Determining in-place concrete strengths is particularly important for the seismic evaluation of existing buildings. Underestimating the concrete strength in a seismic rehabilitation design by adopting a lower-bound estimate of the in-place concrete strength can undervalue component resistances, potentially triggering inappropriate rehabilitation solutions. The objective of this article is to review assessment requirements and guidelines and identify ways of setting core sampling requirements appropriate for seismic evaluation. Recommendations are based on a review of statistical methods to select sample size for an acceptable error level and assessment of outlier data.