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This paper aimed at proposing a simple criterion for estimates on volume sizing for detention reservoir considering different return periods and occupational scenarios, based on Fortaleza city's IDF relationship (intensity-duration-frequency) of critical rainfall events, presenting mathematical regression formulations linking those variables. A theoretical background was made to support problems related to urbanization in the natural hydrologic cycle, and relating all needed variables for the expeditious sizing. Thus, the detention reservoir was detailed, with its characteristics and places where it can be applied and its pre-sizing method being explained. On the methodology, the envelope curve method was adopted to estimate the exceeding volume which was used for sizing the detention reservoir. Software MATLAB® was used to solve the resulting equation, yielding 60 durations and 60 water line heights, from a combination of 10 occupational rates and 6 return periods. For example, for a contribution area of 40 hectares, impervious area of 70% and return period of 25 years, the detention reservoir needs the capacity of about 18.000 m2 to meet the assumed pre-sizing flow rate. This paper's result showed up to be potentially useful for the urban drainage design planning phase in several areas in Fortaleza city, in which the occupational rate and the return period can be varied according to the designer's will. In addition to that, this method can be adapted to other areas once their IDF curve is available. [ABSTRACT FROM AUTHOR]