I have -5.5 spherical and -.5 cylindrical power with axis 10, what should be my contact lens power?

Contact lens fitting: You really need to be properly fitted for contacts. For contacts, you not only need the power, but you also need the diameter of the contact lens and a base curve. Both these two numbers describe the shape of the contact lens and you need to be evaluated to see which lens provides the best fit for your eyes. A poorly fitted contact lens may increase the risk for eye infections.