<PAGE>
 
                                                                      EXHIBIT 11

               CHAMPION INTERNATIONAL CORPORATION AND SUBSIDIARIES

           Calculation of Basic Earnings (Loss) Per Common Share and
             Diluted Earnings (Loss) Per Common Share (unaudited)
                        (in millions, except per share)


<TABLE> 
<CAPTION> 
                                                             Three Months Ended     
                                                                 March 31,          
                                                         ---------------------------
                                                          1998               1997   
                                                         ----------      -----------
<S>                                                     <C>             <C> 
Basic earnings (loss) per common share:                                             
  Net income (loss) applicable to common stock           $   19.0        $   (37.1) 
                                                         ==========      ===========
                                                                                    
                                                                                    
  Average number of common shares outstanding                96.1             95.6  
                                                         ==========      ===========   
                                                                                    
                                                                                    
  Basic earnings (loss) per share                        $  .20          $   (.39) 
                                                         ==========      ===========  
                                                                                    
                                                                                    
Diluted earnings (loss) per common share: (1)                                       
  Net income (loss) applicable to common stock           $   19.0        $   (37.1) 
                                                                                    
  Add income effect, assuming conversion of                                         
    potentially dilutive securities                           ___              ___  
                                                         ----------      -----------
                                                                                    
  Net income (loss) on a diluted basis                   $   19.0        $   (37.1) 
                                                         ==========      ===========
                                                                                    
                                                                                    
  Average number of common shares outstanding                96.1             95.6  
                                                                                    
  Add common share effect, assuming conversion                                      
    of potentially dilutive securities                         .9              ___  
                                                         ----------      -----------
  Average number of common shares outstanding                                       
    on a diluted basis                                       97.0             95.6  
                                                         ==========      ===========
                                                                                    
                                                                                    
  Diluted earnings (loss) per share                      $    .20        $    (.39) 
                                                         ==========      ===========
</TABLE> 
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NOTE:

(1)   The computation of diluted earnings per share assumes that the average
      number of common shares outstanding during the period is increased by
      dilutive common share equivalents and 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.