Abstract: Described herein are systems and methods for determining the volume of liquid and/or solids present in a vessel by flowing gas to or from an accumulator vessel and using the ideal gas law to determine the volume of gas (e.g., void space) present in the vessel. Advantageously, the described systems and methods and nonintrusive and may be useful for applications in which the level of liquid/solids in the vessel are unstable or where traditional volumetric measurements would interfere with internal processes, such as agitation.