For mechanical engineering strength design applications it is accepted that shear strength is approximately 60% of tensile strength.
If UTS = 'x' (Ultimate Tensile Strength) - This is the value usually reported in handbooks.
then USS = 60% of 'x'; i.e. 0.6*UTS
If you are looking at YS (Yield Strength)
then SYS = 60% of YS; i.e. 0.6*YS
Each, of course, are entirely different and using them is dependant on what failure criteria you are applying.