# How To: Convert Area into Acres

## Summary

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

## 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 article 24646, '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`

2. 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.`

3. 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
4. In ArcGIS Desktop at version 10, the Calculate Geometry option in the Attribute Table can also be used.

a) 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.
b) Add a field named Acres to the attribute table, as described above.
c) Right-click the Acres field, and run the Calculate Geometry utility using the data frame's coordinate system.