If a player is sent off, it is a matter of fact the player will be suspended 7 days after the date of the game, as set out by The FA in the Discipline Handbook.

The length of ban depends on the reason for the dismissal as determined by the referee: 

Serious Foul Play

3 match suspension

Violent Conduct

3 match suspension

Spitting at an opponent

6 match suspension

Denies an obvious goal scoring opportunity by an offence punishable by a free kick or penalty kick

1 match suspension

Denying an obvious goal scoring opportunity by deliberately handling the ball

1 match suspension

Use of offensive, or insulting or abusive language

2 match suspension

Receiving a second caution in a match

1 match suspension

If you have already been sent off during the current season, you will receive additional match(es) depending on the number of times you have previously been shown a red card.

You can find out more about sanctions for red cards, including the fines for each offence, in The FA's Essential Guidance for Clubs at Step 5 and Below.