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Site-specific rainfall was recorded with four rain gauges (with gauge spacings of 1.02 km, 2.22 km, and 3.04 km) on a 250-ha farm in eastern Indiana over four growing seasons. Precipitation was aggregated by corn and soybean phenological phases to determine and compare spatial and temporal precipitation variability at this scale. The median absolute deviation among gauges, representing spatial precipitation variability, ranged from 0.25 to 1.73 mm/day. A reference year of phenological phases was constructed from crop growth literature and applied to on-farm historical precipitation data. The median absolute deviation of daily precipitation from the reference year, representing temporal (year-to-year) precipitation variability, ranged from 0.17 to 3.40 mm/day. Organization of yearly precipitation by phenological phase showed year-to-year (temporal) variability to be greater than spatial variability, over the same area, for most crop periods. Up to a distance of 3.04 km, median absolute deviation between gauges was less than 1 mm for most phases, which suggests that the required spacing for representing site-specific precipitation is 3.05 km or greater. The limited time scale and fixed orientations of the gauges restrict the applicability of the results to widespread areas. However, at least in this case, site-specific precipitation measurement is not necessary for a farm 250 ha or smaller.