What unit is used for velocity in arterial Doppler?

• A. mm/s
• B. m/s
• C. km/h
• D. cm/s

Answer: (D)

Velocity in arterial Doppler is expressed in centimeters per second. Arterial blood flow speeds typically fall in the tens to a few hundreds of centimeters per second, so using cm/s keeps the numbers within a convenient and familiar range and aligns with common reference values used in vascular studies. While the same speed can be written as meters per second (for example, 100 cm/s equals 1 m/s), the standard practice in Doppler reporting is cm/s because it makes typical arterial velocities—like a peak systolic velocity around 100 cm/s—easy to read at a glance. Other units, such as millimeters per second, would yield larger numbers for the same speeds and are less common in practice, and kilometers per hour is not suited to the scale of blood flow in vessels.