Work out contour volume (prismoidal) instantly with clear inputs, formula shown and shareable results.
The prismoidal formula, h/3 x (A1 + 4A2 + A3), fits a second order surface through three equally spaced contour areas and is exact for a prismoid. Average end areas treats each pair as a wedge and always over-estimates where the shape is convex, so the difference between the two is the prismoidal correction.
Prismoidal formula
V = h/3 x (A1 + 4 A2 + A3), for two equal intervals h
Average end areas
V = h x [(A1 + A2)/2 + (A2 + A3)/2]
V = h/3 x (A1 + 4 A2 + A3), for two equal intervals h. The prismoidal formula, h/3 x (A1 + 4A2 + A3), fits a second order surface through three equally spaced contour areas and is exact for a prismoid.
On steep or rapidly changing ground and on large volumes, where the correction can exceed two percent. For flat sites with close contours the two methods agree closely.
This calculator takes 4 inputs: Area of the lower contour, Area of the middle contour, Area of the upper contour, Contour interval. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.