How to measure rape precisely has been an important topic in feminist research on violence against women since the 1980s. The norm in contemporary studies is to use behaviourally specific questions identifying specific acts that are judicially considered rape to measure the phenomenon, but some studies also use broad single-item questions. In the present study, a survey experiment was conducted among adolescents from Oslo, the capital of Norway, to investigate discrepancies in the prevalence of rape using three different measures and to determine whether the method of measurement differentially affected the prevalence rates according to a range of individual background characteristics. The broad single-item question returned the lowest prevalence of rape, with rates of 5% among girls and 1% among boys. Excluding an item on involuntary incapacitated sex, the prevalence rates when behaviourally specific questions were asked were 9% among girls and 2% among boys; the rates were 14% and 3% (respectively) when this item was included. No significant interactions were identified in logistic regression analyses between the rape instruments and the different background characteristics, which indicates that the relative difference in prevalence rates between groups did not differ according to the chosen method when measuring rape. We use the results from the study to discuss what would be a ‘good enough’ measure of rape among adolescents.