For calculating the volume, always two sets of surface data are required.

- Initial Level: Original Ground Level (OGL) (survey data)
- Final Level: Proposed/Designed Level (estimate) or Formation Level (survey data)

Let us consider the following example where the survey data is converted into grid levels as shown below and the final level is 20 meters.

For each grid line, cross sections should be drawn, and area of cutting and area of filling should be determined for each section. These areas become the basis of volume calculation using section method.

**Finding the Intersection Point:**
When a section is drawn using two sets of grid levels, and if the section lines are intersecting, then we have to find the intersection point for future calculations.

In the above example, we need to find intersection at point B i.e., distance between A and B.
AB= Horizontal distance between A and C * [Level difference at point A / (Level difference at Point A + Level difference at Point B)]
AB = 5 * [1 / (1+2)] = 1.67

**Area Calculation:**
Once the sections are drawn and intersection points are determined, then we can find the area of each section using any of the following methods:

- Trapezoidal rule
- Nett Area method
- Simpsons 1/3rd rule

Volume Calculation Methods Section - Trapezoidal Rule (End Area)