Thermal flow sensor designed to determine the flow of a medium, wherein said sensor comprises: - a substrate; - a first and a second temperature sensor (4a, 4b) arranged on the substrate, wherein the first and the second temperature sensor (4a, 4b) are designed as heatable temperature sensors (5a, 5b), which serve as both a heating element and as a sensor to measure the temperature, or as a first non-heatable temperature sensor (6a, 6b) to which a first heating element is assigned and as a second non-heatable temperature sensor to which a second heating element is assigned; - a feed unit, which, using a first signal, is designed to supply a first heating power to the first heatable temperature sensor or to the first heating element, said heating power being predefined during a calibration mode in which the flow of the medium is essentially brought to zero or held at zero, and, using a second signal, is designed to supply a second heating power to the second heatable temperature sensor or to the second heating element, said heating power being determined in the calibration mode in advance in such a way that, in the calibration mode, there is an essentially symmetrical temperature distribution over the two heatable temperature sensors (5a, 5b) or the two heating elements (7a, 7b); - an evaluation unit, which is designed to apply - during a measuring mode for the purpose of determining the flow of the medium - the first heating power determined during the calibration mode to the first heatable temperature sensor or the first heating element and to apply the second heating power determined during the calibration mode to the second heatable temperature sensor or the second heating element, and to determine a temperature difference (ΔT) between the first temperature sensor and the second temperature sensor and to determine, using the temperature difference (ΔT), a measured value that represents the flow of the medium. - a substrate; - a first and a second temperature sensor (4a, 4b) arranged on the substrate, wherein the first and the second temperature sensor (4a, 4b) are designed as heatable temperature sensors (5a, 5b), which serve as both a heating element and as a sensor to measure the temperature, or as a first non-heatable temperature sensor (6a, 6b) to which a first heating element is assigned and as a second non-heatable temperature sensor to which a second heating element is assigned; - a feed unit, which, using a first signal, is designed to supply a first heating power to the first heatable temperature sensor or to the first heating element, said heating power being predefined during a calibration mode in which the flow of the medium is essentially brought to zero or held at zero, and, using a second signal, is designed to supply a second heating power to the second heatable temperature sensor or to the second heating element, said heating power being determined in the calibration mode in advance in such a way that, in the calibration mode, there is an essentially symmetrical temperature distribution over the two heatable temperature sensors (5a, 5b) or the two heating elements (7a, 7b); - an evaluation unit, which is designed to apply - during a measuring mode for the purpose of determining the flow of the medium - the first heating power determined during the calibration mode to the first heatable temperature sensor or the first heating element and to apply the second heating power determined during the calibration mode to the second heatable temperature sensor or the second heating element, and to determine a temperature difference (ΔT) between the first temperature sensor and the second temperature sensor and to determine, using the temperature difference (ΔT), a measured value that represents the flow of the medium.