Long Base (B) of the base trapezoid. Short Base (b) of the base trapezoid. 7 juin 2022 · The Trapezoid Volume (Rectangular) calculator computes the volume of trapezoid volume shape based on the dimensions: INSTRUCTIONS: Choose units and enter the following: (a) Width of Top (b) Length of Top (A) Width of Bottom (B) Length of Bottom (h) Height between Top and Bottom Trapezoid Volume (V): The calculator returns the volume in cubic met.