The 1815 eruption of Mount Tambora (Sumbawa Island, Indonesia), largest known explosive eruption in recorded history, was cataclysmic. It was responsible for a strong short-term global atmospheric cooling the following year, known as "the year without a summer". To evaluate the climatic impact, an accurate quantification of volatile elements degassed during this eruption is crucial. In this study, we re- evaluate the atmospheric release of sulfur, chlorine and fluorine during the 1815 eruption using the petrological approach based on plagioclase-hosted melt inclusions. The pre-eruptive (melt inclusions) and post-eruptive (matrix glass) volatile element concentrations of the magma are measured by electron microprobe. We discuss three different outgassing scenarios and conclude that 147 ± 17 Tg of SO₂, 49 ± 5 Tg of Cl and 20 ± 2 Tg of F were degassed during the eruption, considering closed system ascent and degassing. The SO₂ results take into account the dissolution of sulfides which are present in melt inclusions and plagioclase crystals but not in matrix glasses. Our new estimates are higher than previous estimations from petrological methods or derived from ice cores but are consistent with atmospheric optical depth observations from 1816. The 1815 eruption of Tambora ranks in first place in terms of volcanic SO₂ emission in the last 2000 years, higher than the 1257 Samalas eruption (Lombok Island, Indonesia) if equal methodologies are applied. These estimates remain nonetheless minima as they do not account for the possible additional contribution of a pre-existing gas phase in the magma reservoir.