Body Mass Index, or BMI, is a quick screening number that relates your weight to your height. It is widely used by clinicians and fitness sites as a first-pass indicator of whether a person's weight falls in a healthy range. It is easy to calculate and easy to compare over time.
How BMI is calculated
BMI divides your weight by the square of your height. In metric units the calculation is direct; in imperial units a conversion factor of 703 keeps the math consistent.
Metric: BMI = weight(kg) / height(m)^2 Imperial: BMI = 703 * weight(lb) / height(in)^2
BMI categories
- Below 18.5: underweight
- 18.5 to 24.9: normal (healthy) weight
- 25 to 29.9: overweight
- 30 and above: obese
Calculating your BMI in a few steps
- Choose metric or imperial units
- Enter your height and weight in the matching fields
- Read your BMI value and the category it falls into
- Recheck periodically to track changes over weeks or months
A worked example
Suppose you weigh 70 kg and stand 1.75 m tall. Squaring the height gives 3.0625, and 70 divided by 3.0625 is about 22.9. That falls in the 18.5 to 24.9 band, so this person is in the normal range.
Used as one signal among many, BMI is a fast and useful checkpoint. The BMI Calculator handles both unit systems and the category lookup so you get a clear, accurate reading in seconds.
Limitations that are worth knowing
BMI is a screening number built from height and weight only, so it says nothing about body composition. A heavily muscled athlete can land in the overweight band while carrying little body fat; the elderly and children sit in ranges where BMI was never calibrated. Treat the category as a conversation starter with a healthcare professional, not a verdict — it is most informative for generally sedentary adults in the 20–65 age range.
- Interpret “obese” and “underweight” bands as prompts for a professional check.
- Waist circumference and activity level belong in the same conversation.
- Trend matters more than a single reading: track it over time.
