All depends on the offence, as recorded by the referee in his match report. Violent conduct carries a mandatory 3 match ban for the first offence in a season. This can be appealed against by the player's club. Ronaldo thus picked up a three match ban. If he is sent off a second time this season for violent conduct, he'll get a five match ban.
A straight red card for a "professional foul", denying a clear goalscoring opportunity, or "serious foul play" constitutes a one match ban. This can be appealed against by the player's club. Again though, if the player has already been dismissed this season, whatever that dismissal was for (including two yellow cards in the same game), the ban for subsequent red card will be longer.
If a player gets a red card as a result of two yellow cards in the same game, the ban will be one match, unless it's a second such red card, whereby it will be a longer ban. There is no appeal against a red card for two cautionable offences, though either of the cautions may be challenged at appeal.