Blood Pressure Measurement Sites: Arm, Wrist, and Leg

Blood pressure can be measured at the upper arm, wrist, forearm, ankle, and thigh, but these sites do not give identical readings. The upper arm remains the clinical standard because it sits close to the heart and produces the most reliable cuff-based readings. Wrist and leg measurements serve real purposes, from home convenience to screening for vascular disease, yet each site introduces its own sources of error that can shift your numbers by ten or more points if you are not careful.

Why Blood Pressure Changes Depending on Where You Measure It

Your blood pressure is not one fixed number throughout your body. As blood travels away from the heart into smaller, stiffer arteries, the systolic (top) number tends to climb while the diastolic (bottom) number and the mean arterial pressure stay roughly the same. In healthy people, systolic pressure in a peripheral artery like the one at the wrist or ankle runs higher than the pressure measured centrally, near the heart.¹ This gradient exists because pressure waves bounce back from branch points in the arterial tree and pile on top of one another, amplifying the peak pressure the further out you go.²

Gravity adds another layer. When you stand up, blood in your legs is subject to a column of hydrostatic pressure that pushes readings higher, while raising a limb above heart level lowers the reading.³ The practical takeaway is simple: the measurement site has to be at heart level, or you need to account for the difference. For every centimeter of height difference between the cuff and the heart, you can expect roughly 0.7 to 0.8 mmHg of error, which adds up fast at the wrist or ankle.

The Upper Arm, Still the Gold Standard

Clinicians default to the brachial artery in the upper arm for a reason. The artery is large enough for a cuff to compress reliably, and when the arm rests on a desk at heart level, the hydrostatic error is essentially zero. But two easily overlooked details can throw off the reading by a clinically meaningful amount: cuff size and arm position.

Cuff Size Errors

Using a cuff that is too small for the arm inflates the reading because the bladder cannot fully compress the artery, so the monitor registers higher pressure than what is actually there. A 2023 randomized crossover trial quantified this precisely. When a regular cuff was one size too small, systolic pressure read about 5 mmHg too high. When it was two sizes too small, the overestimate jumped to roughly 20 mmHg, enough to diagnose hypertension in someone whose pressure is perfectly normal.⁴ Going the other direction, an oversized cuff pushed systolic readings down by about 4 mmHg in the same trial, and a separate study confirmed the same pattern with oscillometric (automated) devices, finding an average drop of about 5.5 mmHg for the oversized cuff.⁵

Most home monitors come with a single “standard” cuff that fits a mid-range arm circumference, typically around 22 to 32 cm. If your arm is larger or smaller than that, the numbers you are getting at home could be consistently wrong. Checking the cuff’s marked range against your actual arm circumference is one of the cheapest improvements you can make for accuracy.

Arm Position Errors

Where your arm rests during the reading matters more than most people realize. A randomized crossover trial of 133 adults tested three common positions: arm supported on a desk at heart level, arm resting on the lap, and arm hanging unsupported at the side. Compared to the desk position, resting the arm on the lap overestimated systolic pressure by about 4 mmHg. Letting the arm hang at the side overestimated systolic pressure by about 6.5 mmHg.⁶ These effects held across subgroups regardless of age, sex, or baseline blood pressure. A reading taken with the arm dangling beside the exam table, which is how it goes in many hurried clinic visits, can push someone from the “elevated” category into the “Stage 1 hypertension” zone on paper alone.

Wrist Monitors Are Convenient but Easy to Get Wrong

Wrist blood pressure monitors are popular for home use because they are compact, easy to put on, and avoid the discomfort of an inflating arm cuff. They work by compressing the radial artery at the wrist, which is shallower and thinner than the brachial artery. Validated wrist devices can meet the accuracy standards set by international protocols when measurements are taken at heart level and within the manufacturer’s specified wrist circumference range.⁷ The problem is that real-world use rarely matches validation conditions.

In a population-based study of people using wrist devices at home, researchers found that most people did not keep the wrist at heart level consistently, leading to frequent detection of falsely elevated readings.⁸ The issue is partly one of memory and habit: the instructions say to hold the wrist at heart level, but people forget or approximate poorly. One engineering analysis calculated that the hydrostatic effect alone accounts for roughly 5 mmHg of error for each shift in wrist height relative to the heart.⁹ If your wrist is resting on a table well below your heart while you sit upright, the added hydrostatic pressure inflates the reading.

A study comparing different arm positions for wrist monitors found that resting the elbow on a desk so the wrist sits naturally at heart height (the “desk” position) produced readings closest to a mercury sphygmomanometer, with a mean systolic difference of about 4 mmHg. Holding the wrist across the chest against the opposite shoulder, a position some manufacturers illustrate, yielded a larger gap of over 13 mmHg.¹⁰ The same study noted that in people with a wide pulse pressure, typically older adults with stiffer arteries, the disagreement between wrist and standard readings tended to be larger. For people in that category, an arm cuff is the safer bet.

Leg Measurements and the Ankle-Brachial Index

Blood pressure at the ankle is not usually taken to manage hypertension. Its main clinical purpose is to calculate the ankle-brachial index (ABI), which compares the systolic pressure at the ankle to the systolic pressure in the arm. In a healthy person, ankle systolic pressure is the same as or slightly higher than arm pressure, producing an ABI between roughly 0.91 and 1.3. The gold standard technique involves using a continuous-wave Doppler ultrasound probe over the ankle arteries while inflating and deflating a cuff on the lower leg.¹¹

An ABI below 0.9 suggests that blood flow to the legs is restricted, typically by atherosclerosis narrowing the arteries. This is the hallmark of peripheral artery disease (PAD), a condition that is often silent in its early stages. A large cohort study of older adults found that about 13% had a low ABI, a group subsequently shown to face elevated cardiovascular risk.¹²

On the opposite end, an unusually high ABI, above roughly 1.3 to 1.4, is not a good sign either. It usually means the arteries in the legs have become calcified and stiff, making them hard to compress with a cuff. The monitor reads an artificially high pressure because the vessel wall resists collapse. This pattern is especially common in people with diabetes or end-stage kidney disease, conditions that promote a specific type of arterial calcification.¹³ A systematic review confirmed that the sensitivity of ABI as a screening tool drops substantially in people with diabetes-related vascular disease because the calcified arteries produce misleadingly high readings.¹⁴ In those cases, clinicians may turn to toe pressures or other imaging to get an accurate picture of blood flow.

When the Standard Upper Arm Will Not Work

Some patients cannot have a standard upper-arm cuff used on one or both arms. The most common scenario is severe obesity, where the upper arm circumference exceeds the range of even the largest available cuffs. For these individuals, placing a properly sized cuff on the forearm and measuring at the radial artery is an alternative that has been validated against intra-arterial (direct) pressure monitoring. In a study of severely obese patients, forearm blood pressure measurement showed high sensitivity and high positive predictive value for detecting hypertension.¹⁵ A follow-up study confirmed that forearm systolic pressure agreed well with the gold standard, particularly when the patient was lying down.¹⁶ Sitting upright introduced more variability, so if you are being measured on the forearm in a clinic, lying back may give a better result.

Another situation that comes up frequently is breast cancer surgery. For decades, healthcare providers have been told to avoid using the arm on the side where lymph nodes were removed, out of concern that cuff compression could worsen or trigger lymphedema. A clinical inquiry into this practice found that the precaution is not well supported by evidence and appears to be based more on tradition than on demonstrated harm.¹⁷ Still, many medical societies continue to recommend the precaution, so in practice you will often see clinicians default to the opposite arm or use the leg instead. It is one of those areas where clinical culture has outrun the evidence, and the policy persists partly because the cost of switching arms is low even if the risk is probably overstated.

What a Difference Between Arms Can Mean

Measuring blood pressure in both arms is a simple screening step that can reveal vascular problems. A systematic review in The Lancet found that a difference of 10 mmHg or more in systolic pressure between the two arms was strongly associated with subclavian stenosis, a narrowing of the artery supplying blood to the arm. In patients confirmed to have significant stenosis by angiography, the mean inter-arm difference was about 37 mmHg. The review concluded that a 15 mmHg or greater difference between arms could serve as a useful marker for vascular disease and an indicator of increased mortality risk.¹⁸

This is why many guidelines suggest checking both arms at least once, particularly at a patient’s first visit. If a consistent difference shows up, the arm with the higher reading becomes the one used for future monitoring, because that arm more accurately reflects the pressure reaching vital organs. A small difference of a few mmHg between arms is normal and nothing to worry about. It is the persistent gaps above 10 or 15 mmHg that warrant a closer look at vascular health.

Invasive Monitoring in Critical Care

Outside the world of cuffs and home monitors, critically ill patients in intensive care units often have blood pressure measured directly through an arterial catheter, a thin line threaded into an artery. The two most common sites for these catheters are the radial artery at the wrist and the femoral artery in the groin. Under normal conditions the readings from these two sites are close, but in certain clinical situations they can diverge significantly.

In septic shock patients receiving high doses of vasopressor drugs, the radial artery consistently underestimates blood pressure compared to the femoral artery. One study found the average gap in mean arterial pressure was about 5 mmHg overall, rising to about 6 mmHg during high-dose vasopressor therapy, with clinically significant differences occurring in up to 62% of those high-dose patients.¹⁹ A similar pattern has been documented during liver transplant surgery, where femoral systolic pressures ran about 16 mmHg higher than radial pressures during the critical reperfusion phase, particularly when vasoconstrictors were in use.²⁰ The practical lesson for intensivists is that when the radial reading looks suspiciously low in a patient on heavy vasopressor support, it probably is, and switching to a femoral line or relying on mean rather than systolic pressure gives a more accurate picture.

Smartwatches and Cuffless Blood Pressure Devices

A growing number of consumer wearables claim to measure blood pressure without a cuff, typically using optical sensors on the wrist that detect changes in blood flow through the skin. The idea is appealing: continuous, effortless monitoring throughout the day, no arm cuff, no fuss. But the technology has real limitations that are still being worked out.

Most cuffless devices require initial calibration with a traditional cuff-based monitor, and their accuracy can drift over time if not recalibrated regularly.²¹ A real-world study of smartwatch-based monitoring involving over 35,000 readings found that the devices were feasible for out-of-office blood pressure tracking, but raised concerns about stability: the seven-day average blood pressure before and after calibration differed by roughly 7 mmHg on average, and the gap was larger in people with higher blood pressure. A separate study using a different smartwatch showed a systematic bias where the device overestimated low pressures and underestimated high ones, essentially pulling readings toward the calibration point.²² That tendency to compress the range is the opposite of what you want in a clinical tool, where catching the highs and lows is the whole point.

For now, cuffless devices are best thought of as trend-tracking tools rather than replacements for validated cuff monitors. They can flag that your pressure seems to be climbing over weeks or months, prompting you to verify with a proper cuff. Treating a single smartwatch reading as a reliable blood pressure value, though, invites the same kind of false confidence that unpositioned wrist cuffs do, but wrapped in sleeker hardware.