BMI for 181 cm and 40 kg
BMI 12.2
Asia-Pacific cut-offs (23 · 25) · underweight
WHO international cut-offs (25 · 30) · underweight
Reference weight and healthy range
At BMI 22 the reference weight is 72.1 kg.
The healthy range (BMI 18.5–22.9) is 60.6–75 kg.
That is 20.6 kg below the bottom of the range.
Other pairs that also give BMI 12.2
Nearby heights and weights
BMI cannot tell muscle from fat, so it reads high for people who train heavily. It is a reference figure, not a diagnosis.