First, estimate your cooling hours by clicking on your location.  Then, click the 'Accept' button to use this value in the calculator.  You may also type in your own estimate. 
The contour lines represent approximate hours to run a correctly sized AC unit.  Shaded areas apply to Evaporative (swamp) coolers.
Selected Value                               Help
Map of Summer Cooling Load Hours
Reprinted from pages 16 and 17 of the ARI Unitary Directory, August 1, 1992 - January 31, 1993
Courtesy of the Air-Conditioning and Refrigeration Institute, ARI.