How to calculate the concrete quantity of a trapezoidal footing? An Isolated footing area may be in rectangular or square shape. We have explained the process for both shapes. First, We have to calculate the below rectangular part separated by the dotted line (refer the diagram), using rectangular area formula. Don’t forget to check out Basic Surface Area Formulas. For rectangular, the Area = A x B For Square, the Area = A 2 (assuming A=B) Check out different types of Trapezoid Geometry. Trapezoidal Footing Formula with drawing Trapezoidal Footing Volume , V = h/3 (A1+A2+√(A1 x A2)) Where, h – Height of trapezoidal (refer the diagram) A1 – Area of the lower shape A2 – Area of the upper shape