What fraction of the arm should the cuff bladder encircle for accurate blood pressure measurement?

• A. 100%
• B. 80% of the arm
• C. 50%
• D. 90%

Answer: (B)

Accurate blood pressure depends on a cuff that wraps around a substantial portion of the upper arm so the artery is compressed evenly. The bladder should encircle about 80% of the arm. This size provides enough coverage to occlude the brachial artery reliably without being so wide that the pressure readings become unreliable or so narrow that they exaggerate the result. If the cuff covers much less than that, the occlusion is uneven and readings tend to be inaccurate; if it covers nearly the whole arm, it can distort the pressure translation to the artery. So 80% is the standard fraction that balances proper occlusion with accurate measurement.