Calculating adult BMI from weight and squared height
Body mass index compares weight with squared height. Adult BMI categories are a screening aid that can prompt further discussion, not a measure of health by themselves.
The result highlights the adult category selected using the unrounded BMI. The displayed number is rounded to one decimal place, so a value close to a boundary is classified using its full precision.
The calculator converts centimeters to meters before computing BMI and highlights the adult screening range using the unrounded value. The page explains why a rounded headline can sit close to a category boundary.
How kilograms, centimeters and adult age determine the BMI reading
The arithmetic gives a weight-to-height ratio. Its category is an adult screening label, not an individual diagnosis.
- Weight in kilograms
- Weight is the numerator, so a higher entered weight increases BMI at the same height. It does not tell the calculator how much is muscle or fat.
- Height in centimeters
- Height is converted to meters and squared in the denominator. Check the unit carefully: entering 1.75 as though it were centimeters is not the same as entering 175 cm.
- Age in completed years
- The category display is restricted to people aged 20 or older. Age does not appear in the BMI formula; it selects whether these adult screening ranges apply.
- Screening ranges
- The displayed international adult categories use 18.5, 25 and 30 kg/m² boundaries. Additional 23 and 27.5 discussion points for some Asian populations do not diagnose an individual's risk.
Steps
- Enter body weight in kilograms.
- Enter height in centimeters and age in whole years; this tool supports adults age 20 or older.
- Calculate to see BMI and the adult screening range.
Reading tip: Read the numerical BMI and highlighted adult category together. The 30+ category has no upper limit; larger values remain visible numerically.
Adult screening comparisons this BMI value can support
Adult screening
Calculate the BMI value from height and weight.
Category context
See where the numeric result sits among standard adult ranges.
Measurement checks
Check that centimeters are converted to meters before squaring.
Health conversations
Bring the screening result to a clinician for individual interpretation.
How the calculation works
- BMI
- Body mass index, expressed as kilograms per square meter.
- weight
- Entered body weight in kilograms.
- height
- Entered height in centimeters, converted to meters before squaring.
- ²
- Square the height in meters, then divide weight by that result.
BMI is a screening measure for adults; it does not directly measure body fat or diagnose health.
What every part means
- BMI
- Body mass index, expressed as kilograms per square meter.
- weight
- Entered body weight in kilograms.
- height
- Entered height in centimeters, converted to meters before squaring.
- ²
- Square the height in meters, then divide weight by that result.
Calculate it step by step
The BMI denominator uses meters, not centimeters.
For 1.75 m, the denominator is 3.0625 m².
Adult categories use the unrounded result at cutoffs of 18.5, 25 and 30.
The calculator converts centimeters to meters, squares that number and divides kilograms by the result. It checks that age is at least 20 because child and teen interpretation uses different growth references.
See how Calculation Guide tests examples and handles calculation limits.
See it in practice
- Weight
- 70 kg
- Height
- 175 cm
- Age
- 30 whole years
70 kg and 175 cm: 175 ÷ 100 = 1.75 m; BMI = 70 ÷ 1.75² = 22.857…, displayed as 22.9.
- Adult screening rangeHealthy weight
- Height in meters1.75
Interpretation & limitations
How to read your result
BMI can support a conversation about health, but factors such as muscle mass, medical history and body composition matter. For some Asian populations, a WHO expert consultation proposed additional public-health action points at 23 and 27.5 kg/m² while retaining 25 and 30 as international classifications. No single lower cutoff diagnoses risk for every Asian person.
Where this estimate stops
This adult screening tool is not for children or pregnancy. It does not diagnose a condition or account for individual body composition; a healthcare professional can interpret it in context.
Frequently asked questions
01Can BMI diagnose a health condition?
No. It is a screening measure and should be interpreted with other health information.
02Why must I be at least 20?
Children and teens use age- and sex-specific growth charts instead of these adult screening categories.
03Why can a muscular person have a high BMI?
BMI uses only weight and height, so it cannot distinguish muscle from body fat.
04Why can the rounded number look close to a different range?
The category uses the unrounded BMI; the headline is rounded to one decimal place.
05Is 40 the maximum BMI shown?
No. The 30+ category has no upper limit, and the numeric result can be higher than 40.
06Can this tell me how much body fat I have?
No. BMI is an indirect screening measure and does not calculate body-fat percentage.
07Are BMI cutoffs different for Asian adults?
A WHO expert consultation retained the international 25 and 30 classifications but proposed 23 and 27.5 kg/m² as additional public-health action points because risk can rise at lower BMI in some Asian populations. These are discussion points, not a personal diagnosis or a universal replacement cutoff.