Based on published and new data for explosive events at Stromboli (Italy), we propose an empirical relation that links mass discharge rate (MDR) and at-vent gas jet velocity (G_v). We use 65 simultaneous measurements of MDR and G_v and find two trends in both the cross-correlation and rank order statistics. Cross-correlation gives a power law relation: M D R =10^{(0.015 G_v+2.434 )} kg/s, R² = 0.81, and applies to ash-dominated emissions. Combining this relation with the conservation of mass equation allows at-vent plume density and/or vent area to be derived from MDR = G_vρA, ρ being plume density and A being vent cross-sectional area. We find that while a vent radius of 2 m and plume density of 0.35 kg/m³ fits with the "normal" activity at Stromboli, a 290 × 2.5 m vent area likely feeds a 10 kg/m³ jet during paroxysmal activity. Initial tests on available data shows promise in extending the correlation beyond Stromboli and/or to events with higher MDR (> 10⁷ kg/s). However, the exact relation will depend on magma composition, temperature and volatile content, as well as conduit radius and vent overpressure.