Code to get full size avatar and not thumbnail

Ok this might be kinda a silly question I have for Patrick. I have setup a custom sidebar login widget via this awesome tutorial: https://premium.wpmudev.org/blog/wordpress-login-page-sidebar-login/

Everything is working fine, but I just cant get the full size Avatar instead of the thumb. I know I can adjust size by increasing the number, bet then it gets real ugly up scaling a thumbnail.

So what correct code do I need to set instead of this:
echo get_member_avatar( $current_user->ID, 250 );