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# How To: Convert Area into Acres

## Summary

Instructions provided describe how to convert values in the area field into acres.

```Note:
This article pertains to ArcGIS versions 8.x and 9.x. Later versions of ArcGIS may contain different functionality, as well as different names and locations for menus, commands and geoprocessing tools.```

## Procedure

If the data is stored in a geographic coordinate system, which uses units in decimal degrees, the data must be projected to a projected coordinate system which uses a linear unit of measure like meters. Because decimal degrees are angles, an area calculation based on decimal degrees cannot be converted to a usable unit of measurement.

Refer to the article: How to select a suitable map projection or coordinate system  in the Related Information section for more information about selecting an appropriate projected coordinate system for data.

1. Calculate area of polygon features.
```Note:
Area for polygons in a geodatabase feature class is calculated automatically by the software```
1. Create a new field named Acres in the attribute table.
```Note:
Define the new field as DOUBLE. The precision is the length of the field, and the scale represents the number of decimal places. A precision of 18, and scale of 3, for units of feet or meters in a projected coordinate system should accommodate the values to be stored in this field.```
1. Calculate the value for acres for the field by applying the appropriate conversion, such as square feet to acres or square meters to acres.
Conversion factors:
• square feet * 0.000022956 = acres
• square meters * 0.0002471054 = acres
2. In ArcGIS Desktop at version 10, the Calculate Geometry option in the Attribute Table can also be used.
1. If the data are in a geographic coordinate system, set the coordinate system of the ArcMap data frame to a projected coordinate system. Go to View > Data Frame Properties > Coordinate System tab > Predefined > Projected Coordinate Systems and select a suitable coordinate system for the area in which the data is located.
2. Add a field named Acres to the attribute table, as described above.
3. Right-click the Acres field, and run the Calculate Geometry utility using the data frame's coordinate system.