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Nanoparticles with size in the range from 10 nm to 300 nm and from three different materials (Au 10 nm, Ag 20 nm, and PSL 30 nm, 100 nm and 300 nm) were used in this supplementary comparison. The selected nanoparticles meet the requirements of different measurement methods such as Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS), and Differential Mobility Analyzer (DMA), Small Angle X-Ray Scattering and for forth. All 37 participating laboratories returned results, but not all laboratories were able to perform measurement of all 5 nanoparticles. In order to determine the degree of equivalence (DOE), two reference values were considered in this comparison: the method dependent reference value (MRV) and the global reference value (GRV). The MRVs were determined for different measurement methods according to the corresponding reported uncertainties and measurement values from the participants. Each measurement method owns its own MRV. Since the measurement data from DLS were very different from and inconsistent with the measurement data from the other methods, the MRV for DLS was used in the En number calculation for the measurement data reported from the DLS method. The GRV was determined from the MRVs and their uncertainties of all the measurement methods except DLS, and was applied in the En number calculations for the measurement data reported from AFM, EM, DMA and SAXS methods. The assumption that the particles are spherical was commonly made in the nanoparticle measurements. Non-sphericity of particles, if exists, could have different impacts on different measurement methods. It is also important to note that the methods used are measuring mean diameters of a population of particles, not just a single particle, and that the meaning of the mean diameter could differ for different methods. Probably if participants include a different specific contribution in the uncertainty in a harmonized way, taking the non-cancelled method-dependent "systematic" errors into account, it may be easier to compare the results. KEY WORDS FOR SEARCH Nanoparticles; Atomic Force Microscopy (AFM); Transmission Electron Microscopy (TEM); Scanning Electron Microscopy (SEM); Dynamic Light Scattering (DLS); and Differential Mobility Analyzer (DMA); Small Angle X-Ray Scattering Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

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The question of how to relate particle sizes measured using a fixed-angle dynamic light scattering (DLS) instrument with those measured using a multi-angle DLS instrument is addressed. A series of nearly monodisperse polystyrene latex (PSL) particles with nominal diameters of 100 nm, 70 nm, 50 nm, and 30 nm were measured using two different types of DLS instruments: one owned by the National Metrology Institute of Japan (NMIJ) of the multi-angle type and the other owned by the National Institute of Standards and Technology (NIST) of the fixed-angle type. The mean particle size of the PSL particles was measured using the multi-angle-type instrument at various scattering angles and at various concentrations of particle suspension. These data were used to establish the functional dependence of the measured particle size on the scattering angle and particle concentration through the least-squares fitting method. The established function was then used to predict the mean particle sizes that would have been obtained if the same scattering angle and particle concentrations as those used at NIST had been selected at NMIJ. The mean particle sizes obtained at NIST and at NMIJ agreed quite well for all four PSL particle samples after compensating for the angle and concentration differences. The result of this study clearly demonstrates that consideration for the dependence of measured particle sizes on the scattering angle and particle concentration is crucial in intra-method comparisons of mean particle sizes obtained using DLS.