Medical devices and methods for determining the size of blood vessels are disclosed. In one implementation, a blood vessel sizing device is configured for placement on an area of skin of a patient. The device includes a plurality of radiopaque concentric-circle elements. In one implementation, a blood vessel sizing method includes placing a marker having a plurality of concentric-circle elements on the skin of a patient, imaging a blood vessel of the patient and the device, and comparing the imaged blood vessel to the imaged circles to determine the blood vessel size, the concentric-circle elements allowing a determination of size without errors of parallax.
