Dynamic light scattering (DLS) is a powerful technique for the sizing of nanoparticles and characterization of their properties in the liquid phase. However, the precision of this technique remains unclear and therefore, in the current work, the precision of the DLS technique for sizing polystyrene latex suspensions and the uncertainty of the DLS data are estimated. Precise measurements of the short time correlation function at seven scattering angles and five different concentrations are performed for four kinds of polystyrene latex suspensions with diameters of 30-100 nm. The extrapolations of apparent diffusion coefficients to infinite dilution and to lower angles yield more precise values than those obtained at one angle and one concentration. The extrapolated particle size measured by DLS is compared to the size determined by a differential mobility analyzer (DMA) in air. Before the comparison, the intensity-averaged size measured by DLS is recalculated to the number-averaged size in the case of DMA from the particle size distribution. After the recalculation, consistent values of mean particle diameter are found to be between those obtained by DLS and DMA within the estimated uncertainties.