another CT size try

gistfile1.m

- (CGFloat)getContentHeight
{
    CTFramesetterRef tmpFrameSetter = CTFramesetterCreateWithAttributedString((__bridge CFAttributedStringRef)_body);
    int textLength = [_body length];
    
    CFRange range;
    CGFloat maxWidth    = self.width;
    CGFloat maxHeight   = CGFLOAT_MAX;
    CGSize constraint   = CGSizeMake(maxWidth, maxHeight);
    CGSize contentSize  = CTFramesetterSuggestFrameSizeWithConstraints(tmpFrameSetter, CFRangeMake(0, textLength), nil, constraint, &range);
    
    return contentSize.height;
}