Buffer Area Miscalculation

[NicoleFreeman]

I have 12 sites ontop of a landuse/landcover file.  I buffered a region around each site, used extract by mask to pull out the area contained inside the buffer, and used that to look at which types of landuse are in each buffer region.  The problem is that the actual area buffered is not the same as my calculated area of a circle.  (Ex: 14.7 square km instead of 50.9 square km.)  Any ideas why this is happening and how I can fix it?

[NicoleFreeman]

For at least one of the 12 maps giving me trouble, it was a user error.  I believe that when I put in the linear distance, I clicked the wrong unit of measurement or typed a wrong number.  I buffered everything again with more care and my actual area matched the estimates.  I'm not sure at this point the same holds true for all maps, but I wanted to post a solution for anyone else that might encounter this problem.