The need to improve miniaturization and device performance in the microchip and microelectronics industry has recently inspired many investigations into supramolecular chemistry. Specifically, the ability to precisely control the inner and outer diameters of self-assembled lipid nanotubes (LNTs) directly determines their suitability for technological applications. Understanding how structural variation affects nanotube dimensions at the molecular level would facilitate a more efficient and systematic approach to generating rationalized tubular libraries. This review summarizes recent advances as well as approaches to controlling the dimensions of lipid and polymer nanotubes, focusing on the outer and inner diameters, lengths, and membrane wall thickness. Some of the methods considered include chiral molecular self-assembly, packing-directed self-assembly, polymer assembly, molecular sculpting, and templated synthesis using a pore.