# Use Grid Math and Grid Volume on grids with different grid geometry in Surfer

Do you need to perform mathematical calculations using one or more grid files? Or determine the volume between an upper and lower grid surface? These calculations were always possible in Surfer but only between grid files with identical geometry – a rarity in the real world. Surfer now allows users to perform these calculations with grids of different sizes and different X and Y value extents!

The Grid Math and Grid Volume tools work just the same as they have in previous versions, but now you have the option to align the grids by XY extents or grid nodes.

See the steps to perform Grid Math or Grid Volume on grids with differing geometry below:

- Click
**Grids | Calculate | Math**or**Grids | Calculate | Volume.** - Import grids in either dialog as usual. For more information about fields not covered here, see one of the following resources:
- In the
*Align grids using*dropdown, select:*Node position*if the grids have the same number of rows, columns, and spacing.*XY Coordinates*if the grids do not have the same number of rows, columns, or spacing.

- Choose the grid for the
*Master grid (for geometry)*field. This field is used for grids that are not in the same coordinate system.- If
*Align grids using*is set to*XY coordinates*and all grids are referenced but in a different coordinate system, the resulting grid file uses the master grid's coordinate system. If an input grid files is not referenced but another grid file is referenced, Surfer displays a warning about mixing referenced and unreferenced grid files. Selecting*Yes*continues with the math function operation, but none of the other grids will be projected to the master grid's coordinate system. -
If the grids are in the same coordinate system, selecting

*Yes*will perform the math as expected. However, if a grid is not referenced and not in the same coordinate system, select*No*at the warning to cancel the math function operation and return to the**Grid Math**or**Grid Volume**dialog. Select different grid files with referenced or matching coordinate systems or use the**Grids | Edit | Assign Coordinate System**to change the coordinate system of one or more of the grid files.

- If
- Name the new grid, choose a saving location, and click
*OK.*The new grid will be created.

**Video Tutorial:**

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