<PAGE>
 
                                                                      EXHIBIT 11

              CHAMPION INTERNATIONAL CORPORATION AND SUBSIDIARIES

          Calculation of Primary Earnings (Loss) Per Common Share and
          Fully Diluted Earnings (Loss) Per Common Share (unaudited)
                       (in thousands, except per share)


<TABLE> 
<CAPTION> 
                                                       Six Months Ended          Three Months Ended
                                                    ----------------------     ----------------------
                                                           June 30,                   June 30,
                                                    ----------------------     ----------------------
                                                       1997        1996           1997       1996
                                                    ----------  ----------     ----------  ----------
<S>                                                 <C>         <C>            <C>         <C>  
Primary earnings (loss) per common share:           
  Net Income (Loss) Applicable to Common Stock      $ (48,441)  $   99,201     $ (11,358)  $   15,552
                                                    ==========  ==========     ==========  ==========
                                                    
  Average number of common shares outstanding          95,625       95,508        95,659       95,511
                                                    ==========  ==========     ==========  ==========
                                                    
  Per share                                            ($0.51)       $1.04        ($0.12)       $0.16
                                                    ==========  ==========     ==========  ==========
                                                    
Fully diluted earnings (loss) per common share:     
  Net Income (Loss) Applicable to Common Stock      $ (48,441)  $   99,201     $ (11,358)  $   15,552
                                                    
  Add income effect, assuming conversion of         
    dilutive convertible securities                       ---          ---           ---          ---
                                                    ----------  ----------     ----------  ----------
  Net income (loss) on a fully diluted basis        $ (48,441)  $   99,201     $ (11,358)   $  15,552
                                                    ==========  ==========     ==========  ==========
                                                    
  Average number of common shares outstanding          95,625       95,508        95,659       95,511
                                                    
  Add common share effect, assuming conversion      
    of dilutive convertible securities                    ---          ---           ---          ---
                                                    ----------  ----------     ----------  ----------
  Average number of common shares outstanding       
    on a fully diluted basis                           95,625       95,508        95,659       95,511
                                                    ==========  ==========     ==========  ==========
                                                    
  Per share                                            ($0.51)       $1.04        ($0.12)       $0.16
                                                    ==========  ==========     ==========  ==========
</TABLE> 

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NOTE:

(1) The computation of fully diluted earnings per common share assumes that the
    average number of common shares outstanding during the period is increased
    by the conversion of securities having a dilutive effect, and that net
    income applicable to common stock is increased by dividends and after-tax
    interest on such securities.