BMI Calculator – Free Body Mass Index Calculator Online
Use our free BMI calculator to instantly find your Body Mass Index. Enter your height and weight to check if you're in a healthy weight range. Supports both metric and imperial units.
BMI (Body Mass Index) is a simple screening tool that relates your weight to your height. It's calculated by dividing weight in kilograms by height in meters squared. The result places you in a category: underweight, normal, overweight, or obese.
BMI was developed in the 1830s by Belgian mathematician Adolphe Quetelet. It's not a diagnostic tool – it doesn't measure body fat directly or account for muscle mass, bone density, or fat distribution. A muscular athlete might have a "high" BMI but low body fat.
Despite its limitations, BMI correlates reasonably well with body fat for most people and predicts health risks at the population level. It's most useful as a starting point, not a final verdict on your health.
| Category | BMI Range | Health Risk | Recommendation |
|---|---|---|---|
| Underweight | < 18.5 | Malnutrition, osteoporosis, weakened immunity | Consult doctor, focus on nutrient-dense foods |
| Normal weight | 18.5 – 24.9 | Lowest risk for weight-related diseases | Maintain current habits, regular exercise |
| Overweight | 25 – 29.9 | Increased risk of heart disease, diabetes | Moderate calorie reduction, increase activity |
| Obese (Class I) | 30 – 34.9 | High risk of cardiovascular disease, type 2 diabetes | Structured weight loss program recommended |
| Obese (Class II) | 35 – 39.9 | Very high risk of serious health conditions | Medical supervision for weight loss advised |
| Obese (Class III) | ≥ 40 | Extremely high risk, life-threatening | Immediate medical intervention may be needed |
Source: World Health Organization (WHO) BMI classification for adults.
Doesn't distinguish muscle from fat
Muscle weighs more than fat per unit volume. A bodybuilder with 10% body fat might have a BMI of 28 (overweight range) while a sedentary person with 25% body fat could have a BMI of 23 (normal). BMI alone can't tell you if you're fit or fat.
Ignores fat distribution
Where you carry fat matters. Belly fat (visceral fat) is more dangerous than fat stored in hips and thighs. Two people with identical BMIs can have very different health risks based on waist circumference and waist-to-hip ratio.
Varies by age, sex, and ethnicity
Older adults naturally lose muscle and gain fat at the same BMI. Women typically have more body fat than men at the same BMI. Asian populations face health risks at lower BMIs – some countries use cutoffs of 23 for overweight, 27.5 for obese.
| Height | Healthy Weight Range (kg) | Healthy Weight Range (lbs) |
|---|---|---|
| 5'0" (152 cm) | 43 – 58 kg | 95 – 128 lbs |
| 5'2" (157 cm) | 46 – 62 kg | 102 – 136 lbs |
| 5'4" (163 cm) | 49 – 66 kg | 108 – 145 lbs |
| 5'6" (168 cm) | 53 – 70 kg | 115 – 154 lbs |
| 5'8" (173 cm) | 56 – 75 kg | 122 – 164 lbs |
| 5'10" (178 cm) | 59 – 79 kg | 129 – 174 lbs |
| 6'0" (183 cm) | 63 – 84 kg | 137 – 184 lbs |
| 6'2" (188 cm) | 66 – 89 kg | 145 – 195 lbs |
These ranges assume adult height. Growing children and teens should use age-specific BMI percentiles, not adult cutoffs.
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. However, "healthy" depends on individual factors. Some research suggests the lowest mortality risk is actually in the 22-27 range, especially for older adults.
Is BMI accurate for athletes?
No. Athletes with high muscle mass often have BMIs in the overweight or obese range despite having low body fat. NFL linemen average BMI of 30+ but many are under 15% body fat. Athletes should use body fat percentage, not BMI.
What BMI is considered obese?
BMI of 30 or higher is classified as obese. This is further divided into Class I (30-34.9), Class II (35-39.9), and Class III (40+), sometimes called "morbid obesity." Each class carries progressively higher health risks.
Does BMI apply to children?
Children use BMI-for-age percentiles, not adult cutoffs. A child's BMI is compared to others of the same age and sex. Underweight is <5th percentile, healthy is 5th-85th, overweight is 85th-95th, obese is ≥95th percentile.
Should I lose weight if my BMI is high?
Not necessarily. If you're muscular, your high BMI isn't a concern. If you have excess body fat, weight loss may improve health. But focus on behaviors (diet quality, activity, sleep) rather than the number. Small, sustainable changes beat crash diets.
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