A metrological calibration facility for particle number counters (PNCs) has been developed at the Physikalisch-Technische Bundesanstalt (PTB) as a primary reference standard for this metric required in the quantification of solid soot emission as described in national and European regulatory frameworks. This study describes the calibration of a Condensation Particle Counter (CPC) using PTB’s primary aerosol number standard, a Faraday Cup Aerosol Electrometer (FCAE). The calibration facility enables high accuracy determination of CPC counting efficiency for particles with mobility diameters between 17 and 200 nm, as well as linearity measurements of particle number concentrations ranging from 1 cm⁻³ to 20 000 cm⁻³. Soot aerosol particles were generated using a miniCAST 5303 and subsequently treating them in a Catalytic Stripper to remove volatile components before homogenisation in an integrated mixing unit. The aerosol flow was distributed via a ten-port manifold, allowing simultaneous evaluation of up to eight CPCs and a FCAE connected to two different ports simultaneously. The results demonstrate that the facility provides state-of-the-art metrological capabilities for CPC calibration, supporting improved reliability and comparability of particle number measurements in emission control applications.