HOW TO

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.

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.

- Calculate area of polygon features.

Note:Area for polygons in a geodatabase feature class is calculated automatically by the software

- 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.

- 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

- In ArcGIS Desktop at version 10, the Calculate Geometry option in the Attribute Table can also be used.
- 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. - Add a field named
**Acres**to the attribute table, as described above. - Right-click the
**Acres**field, and run the**Calculate Geometry**utility using the data frame's coordinate system.

- 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

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