Pressurized gas drives explosive volcanic eruptions. Existing models can predict the amount and pressure of gas in erupting magma, but application and testing of such models is currently limited by the accuracy of input parameters from natural systems. Here, we present a new methodology, based on a novel integration of 1) high‐speed imaging and 2) shock‐tube modeling of volcanic activity in order to derive estimates of sub‐second variations in the pressure, mass, and volume of gas that drive the dynamics of unsteady eruptions. First, we validate the method against laboratory‐scale shock‐tube experiments. Having validated the method we then apply it to observations of eruptions at Stromboli volcano (Italy). Finally, we use those results for a parametric study of the weight of input parameters on final outputs. We conclude that Strombolian explosions, with durations of seconds, result from discrete releases of gas with mass and pressure in the 4–714 kg and 0.10–0.56 MPa range, respectively, and which occupy the volcano conduit to a depth of 4–190 m. These variations are present both among and within individual explosions.