category (underweight, normal, overweight, or obese), and the healthy weight range for your height. The healthy BMI range is 18.5-24.9, which translates to a weight range that varies by height — for someone 5'10", healthy weight is roughly 129-174 lbs.
- Check the colour-coded BMI chart to see where you fall on the scale and how far you are from category boundaries. If your BMI is 26, you can see exactly how many pounds you need to lose to reach the normal range.
- Use your BMI as a starting point, not a final verdict. BMI does not distinguish between muscle and fat, so pair it with waist circumference measurements (below 40 inches for men, 35 inches for women) for a more complete health picture.
Frequently asked questions
What is a healthy BMI range?
The World Health Organization defines BMI categories as: underweight (below 18.5), normal weight (18.5-24.9), overweight (25.0-29.9), 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+). The lowest risk of chronic disease is associated with BMI values between 20 and 25. However, BMI is a population-level screening tool, not a diagnostic measure. Individual factors like muscle mass, bone density, age, gender, and ethnicity all affect what constitutes a healthy weight for a specific person.
How is BMI calculated?
BMI = weight in kilograms divided by height in metres squared. In imperial units: BMI = (weight in pounds x 703) / (height in inches squared). For example, a person weighing 170 lbs and standing 5'10" (70 inches): BMI = (170 x 703) / (70 x 70) = 119,510 / 4,900 = 24.4. This formula was developed by Belgian mathematician Adolphe Quetelet in the 1830s and adopted by the WHO as a quick population screening tool. It does not directly measure body fat, which is both its main advantage (simplicity) and its main limitation.
Is BMI accurate for athletes and muscular people?
No, BMI frequently misclassifies muscular individuals as overweight or obese because it cannot distinguish between muscle mass and fat mass. A 6-foot, 220-pound athlete with 12% body fat has a BMI of 29.8 (overweight) despite being in excellent shape. Similarly, BMI may underestimate health risk in people with low muscle mass (sometimes called 'skinny fat') who carry excess visceral fat. For athletes and regular exercisers, body fat percentage (measured via skinfold calipers, DEXA scan, or the Navy method) is a far more accurate indicator of body composition and health risk.
Does BMI apply to children and teenagers?
BMI is calculated the same way for children, but interpretation differs because body composition changes significantly during growth. For children aged 2-20, BMI is plotted on age-and-sex-specific growth charts and expressed as a percentile: underweight (below 5th percentile), healthy weight (5th to 85th), overweight (85th to 95th), and obese (95th percentile and above). A BMI of 22 might be normal for a 16-year-old but overweight for an 8-year-old. Pediatric BMI should always be interpreted by a healthcare provider in the context of growth patterns.
What should I do if my BMI is too high or too low?
If your BMI is above 25, a safe and sustainable approach is to reduce calorie intake by 500 calories per day (creating a 1 lb/week deficit) and increase physical activity to 150+ minutes of moderate exercise per week. Losing even 5-10% of body weight significantly reduces risk of diabetes, heart disease, and joint problems. If your BMI is below 18.5, consult a healthcare provider to rule out underlying conditions and work with a dietitian to increase calorie intake with nutrient-dense foods. Rapid weight changes in either direction should always be discussed with a medical professional. Use the
Calorie Calculator to determine your daily calorie target for a safe, sustainable deficit.
What are the limitations of BMI?
BMI has several well-documented limitations: it does not account for muscle mass (athletes often score as overweight), does not differentiate between visceral and subcutaneous fat (visceral fat around organs is far more dangerous), does not consider fat distribution (waist-to-hip ratio is a better predictor of cardiovascular risk), varies by ethnicity (Asian populations face higher disease risk at lower BMI values, with many health organizations using 23 as the overweight threshold), and does not account for age-related changes in body composition. Despite these limitations, BMI remains a useful first-pass screening tool for the general population.
What is a more accurate alternative to BMI?
Several measurements provide more insight than BMI alone. Waist circumference directly indicates visceral fat: above 40 inches (102 cm) for men or 35 inches (88 cm) for women signals elevated health risk regardless of BMI. Waist-to-hip ratio (WHR) assesses fat distribution: above 0.90 for men or 0.85 for women indicates higher cardiovascular risk. Body fat percentage (measured via DEXA, hydrostatic weighing, or skinfold calipers) directly quantifies fat versus lean mass. For the most practical approach, combine BMI with waist circumference — both are free, require no special equipment, and together provide a reasonably complete picture. For a more precise body composition assessment, use the
Body Fat Calculator which applies the Navy circumference method to estimate your actual fat percentage.
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