A flow rate measuring unit (1, 1') for determining the flow rate of a fluid, having 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, wherein - 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 at least one bypass channel branch, - at least one electric sensor arrangement arranged 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, - the insert plates (16, 16') include plate end regions (40, 40') that each have a plate aperture (39, 39'), wherein the plate apertures (39, 39') in the insert plate stack form the branch channel and the mouth channel, and wherein the at least one bypass channel branch and the measuring channel branch branch off the branch channel and open into the mouth channel, - at least some of the insert plates (16, 16') at least 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, and - the channel widening chamber is sealed to the outside by way of a shapeable sealing element that is provided for sealing and disposed on at least one of the housing parts (3, 4), characterized in that - the insert plates (16, 16') of the insert plate stack are pressed against one another in a sealed manner by the at least one other housing part (3, 4), in the case of connected housing parts (3, 4), - a housing gap is formed between the connected housing parts (3, 4) outside the channel widening chamber, wherein the insert plates (16, 16') are situated on top of one another in a defined manner, and the insert plate stack is clamped between the at least two housing parts (3, 4), forming a certain housing gap dimension, and - the insert plate stack protrudes over the channel widening chamber and/or the other housing part (3, 4), which presses the insert plate stack, at least centrally includes an elevation, whereby the housing gap between the at least two housing parts (3, 4) is determined at least in the region of the sealing element provided for sealing. - 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 at least one bypass channel branch, - at least one electric sensor arrangement arranged 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, - the insert plates (16, 16') include plate end regions (40, 40') that each have a plate aperture (39, 39'), wherein the plate apertures (39, 39') in the insert plate stack form the branch channel and the mouth channel, and wherein the at least one bypass channel branch and the measuring channel branch branch off the branch channel and open into the mouth channel, - at least some of the insert plates (16, 16') at least 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, and - the channel widening chamber is sealed to the outside by way of a shapeable sealing element that is provided for sealing and disposed on at least one of the housing parts (3, 4), - the insert plates (16, 16') of the insert plate stack are pressed against one another in a sealed manner by the at least one other housing part (3, 4), in the case of connected housing parts (3, 4), - a housing gap is formed between the connected housing parts (3, 4) outside the channel widening chamber, wherein the insert plates (16, 16') are situated on top of one another in a defined manner, and the insert plate stack is clamped between the at least two housing parts (3, 4), forming a certain housing gap dimension, and - the insert plate stack protrudes over the channel widening chamber and/or the other housing part (3, 4), which presses the insert plate stack, at least centrally includes an elevation, whereby the housing gap between the at least two housing parts (3, 4) is determined at least in the region of the sealing element provided for sealing.