Use this BMI Calculator to quickly calculate BMI from height and weight and understand what the result may mean for your general weight category. BMI (Body Mass Index) is a widely used screening measure that estimates body size and can help indicate whether weight is in a healthy range for a given height.
Note: BMI is a general indicator, not a diagnosis. A clinician may also consider waist size, medical history, activity level, and other measures.
BMI is a numerical value based on height and weight that helps estimate whether a person is underweight, at a healthy weight, overweight, or in an obesity range. It’s commonly used for adults as a quick screening tool and is often used in public health and clinical settings to flag potential weight-related risk.
BMI is useful because it is:
The adult BMI classification commonly used by health organizations groups BMI into ranges like underweight, normal, overweight, and obesity, with obesity often split into classes.
Classification | BMI (kg/m²) |
Severe thinness | < 16.0 |
Moderate thinness | 16.0 – 17.0 |
Mild thinness | 17.0 – 18.5 |
Normal (Healthy) | 18.5 – 25.0 |
Overweight | 25.0 – 30.0 |
Obesity Class I | 30.0 – 35.0 |
Obesity Class II | 35.0 – 40.0 |
Obesity Class III | > 40.0 |
These categories are for adults. For children and teens, BMI is interpreted differently (see below).
For ages 2–20, BMI is usually assessed using BMI-for-age percentiles, because growth and development affect body composition.
Category | Percentile Range |
Underweight | < 5% |
Healthy weight | 5% – 85% |
At risk of overweight | 85% – 95% |
Overweight | > 95% |
If you’re calculating BMI for someone under 20, use a child/teen-specific calculator that references growth charts rather than adult cutoffs.
BMI is best read as a screening signal:
Higher BMI is often associated with increased risk of conditions such as high blood pressure, type 2 diabetes, heart disease, sleep apnea, joint issues, and some cancers. This does not mean a diagnosis—only that further context and health checks may be useful.
Lower BMI may be linked with malnutrition, nutrient deficiencies, lowered immune function, reduced bone density, and other concerns, depending on the cause and overall health. If weight loss is unexplained, professional advice is recommended.
Many BMI calculator pages pair BMI with waist measurement because abdominal fat can add risk even when BMI looks “normal.” Waist size can help estimate risk related to central fat distribution.
Waist measurement is not perfect either and may be less appropriate for some situations (for example pregnancy, children, or certain medical conditions).
BMI is popular because it’s simple, but it cannot measure body fat directly and doesn’t capture body composition. This is why BMI can misclassify some people.
BMI may be less accurate for:
Use BMI as one data point—especially if the result looks surprising compared to how health feels and functions day to day.
BMI = weight (kg) / height² (m²)
BMI = 703 × weight (lb) / height² (in²)
A healthy BMI typically falls between 18.5 and 24.9, though individual factors like age, muscle mass, and overall health should be considered alongside this measurement.
Check your BMI monthly when actively managing weight, or quarterly for general health monitoring to track meaningful changes over time.
Athletes with high muscle mass may show elevated BMI despite low body fat, making additional assessments like body composition analysis more appropriate.
BMI helps identify increased risk for conditions like heart disease, diabetes, and hypertension, though it’s a screening tool, not a diagnostic measure.
While the BMI formula remains constant, interpretation varies slightly for children, teens, and elderly adults, with gender-specific considerations for body composition.
A BMI amputation calculator is a tool that estimates Body Mass Index (BMI) for individuals who have undergone limb amputation by adjusting body weight based on the type and level of amputation. This provides a more accurate BMI compared to standard calculators.
The calculator adds an estimated percentage of body weight corresponding to the missing limb (such as below-knee, above-knee, or arm amputation) before calculating BMI using height and adjusted weight.
BMI amputation calculators use clinically accepted limb weight percentages, but results are estimates. For medical decisions, results should always be reviewed by a qualified healthcare professional.
This calculator is useful for amputees, healthcare professionals, dietitians, fitness trainers, and rehabilitation specialists who need an accurate assessment of body composition and health risk.
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