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.

Using Automation

Follow the instructions in this knowledge base article: How can I calculate the volume or area between contours with Surfer automation?. 

Updated November 7, 2018