As a matter of fact, you can measure contact lenses with something called a PD stick, which is the most common thing used in measuring optical device. They are widely used in measuring prescription eyeglasses, too, since the nature of prescription eyeglasses and that of contact lenses are exact the same. Their differences only in one having frames and other not. To measure the curvature of a contact lens, a lens clock is needed. Hope you find this helpful.
Contact lenses are the same as prescription eyeglasses that come in different sizes and curvatures. You can measure the diameter of the lens with a PD stick (optical ruler). Usually, most of contact lenses ranges from from 8 to 14 mm across. Then, you can use a lens clock to measure the curve of a lens. Based on the sizes of the lenses and curvatures, you can easy to get suitable contact lenses.