You can calculate the volume or area between contour levels easily in Surfer v21 and higher either in the user interface or via automation.  The Contour Vol/Area tool allows you to calculate the volume and area above contour lines, below contour lines, and in between contour lines. For example, find the volume under a contour value of 50. Or, find the total area between contour values of 50 and 100. 

For performing these steps in automation, see: Calculate the volume or area between contour levels with Surfer automation

To calculate the volumes and areas between contour levels, follow these steps:

1. Click Grids | Calculate | Contour Vol/Area in the ribbon. 
   
   
2. In the Input Grid field, either click over None to select an open grid file, or click Browse to browse to a grid file. 
3. Set the Minimum Contour, Maximum Contour, and Contour Interval fields to your desired settings. 
   
   
   • If you chose to select an open grid from the dropdown, Surfer will automatically use the Minimum Contour, Maximum Contour, and Contour Interval that are set in the Property Manager on the Levels tab. These values can be changed by typing in a new value.
   • If you chose to select a new grid via Browse, Surfer will automatically apply the default Minimum Contour, Maximum Contour, and Contour Interval that you would see upon importing the grid as a Contour map. These values can be changed by typing in a new value.
     
4. Click OK. Review the information in the report. Save the report by clicking File | Save if desired. 

Surfer will output the Grid Contour Vol/Area report. This report contains the following information: 

• The Grid Input section displays the grid file, minimum contour value, maximum contour value, and interval used to generate the report. 
  
  
• The Contour Areas section lists each contour value and the associated data for the following:
  • Planar Area Above Contour
  • Planar Area Below Contour
  • Surface Area Above Contour
  • Surface Area Below Contour
  • Surface Area Between Contour 
    
    
    
    
• The Contour Volumes section lists each contour value and the associated data for the following:
  • Volume Above Contour
  • Volume Below Contour
  • Volume Between Contour 
    
    

1. Click Grids| Calculate | Volume.
2. In the Grid Volume dialog, click Browse.
3. In the Open Grid dialog, select your grid file and click Open.
4. Set the grid file as the Upper Surface | Grid File and the Z level of the first contour as the Lower Surface (Constant Z = ).
5. Click OK.
6. Record the Volumes | Cut & Fill Volumes | Positive Volume [Cut] value or Areas | Planar Areas | Positive Planar Area [cut] value for areas from the report.
7. Repeat steps 1 - 6, generating a second report with the same grid file as the Upper Surface and the Z level of the second contour as the Lower Surface.
8. Subtract the second value from the first value to get the volume or area between the two contours.

Updated November, 2021