Despite the importance of single-wall carbon nanotubes (SWCNTs) coated with short oligos of single-stranded DNA (ssDNA), the structure-specific interactions in these hybrids remain poorly understood. It is known that the interactions can depend on the DNA base sequence and length, and on the nanotube diameter and roll-up angle. To study these phenomena, we are applying a combination of computational and experimental methods. A major goal for guiding and validating molecular dynamics simulations of the hybrid structures is finding the average length of nanotube covered by each ssDNA oligo. We have quantified this by carefully preparing dialyzed aqueous dispersions of SWCNTs in specific oligos and then measuring the absolute mass concentrations of both components using total organic carbon analysis. Corresponding absorption spectra were also measured to deduce ultraviolet SWCNT molar absorptivities (structurally averaged), which in combination with known ssDNA nucleobase absorptivities allow quicker determinations of mass ratios in the hybrids. Our results for a library of hybrids indicate that purine nucleobases on average cover a larger region on the nanotube surface than do pyrimidine nucleobases, as is consistent with the sizes of those aromatic structures. This average coverage is key to developing realistic atomistic molecular dynamics models for the conformations of ssDNA adsorbed on SWCNT sidewalls. Examples of such computed hybrid structures and their significance will be presented.