A fluid meter has a housing comprising a flow channel for fluid to be measured and at least one elongate module-receiving opening forming a passage from an outer surface of the housing to the flow channel. At least one fluid-measuring module, prefabricated separately, from the housing with a base section formed as a waveguide for surface acoustic waves, and at least one signal transformer to excite surface acoustic waves in the waveguide and/or receive surface acoustic waves from the waveguide is provided. When inserted into the module-receiving opening, the base section of the fluid-measuring module forms part of the flow channel inner wall and contacts fluid flowing through it. Surface acoustic waves emitted by the signal transformer can be coupled out of the waveguide and can propagate through fluid in the flow channel as bulk acoustic waves and/or bulk acoustic waves can be coupled into the waveguide and received by the signal transformer.