Since even small amounts of tephra fall can have a significant negative impact on infrastructure, a rapid estimate of the eruptive mass of magma, which is one of the most important indicators of the scale of eruption, is required. Shinmoedake volcano, part of the Kirishima volcanoes, Japan, began erupting on 19 January 2011 after a dormant period of 300 years. Sub-plinian eruptions occurred on 26-27 January, followed by vulcanian eruptions and eruptions of ash fall thereafter. Here, we report the results of a preliminary study that sought to estimate the eruptive mass and the distribution of ash fall based on observations of tephra fall within 2 weeks of an eruption at Shinmoedake. In cooperation with municipal authorities, we observed temporal changes in the amounts of ash erupted during volcanic activity at Shinmoedake volcano from 24 February 2011 to 29 February 2012. Observations were made at 35 sites in five municipalities (Miyakonojo City, Takaharu Town, Kirishima City, Kobayashi City, and Ebino City). The observations enabled estimates of the eruptive masses of ash from seven eruptive events. The eruptive masses are between 1×10^6kg and 2×10^8kg, with the largest being the eruption of 13 March 2011. We found positive correlations between (1) the eruptive mass and the height of volcanic cloud determined by radar echo and between (2) the eruptive mass and the height of cloud that reported by the Japan Meteorological Agency. The former correlation is consistent with a relatively well-known geophysical relationship between the maximum height of a convection current and the amount of thermal output pulse. The empirical correlation may allow us to easily and rapidly estimate the eruptive mass from the observed height of the volcanic cloud top.