boundingRectWithSize

 ChatMessage *message = [chatMessages objectAtIndex:indexPath.row];
        CGFloat topMargin = (indexPath.row == 0) ? 18 : 0;

        CGRect stringRect = [message.text boundingRectWithSize:CGSizeMake(200, MAXFLOAT)
                                              options:NSStringDrawingUsesLineFragmentOrigin
                                           attributes:@{ NSFontAttributeName : [UIFont fontWithName:CHAT_CELL_FONT size:14] }
                                              context:nil];
        CGSize stringSize = CGRectIntegral(stringRect).size;

        CGFloat bottomMargin = [self isMessageHasTail:indexPath.row] ? 30 : 20;
		return stringSize.height + bottomMargin + topMargin;