This survey assessed the knowledge of the "Guidance for prescribing exercise" issued by the American College of Sports Medicine (ACSM) in 2011 among certified exercise professionals. A sample of 1,808 certified exercise professionals (66.70% women, mean (± SD) age = 38.28 ± 12.56 years) responded to electronic invitations. The 11-question online questionnaire assessed knowledge of the recommended frequency, duration, and intensity ranges in terms of heart rate, metabolic equivalents, and ratings of perceived exertion. Respondents had 7.45 ± 8.07 years of work experience and represented all 50 U.S. states. On average, participants answered 42.87 ± 1.69% of the questions correctly. Gender, age, and years of professional experience were not associated with overall knowledge of the guidelines. Likewise, having 1, 2, or 3+ certifications made no difference in overall knowledge. However, there were significant differences between levels of education (F = 7.12, p < 0.001), from 38.72 ± 1.62% for "some college" to 47.01 ± 1.71% for "doctorate." There were also significant differences by primary job role (F = 3.45, p < 0.001) but no category exceeded 49% (e.g., personal trainers: 40.59 ± 1.66%; clinical exercise physiologists: 44.18 ± 1.70%). The respondents rated their knowledge of the exercise prescription guidelines as 7.01 ± 1.69 of 10 but rated the level of knowledge necessary to practice safely and effectively as 8.32 ± 1.64 (t = 28.60, p < 0.001). This survey, the first at this scale to investigate the knowledge of exercise prescription guidelines among certified exercise professionals, showed that there is room for improvement, considering that the average score was below 50%.