准确计算CoreText高度的方法：

- (int)getAttributedStringHeightWithString:(NSAttributedString *)  string  WidthValue:(int) width
{
   int total_height = ;  

   CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)string);    //string 为要计算高度的NSAttributedString
   CGRect drawingRect = CGRectMake(, , width, );  //这里的高要设置足够大
   CGMutablePathRef path = CGPathCreateMutable();
   CGPathAddRect(path, NULL, drawingRect);
   CTFrameRef textFrame = CTFramesetterCreateFrame(framesetter,CFRangeMake(,), path, NULL);
   CGPathRelease(path);
   CFRelease(framesetter);  

   NSArray *linesArray = (NSArray *) CTFrameGetLines(textFrame);  

   CGPoint origins[[linesArray count]];
   CTFrameGetLineOrigins(textFrame, CFRangeMake(, ), origins);  

   int line_y = (int) origins[[linesArray count] -].y;  //最后一行line的原点y坐标  

   CGFloat ascent;
   CGFloat descent;
   CGFloat leading;  

   CTLineRef line = (CTLineRef) [linesArray objectAtIndex:[linesArray count]-];
   CTLineGetTypographicBounds(line, &ascent, &descent, &leading);  

   total_height =  - line_y + (int) descent +;    //+1为了纠正descent转换成int小数点后舍去的值  

   CFRelease(textFrame);  

   return total_height;  

}  

来自：http://blog.csdn.net/iunion/article/details/7925951