BMI calculator
Calculate body mass index from height and weight.
Fill in the fields and the result will appear here automatically.
The BMI calculator estimates body mass index from height and weight and assigns a general weight category. It is useful for a quick health screening, tracking long-term changes or preparing for a conversation with a doctor or coach. BMI is not a diagnosis, but it gives a simple starting point.
How it works
Formula and logic
BMI is calculated by dividing weight in kilograms by height in meters squared. In US-style inputs, the calculator first converts pounds and inches into metric units before applying the same formula. The result is compared with standard adult ranges: below 18.5 is commonly considered underweight, 18.5 to 24.9 is the healthy range, 25 to 29.9 is overweight and 30 or higher is obesity. The formula is intentionally simple, which makes it useful for population-level screening, but it does not measure body fat directly. It does not know how much of your weight is muscle, bone, water or fat, and it does not account for age, sex, pregnancy, athletic training or fat distribution. Because of that, BMI should be interpreted as a general signal rather than a complete health assessment.
Example
A user enters 82 kilograms and 178 centimeters. The calculator converts height to 1.78 meters, then computes BMI using the standard formula. The result is about 25.9, which falls in the overweight range for adults. This does not automatically mean the person is unhealthy, but it suggests that waist size, activity level, blood pressure, lab results and body composition may be worth checking. If the user lifts weights regularly, the result should be interpreted together with muscle mass and waist measurement.
Fields and units
- Height — unitless
- Weight — unitless
How to use
- — Enter height in centimeters.
- — Enter weight in kilograms.
- — Check BMI and category.
The most common mistake is treating BMI as a final verdict. A muscular athlete can have a high BMI with low body fat, while an older adult can have a normal BMI but low muscle mass. BMI also says nothing about where fat is stored, even though abdominal fat is often more relevant to health risk. Measure height and weight consistently, preferably without shoes and at a similar time of day. Do not overreact to daily weight swings after meals, travel or training. For a fuller picture, combine BMI with waist circumference, waist-to-height ratio, fitness level, medical history and professional advice. If the result is in an extreme range or changes quickly without explanation, it is worth discussing with a healthcare professional.
Sources and review status
- Calculation method
- BMI is weight in kilograms divided by height in meters squared.
- Data or methodology source
- WHO: BMI formula and interpretation limits
- Last reviewed
- Limitation
- Adult cutoffs do not measure body fat directly and may be unsuitable for children, pregnancy, older adults or muscular athletes.
FAQ
What is a healthy BMI range?
For most adults, a BMI between 18.5 and 24.9 is commonly considered the healthy range. Below 18.5 may indicate underweight, while 25 and above falls into overweight or obesity ranges. These categories are general screening ranges and do not replace an individual medical assessment.
Is BMI accurate for athletes?
BMI can be misleading for athletes because it does not distinguish muscle from fat. A strength athlete may have a high BMI because of lean mass, not excess body fat. In that case, body composition, waist circumference and performance context provide better information than BMI alone.
Why can BMI be misleading?
BMI uses only height and weight. It ignores age, sex, muscle mass, bone structure and where fat is stored. Two people with the same BMI may have very different health profiles. That is why BMI is best used as a quick screening tool, not a complete diagnosis.
Can children use the adult BMI ranges?
No. Children and teenagers should be assessed with age- and sex-specific BMI percentiles, not adult cutoffs. Growth patterns change quickly, so adult categories can misclassify children. If you need to evaluate a child’s weight, use pediatric charts or speak with a healthcare professional.
What should I do if my BMI is high?
First, confirm that height and weight were entered correctly. Then consider waist size, activity, nutrition, sleep and medical history. A high BMI is a reason to look deeper, not to panic. If it stays high or comes with health concerns, discuss it with a doctor or qualified dietitian.