Two experiments report on the construction of the Sense of Agency Rating Scale (SOARS), a new measure for quantifying alterations to agency. In Experiment 1, 370 participants completed a preliminary version of the scale following hypnosis. Factor analysis revealed two underlying factors: Involuntariness and Effortlessness. In Experiment 2, this two factor structure was confirmed in a sample of 113 low, medium and high hypnotisable participants. The two factors, Involuntariness and Effortlessness, correlated significantly with hypnotisability and pass rates for ideomotor, challenge and cognitive items. Twelve week test-retest correlations showed that Involuntariness was highly stable, but Effortlessness only moderately stable. Analysis of the combined datasets from Experiments 1 and 2 showed both SOARS scores were significantly related to the derived factors of Woody, Barnier, and McConkey's (2005) 4-factor model of hypnotisability. This scale clarifies conceptual confusion around agentive action and provides empirical support for a multifactorial account of sense of agency.