Getting an accurate blood pressure reading starts with using the right cuff size and placing it correctly on your arm. A cuff that’s too small can inflate your systolic reading by 5 to 10 points, potentially leading to a misdiagnosis of high blood pressure. Here’s how to measure your arm, pick the right cuff, and position it properly.
How to Measure Your Arm
You need one measurement: the circumference of your upper arm at its midpoint. To find that midpoint, bend your elbow to 90 degrees and feel for the bony tip of your shoulder and the bony point of your elbow. The midpoint is halfway between those two landmarks. Mark that spot with a pen or just hold your finger there.
Straighten your arm and let it hang relaxed at your side. Wrap a flexible tape measure around your bare upper arm at the midpoint. Pull the tape snug against the skin so it contacts the full circumference without pressing into the flesh. Read the number in centimeters. That’s the measurement you’ll use to choose your cuff size.
Choosing the Right Cuff Size
Blood pressure cuffs come in four standard adult sizes based on mid-arm circumference:
- Small adult: 26 cm or less
- Adult (regular): 27 to 34 cm
- Large adult: 35 to 44 cm
- Extra-large adult: greater than 44 cm
Most home monitors ship with a regular adult cuff. If your arm falls outside that 27 to 34 cm range, you’ll need to buy a monitor that includes the appropriate cuff or purchase a compatible one separately. The American Heart Association recommends an automatic, cuff-style, upper-arm monitor and advises against wrist or finger monitors because they produce less reliable readings.
Using the Index Line on the Cuff
Many cuffs have a built-in fit check. When you wrap the cuff around your arm, look for a line labeled “INDEX” along the edge of the cuff. The inside of the cuff will also have two “RANGE” lines. If the index line falls completely within those range lines, the cuff fits. If it barely fits or falls outside the range, move up to the next larger size. This takes about two seconds and is the most reliable way to confirm fit without a tape measure on hand.
Where to Place the Cuff
Wrap the cuff around your bare upper arm, positioning the bottom edge about one inch (roughly 2.5 cm) above the bend of your elbow. Never place it over clothing, as even a thin sleeve can distort the reading.
Most cuffs have an artery marker, usually a small line or arrow printed on the outside. Align that marker with your brachial artery, which runs along the inner side of your upper arm. You can find it by pressing two fingers into the crook of your elbow, slightly toward the inside of your arm, and feeling for a pulse. The center of the cuff’s inflatable bladder should sit directly over that artery. Research on cuff positioning shows that rotating the bladder away from the artery significantly reduces accuracy.
How Tight Should the Cuff Be
Secure the cuff firmly but not tightly. A common check is to slide one or two fingertips between the cuff and your skin. If you can do that with slight resistance, the fit is right. If you can easily slide your whole hand underneath, it’s too loose. If you can’t fit a finger in at all, it’s too tight. Both extremes will skew your reading.
Getting Your Arm in the Right Position
Rest your cuffed arm on a table or solid surface so the middle of the cuff sits at chest height, roughly level with your heart. Letting your arm hang at your side or holding it up unsupported will change the reading. Sit with your back supported, feet flat on the floor, and legs uncrossed. The CDC notes that crossing your legs and letting your arm droop can both raise your blood pressure reading.
What Happens With the Wrong Cuff Size
An undersized cuff is the most common fitting error, and it consistently pushes readings higher than your actual blood pressure. The overestimate runs about 5 to 10 mmHg for systolic pressure and 2 to 6 mmHg for diastolic pressure. If the mismatch is more than one size off, the error grows even larger. That’s enough to push a normal reading into the hypertension range and lead to unnecessary treatment.
An oversized cuff does the opposite, producing readings that are falsely low. This is less common but can mask genuinely high blood pressure.
Cone-Shaped Arms Need Special Cuffs
If you carry significant weight in your upper arms, a standard rectangular cuff may not make even contact with the skin. Larger arms tend to be cone-shaped rather than cylindrical, with the upper part of the arm wider than the lower part. Standard cuffs are designed for cylindrical arms, and when wrapped around a cone-shaped arm, they transmit pressure unevenly. In a study of obese participants, standard cylindrical cuffs overestimated systolic blood pressure by about 5 mmHg on average, and by as much as 9 mmHg in those with the highest blood pressure. Cone-shaped (tronconic) cuffs are designed to solve this problem and are worth seeking out if your arm circumference exceeds 44 cm.
Quick Steps for an Accurate Reading
- Measure your arm at the midpoint between shoulder and elbow, in centimeters.
- Select a cuff that matches your circumference range, and confirm the index line falls within the range markers.
- Place on bare skin one inch above the elbow crease, artery marker aligned with the inside of your arm.
- Check tightness by sliding one to two fingers underneath the cuff.
- Support your arm on a flat surface at heart height, back supported, feet on the floor, legs uncrossed.