A flow rate measuring unit (1, 1') for establishing the flow rate of a fluid, with a housing, which includes at least two housing parts (3, 4) that can be connected to one another and in which a flow passage extends at least in one of the housing parts (3, 4) from a housing inlet to a housing outlet of the housing, the flow passage in an intermediate region comprising a measuring channel branch and at least one bypass channel branch, whereby - the flow passage, in the intermediate region, comprises a channel widening chamber, in which an insert plate stack composed of at least two insert plates (16, 16') is disposed, which form the at least one bypass channel branch, - at least one electric sensor system disposed on a substrate is arranged on a wall of the measuring channel branch, - in the channel widening chamber, the flow passage comprises a branch channel from which the at least one bypass channel branch branches off orthogonally, and a mouth channel, into which the at least one bypass channel branch opens orthogonally, and - at least some of the insert plates (16, 16') in a center region have at least one plate-longitudinal recess (17, 17') extending in the longitudinal direction of the insert plates (16, 16') serving as the bypass channel branch, characterized in that - the measuring channel branch is formed by at least one insert plate (16, 16') of the insert plate stack including at least one plate-longitudinal recess (17, 17') extending in the longitudinal direction of the insert plate (16, 16'), - the measuring channel branch extends parallel to the at least one bypass channel branch, in which, in the channel widening chamber, the measuring channel branch branches orthogonally off the branch channel and subsequently opens orthogonally into the mouth channel, and - the measuring channel branch and the at least one bypass channel branch extend next to or on top of one another. - the flow passage, in the intermediate region, comprises a channel widening chamber, in which an insert plate stack composed of at least two insert plates (16, 16') is disposed, which form the at least one bypass channel branch, - at least one electric sensor system disposed on a substrate is arranged on a wall of the measuring channel branch, - in the channel widening chamber, the flow passage comprises a branch channel from which the at least one bypass channel branch branches off orthogonally, and a mouth channel, into which the at least one bypass channel branch opens orthogonally, and - at least some of the insert plates (16, 16') in a center region have at least one plate-longitudinal recess (17, 17') extending in the longitudinal direction of the insert plates (16, 16') serving as the bypass channel branch, - the measuring channel branch is formed by at least one insert plate (16, 16') of the insert plate stack including at least one plate-longitudinal recess (17, 17') extending in the longitudinal direction of the insert plate (16, 16'), - the measuring channel branch extends parallel to the at least one bypass channel branch, in which, in the channel widening chamber, the measuring channel branch branches orthogonally off the branch channel and subsequently opens orthogonally into the mouth channel, and - the measuring channel branch and the at least one bypass channel branch extend next to or on top of one another.