Umm... like.. all and every practice approved by human rights I guess, your question has zero context.
Answer: Cover 45% to 50% of the arm circumference
Explanation: Using of a blood pressure cuff can sometimes be an herculean tasks. It is required to use the right size not too large and not too small so as to get the most precise blood pressure readings.
It is required when measuring your blood pressure, that a proper size cuff is used. It is also very important that the bladder (inflatable part) of the blood pressure cuff should cover atleast 45% to 50% of the arm circumference.
