The present disclosure describes a viscometer for measurements of both Newtonian and non-Newtonian fluids. In one embodiment, the viscometer comprises (i) a storage reservoir to store a test fluid, (ii) at least one drain tube assembly comprising a capillary drain tube, (iii) a collector for collecting said test fluid, and (iv) a detector. In addition, its novel viscosity equations suitable for the described viscometers are provided and illustrated for the application to Newtonian fluids and non-Newtonian fluids.