Flow measuring device for ascertaining flow of a measured medium flowing through a measuring tube, which flow measuring device has a first housing for protruding into the measured medium, wherein the first housing has a first surface intended to face the measured medium, wherein the flow measuring device includes a second surface for bounding the measured medium, and wherein each separation between the first surface for bounding the first housing from measured medium, the second surface for bounding the measured medium and the first surface of the first housing amounts to at least 1 mm.