A method for measuring the flow rate in sewer pipes, wherein an image of the sewer pipe cross-section with the flow level of the liquid flow in the sewer pipe visible therein as a horizontal boundary line is generated from a sewer shaft by means of an optical camera, and the actual flow cross-section of the liquid is calculated from the flow cross-sectional area limited in the image by the flow level in relation to the total cross-sectional area of the cross-sectional image of the sewer pipe and the known geometry and dimensions of the sewer pipe, and the flow rate per unit time is calculated therefrom as well as from a determined flow velocity of the liquid flow, characterised in that the flow velocity of the liquid flow is derived from a measurement of the inclination of the sewer pipe by means of a measurement device positioned in the sewer shaft and having an optical camera and a laser that, by means of a diffractive lens, creates a plurality of narrow annular laser beams in the form of thin cone surfaces with different convergence angles, wherein the optical axes of the laser and the camera extend in parallel and the camera/laser combination (1, 2) is placed with the optical axis of the laser centered in relation to the cross-section of the sewer pipe, wherein the measurement is performed according to one the following two methods: a) the camera/laser combination is oriented with their optical axes exactly horizontally, and laterally in a vertical plane containing the axis of the sewer pipe, so that the plurality of laser beams incident on the sewer wall create axially spaced circular incident lines that are inscribed as more or less eccentric in the image viewed by the camera, depending on the inclination of the sewer pipe, wherein, from the quantity of eccentric registration of the incident lines of the laser beams in the image seen by the camera, the inclination of the sewer pipe is calculated, or b) the inclination of the camera/laser combination (1, 2) is adjusted in a way that the optical axis of the laser that is aligned in the vertical plane containing the axis of the sewer pipe extends in parallel to the axis of the sewer pipe, which occurs when the incident lines of the laser beams created by the plurality of laser beams on the sewer wall on the image detected by the camera have an exactly concentric extension, and the adjusted inclination of the camera/laser combination (1, 2) thus corresponds to the inclination of the sewer pipe. a) the camera/laser combination is oriented with their optical axes exactly horizontally, and laterally in a vertical plane containing the axis of the sewer pipe, so that the plurality of laser beams incident on the sewer wall create axially spaced circular incident lines that are inscribed as more or less eccentric in the image viewed by the camera, depending on the inclination of the sewer pipe, wherein, from the quantity of eccentric registration of the incident lines of the laser beams in the image seen by the camera, the inclination of the sewer pipe is calculated, or b) the inclination of the camera/laser combination (1, 2) is adjusted in a way that the optical axis of the laser that is aligned in the vertical plane containing the axis of the sewer pipe extends in parallel to the axis of the sewer pipe, which occurs when the incident lines of the laser beams created by the plurality of laser beams on the sewer wall on the image detected by the camera have an exactly concentric extension, and the adjusted inclination of the camera/laser combination (1, 2) thus corresponds to the inclination of the sewer pipe.