Determining starch degradability is important because of its implicit relation to gut health, ruminal acidosis, energy availability, feed intake, and animal productivity. In vitro assays for protein and fiber degradability have been useful tools for ration formulation; however, analogous assessments of starch degradability have limited update. Our objective was to test how an enzymatic in vitro starch degradation assay compared with the in situ technique in terms of its ability to rank feeds based on their starch degradation rates. Samples of 19 livestock feeds were obtained from 4 feed mills and subjected to in vitro and in situ starch degradation analyses. Seven ruminally cannulated wethers on forage were used for the in situ procedure. In vitro starch degradation was assessed using an acetate buffer technique with modified enzymatic incubation times: amylase (AML) 5 min and amyloglucosidase (AMG) 10 min; AML 10 min and AMG 20 min; AML 15 min and AMG 30 min; AML 30 min and AMG 60 min; AML 45 min and AMG 90 min; and AML 60 min and AMG 120 min. In situ rates were determined using the Ørskov method and in vitro predicted rates calculated assuming exponential decay. Relationships were analyzed as a linear mixed-effects model with in situ degradation rate as the response variable and in vitro predicted degradation rate, initial free glucose, starch, crude protein, neutral detergent fiber (NDF), and fat content as fixed effects. Interactions between in vitro predicted degradation rate and the nutrient percentages were also included. Feed source was included as a random effect. In vitro predicted starch degradation rates ranged from 2.98% to 279%/h and in situ degradation rates ranged from 1.53% to 42.8%/h. A relationship between in vitro and in situ methods was observed when starch, fat, NDF, and initial free glucose content were accounted for. Interactions between in vitro predicted degradation rate and starch and NDF contents were also observed, suggesting that these nutrients may confound the relationship between in vitro and in situ starch degradation measurements. Removing the rapidly degradable starch fraction from in situ analysis calculations improved the strength of the relationship between in situ and in vitro starch degradation rate. This in vitro assay may prove more useful for determining relative rankings of starch degradation rates among different feedstuffs rather than serving as an alternative to the in situ method. Additional investigation into assay repeatability and comparisons with true in vivo estimations of starch degradation are needed to confirm the usefulness of this in vitro screening technique.