The assessment of ultrafine particles (UFP) in the Netherlands is becoming increasingly important, but few long-term measurements are available. To address this, a new indicative UFP map has been created based on nearly 100 short-term measurements collected through the CLAIRE project. These short-term measurements were converted into long-term averages using continuous reference measurements. The resulting averages were then linked to various NOx concentrations, allowing the establishment of sector-specific conversion factors. Finally, an overall calibration was applied, as not all measurement devices had the same lower detection limit. The new map provides a more realistic representation of UFP levels and the contributions of different sources in the Netherlands compared to previous versions.