Infrared thermometers (IRTS) are a convenient method of measuring surface temperatures of crop canopies. The effect of calibration method and size of the crop canopy area being viewed on measured canopy temperature were evaluated under field conditions. A linear equation with individual coefficients for each of eighteen IRTs estimated the relative temperature (TR), which is the target minus the head temperature of the IRT, more closely than using the manufacturer's single fifth order polynomial calibration equation for all IRTs over a TR range of +/-20 C. Differences in TR were compared among a black body standard (TRBB) and those estimated by either the field (TRFC) or manufacturer (TRMC) calibrations indicated that TRBB minus TRMC differences and the TRFC minus TRMC differences were significantly greater than zero. Defining a maximum TR difference between TRFC - TRMC of 0.5 C as acceptable, all IRTs had some unacceptable differences over a TR range of +/-7 C. Canopy temperatures, measured under clear sky conditions, that were estimated by scanning the canopy compared with viewing a fixed canopy area were small, (0.3 C for a 30 C canopy temperature level) but significantly different. Canopy temperatures on the south side of east-west rows were higher than on the north side.