Engineering calculator reviewed for preliminary design use · Last updated: March 2026
Calculate tank draining time using Torricelli's theorem from tank cross-section area, orifice area, and liquid head. Apply to batch operation scheduling, tank cleaning, and emergency drain planning.
Tank Draining Time Calculator (Torricelli's Theorem)
Calculates the time required to drain a tank through a bottom or side orifice/nozzle. Based on Torricelli's theorem (v = √(2gh)), the calculation accounts for discharge coefficient, orifice area, and initial/final liquid level.
Torricelli's theorem assumes inviscid, incompressible fluid with a free surface. It also assumes the tank cross-section is much larger than the outlet orifice. A discharge coefficient (0.6-0.65) corrects for real fluid effects.
Why does draining slow down as the tank empties?
The driving force is the hydrostatic head (liquid height above the outlet). As the liquid level drops, the head decreases, the exit velocity decreases, and the flow rate decreases — causing the draining to slow exponentially.
These results are preliminary estimates for screening-level design use. They do not replace detailed engineering, code compliance verification, or vendor-certified calculations.