A new mathematical formula for calculating the symmetry, asymmetry and hypoplasia of blood vessel segments is presented for discussion. The study was conducted using the computed tomography (CT) files from 80 patients (34 men and 46 women) from the Silesian University Hospital, Silesia, Poland, who were between the ages of 12 to 76 and had undergone CT angiography of the circle of Willis. With the use of Gradual Angiographic Image Data Analyser software and double shuttled glasses, CT files were reconstructed. In addition, 80 renal arteries (RAs) from spontaneously aborted foetuses ranging in age from 14 to 30 weeks (24 male and 16 female) were injected with latex and also included in the study. Digital images of the RAs were taken using a Camedia 4040 camera and analysed using original analysis software. A novel formula entitled the Vascular Asymmetry Coefficient (VAC) was derived for this purpose and displays the differences between the mean diameters of blood vessel segments expressed as a percentage of the wider vessel with respect to the major diameter. The asymmetrical classification for a vascular segment of a vessel is given when the difference between the mean diameters of the vascular segment, as represented by the wider vessel, is greater than VAC > 10%. The hypoplastic classification is reserved for blood vessels where the difference between the diameter of the two segments is expressed as a percentage of the wider vessels and is greater than VAC > 40%. While there have been inconsistent and arbitrary classifications for the qualitative criteria of blood vessels, this newly presented algorithm can be used as a standardised tool and has a considerable range of uses, particularly when comparing blood vessel symmetry, asymmetry and hypoplasia prior to bifurcation, and unification.