We suggest that the Tambora 1815 eruption was smaller than previously thought, yielding 30--33 km3 of magma. Valuable insight into the eruption is gained by comparing it to the much smaller 1991 Pinatubo event, which had a similar eruption style and rate. By measuring pre- and post-eruption sulfur concentrations in 1815 ejecta, we estimate that Tambora released 53--58 Tg (5.3--5.8 ¿ 1013 g) of SO2 within a period of about 24 hours on 10--11 April, 1815. This was sufficient to generate between 93 and 118 Tg of stratospheric sulfate aerosols. A value within this range, distributed globally, agrees well with estimates of aerosol mass from ice-core acidity and the radiative impact of the eruption. In contrast to other recent explosive arc eruptions, the Tambora ejecta retain a record of the sulfur mass released, with no excess sulfur.