A method has been developed in order to determine the in-plane non-uniformity of drying of wet paper samples dried by an air flow. The surface temperature of the samples, recorded by an infrared camera, is used to determine a mean drying time and the local drying time of each pixel. Based on the initial dryness and the mean drying time, a mean drying rate can be obtained, and furthermore, the drying time of each pixel can be presented as a 2-dimensional map. Apart from conventional statistical information on the variation in drying time, the map also gives information regarding the size and shape of the drying non-uniformity. The pressure drop over the sample and the air flow rate through the sample were used to calculate a flow resistance as a function of grammage. Laboratory sheets with grammages between 15 and 45 g/m2, made from an unrefined bleached chemical hardwood pulp, were analysed. A considerable variation in local drying time was observed, despite their anticipated uniform formation. The mean drying time increased linearly with increasing grammages, thus the mean drying rate was not dependent on grammage. The flow resistance of the sheets increased with increasing grammage. The air flow rate through the sheet appeared not to be critical for the drying rate at the given experimental conditions.