The BMI of adult health is 18.5-23.9, so yours is normal.
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BMI calculation method
The formula is: body mass index (BMI)= weight (kg)/height (m). For example, if a person's height is 1.75m and his weight is 68kg, his BMI=68/( 1.75)? =22.2 (kg/m), which is normal when this index is between18.5 ~ 23.9.
BMI value-Baidu encyclopedia