Method for determining the mass-flow of a fluid comprising the steps: a) recording a series of measurements { Q i, Δ T ' i, Δ T " i} i=1...n where n ≥ 2 measuring points with a first constant mass-flow and constant temperature of the fluid at a first temperature measuring point, wherein a heating effect Q is applied to the fluid at each measuring point by means of a heat transfer element, the heating effect being changed in relation to the preceding measuring points, wherein Δ T ' is the temperature difference between a third temperature measuring point and a first temperature measuring point, and Δ T " is the temperature difference between the third temperature measuring point and a second temperature measuring point, wherein the first temperature measuring point is arranged upstream in relation to the heat transfer element and the second temperature measuring point is arranged downstream in relation to the heat transfer element, and the heat transfer element exhibits a constant surface temperature in the direction of flow, which can be detected by means of the third temperature measuring point; b) extending by the addition of the values Q, Δ T ', and Δ T " of the recorded series of measurements { Q i, Δ T ' i, Δ T " i} i=1...n with in each case systematic errors F Q, F ΔT', and F ΔT" and introduction of the extended series of measurements into both a first function A as well as into a second function B, different from the function A, both of which exclusively link the same values Q, Δ T ', and Δ T " and the specific heat capacity c p of the fluid, wherein, as the first function A for the mass-flow, the function m ̇ A Q ̇, Δ T ′, Δ T ": = Q ̇ c p Δ T ′ − Δ T ". is selected, and as the second function B for the mass-flow the further function m ̇ B Q ̇, Δ T ′, Δ T ": = 1 R Q ̇, Δ T ′, Δ T " c p ln Δ T ′ Δ T " with R = f Q ̇, Δ T ′, Δ T " wherein R is the rise of the function Δ T m = Δ T ′ − Δ T " ln Δ T ′ Δ T " = f Q ̇, which is determined by linear approximation of the series of measurements, and ln Δ T ′ Δ T " designates the natural logarithm of the quotient from Δ T ' and Δ T ", and by combining the results from the first function A and the results of the second function B to a common data quantity; c) varying the systematic errors F Q, F ΔT', and F ΔT" as free fit parameters by the use of a fit function, in which the scatter of the common data quantity is minimised, as a result of which the fit function supplies a value for the constant mass-flow m. a) recording a series of measurements { Q i, Δ T ' i, Δ T " i} i=1...n where n ≥ 2 measuring points with a first constant mass-flow and constant temperature of the fluid at a first temperature measuring point, wherein a heating effect Q is applied to the fluid at each measuring point by means of a heat transfer element, the heating effect being changed in relation to the preceding measuring points, wherein Δ T ' is the temperature difference between a third temperature measuring point and a first temperature measuring point, and Δ T " is the temperature difference between the third temperature measuring point and a second temperature measuring point, wherein the first temperature measuring point is arranged upstream in relation to the heat transfer element and the second temperature measuring point is arranged downstream in relation to the heat transfer element, and the heat transfer element exhibits a constant surface temperature in the direction of flow, which can be detected by means of the third temperature measuring point; b) extending by the addition of the values Q, Δ T ', and Δ T " of the recorded series of measurements { Q i, Δ T ' i, Δ T " i} i=1...n with in each case systematic errors F Q, F ΔT', and F ΔT" and introduction of the extended series of measurements into both a first function A as well as into a second function B, different from the function A, both of which exclusively link the same values Q, Δ T ', and Δ T " and the specific heat capacity c p of the fluid, wherein, as the first function A for the mass-flow, the function m ̇ A Q ̇, Δ T ′, Δ T ": = Q ̇ c p Δ T ′ − Δ T ". is selected, and as the second function B for the mass-flow the further function m ̇ B Q ̇, Δ T ′, Δ T ": = 1 R Q ̇, Δ T ′, Δ T " c p ln Δ T ′ Δ T " with R = f Q ̇, Δ T ′, Δ T " wherein R is the rise of the function Δ T m = Δ T ′ − Δ T " ln Δ T ′ Δ T " = f Q ̇, which is determined by linear approximation of the series of measurements, and ln Δ T ′ Δ T " designates the natural logarithm of the quotient from Δ T ' and Δ T ", and by combining the results from the first function A and the results of the second function B to a common data quantity; c) varying the systematic errors F Q, F ΔT', and F ΔT" as free fit parameters by the use of a fit function, in which the scatter of the common data quantity is minimised, as a result of which the fit function supplies a value for the constant mass-flow m.