Using a blood pressure cuff that's too large or too small can give you inaccurate blood pressure readings. Your doctor's office should have several sizes of cuffs to ensure an accurate blood pressure reading.
Also, when you measure your blood pressure at home, it's important to use the proper size cuff. The inflatable part of the blood pressure cuff should cover about 80 percent of the circumference of your upper arm. The cuff should cover two-thirds of the distance from your elbow to your shoulder.
If you're concerned about the size of your cuff or your blood pressure readings, talk to your doctor. He or she may check your blood pressure several times with the same, appropriately sized, cuff in the same arm. Averaging multiple readings taken during the same visit should give your "true" blood pressure at that point in time.