<!-- ckeditor/config.js -->
function e(id){
 return document.getElementById(id)
} 

function getWindowHeight() {
 var elem = (document.compatMode === "CSS1Compat") ? document.documentElement : document.body;
 return elem.clientHeight;
}

function calculateOffsetTop(element, opt_top) {
 var top = opt_top || null;
 var offset = 0;
 for(var elem = element; elem && elem != opt_top; elem = elem.offsetParent) {
  offset += elem.offsetTop;
 }
 
 return offset;
}

function dynamicEditorHeight() {
 var window_h = getWindowHeight();
 var resizer_height = window_h - calculateOffsetTop(e(document.forms[0].id));
 var title_field_h = e("content_title").offsetHeight || 20;
 var toolbar_h = 62; // double line toolbar
 var btm_grab_div_h = 21;
 var submit_btn_h = (document.forms[0].commit) ? document.forms[0].commit.offsetHeight : 0;
 var padding_h = 60;
 resizer_height -= (title_field_h + toolbar_h + btm_grab_div_h + submit_btn_h + padding_h + 50); // extra buffer to avoid window scrollbar
 return(resizer_height);
}
 
CKEDITOR.editorConfig = function( config ) { 
 config.height = dynamicEditorHeight();
};

<!-- application.js -->
function e(id){
 return document.getElementById(id)
} 

function getWindowHeight() {
 var elem = (document.compatMode === "CSS1Compat") ? document.documentElement : document.body;
 return elem.clientHeight;
}

function calculateOffsetTop(element, opt_top) {
 var top = opt_top || null;
 var offset = 0;
 for(var elem = element; elem && elem != opt_top; elem = elem.offsetParent) {
  offset += elem.offsetTop;
 }
 
 return offset;
}

function dynamicEditorHeight() {
 var window_h = getWindowHeight();
 var resizer_height = window_h - calculateOffsetTop(e(document.forms[0].id));
 var title_field_h = e("content_title").offsetHeight || 20;
 var toolbar_h = 62; // double line toolbar
 var btm_grab_div_h = 21;
 var submit_btn_h = (document.forms[0].commit) ? document.forms[0].commit.offsetHeight : 0;
 var padding_h = 60;
 resizer_height -= (title_field_h + toolbar_h + btm_grab_div_h + submit_btn_h + padding_h + 50); // extra buffer to avoid window scrollbar
 return(resizer_height);
}
 
CKEDITOR.editorConfig = function( config ) { 
 config.height = dynamicEditorHeight();
};

CKEditor Dynamic Resize

JavaScript