**Based on documentation from ENVI software the values should be between -1 and 1, [see here][1]**

The Enhanced Vegetation Index (EVI) is an algebraic equation of:

    EVI = G X ((NIR - RED)/ (NIR + (C1 x RED)-(C2 x BLUE) + L))

Where NIR is the value of the near infrared band, RED is the value of the red band, BLUE is the value of the blue band, (all three bands are atmospherically-corrected), L is the canopy background adjustment. Additionally G is the gain factor, C1 and C2 are the coefficients of the aerosol resistance term. In ENVI software G = 2.5, C1 = 6, C2 = 7.5, and L = 1. 

For more background information on EVI go to the Wikipedia page [here][2] or for a thread on how to implement the equation manually [go here][3].


  [1]: http://www.harrisgeospatial.com/Learn/Whitepapers/TabId/2359/ArtMID/10212/ArticleID/16162/Vegetation-Analysis-Using-Vegetation-Indices-in-ENVI.aspx
  [2]: https://en.wikipedia.org/wiki/Enhanced_vegetation_index#Two-band_EVI
  [3]: https://geonet.esri.com/thread/69192