As a global measure of precision, item response theory (IRT) estimated reliability is derived for four coefficients (Cronbach's α, Feldt‐Raju, stratified α, and marginal reliability). Models with different underlying assumptions concerning test‐part similarity are discussed. A detailed computational example is presented for the targeted coefficients. A comparison of the IRT model‐derived coefficients is made and the impact of varying ability distributions is evaluated. The advantages of IRT‐derived reliability coefficients for problems such as automated test form assembly and vertical scaling are discussed.