In 1798, the National Institute and the French minister of foreign relations invited European countries to send delegations of science practitioners to Paris to finalise the values of the metre and the kilogram. This article reads the event as part of a wider attempt to establish the political relevance of international scientific consensus and include scientific exchanges in the diplomatic culture of post-revolutionary Europe. At the end of the 18th century, the scope and methods of both the sciences and diplomacy (...) were being renegotiated. French academicians hoped that the new system of weights and measures would at once facilitate international scientific exchanges and advertise that new authority should be politically invested in savants. During the Directory, part of the political elite hoped to stabilise the Revolution and forge an international order where the Republic could coexist with old regime monarchies. This entailed focusing diplomatic negotiations on commercial development, something a shared metrological system could foster. The conference was the product of the alliance between the two groups. Foreign responses to the project reveal the novelty of the association between scientific discussions and diplomatic negotiations. Furthermore, European savants and governments did not agree that metrological reforms fell primarily under the expertise of science practitioners, rather than under that of trading actors or administrators. The conference did not produce consensus on the suitability of the metric system or on the feasibility of programmes for the unification of weights and measures. It was more successful at promoting precision and rationality as key parameters to assess metrological systems and science practitioners as main experts in the matter. (shrink)