The UFC uses a '10-point must scoring system', which means that each round must have a winner, with that fighter being given 10 points, and the loser being given nine. The exception to that is in the case of a particularly dominant round by a fighter, where their opponent can sometimes be given just eight points.
So what criteria is considered when scoring fights in the UFC?
Rounds are judged on: effective striking/grappling, then effective aggressiveness and finally Octagon control.
Regarding effective striking, judges are looking for fight-altering strikes, as opposed to strikes that remind your opponent you're there. For example, leg and body kicks may not often result in knockouts, but they can certainly damage a fighter over the course of a bout, whereas timid strikes in a clinch are unlikely to significantly affect an opponent, and won't be rewarded highly.
Grappling is similar. Taking an opponent down alone isn't enough to be classed as 'effective', particularly if the opponent bounces back straight back to their feet. But the ability to move into an advantageous position on the ground, land strikes or perhaps attempt a submission will all be looked upon favourably.
Aggressiveness relates to how much pressure a fighter puts another under. Merely chasing an opponent around the cage wouldn't count as effective aggressiveness, but being able to use that pressure to launch strikes and takedowns would.
The final criterion in the UFC is Octagon control, referring to which fighter better uses the space, particular the centre, of the Octagon, as well as the pace of the fight, but is very rarely used as a deciding factor in a round.
As per the official Unified Rules of Mixed Martial Arts:
“Legal blows that have immediate or cumulative impact with the potential to contribute towards the end of the match with the IMMEDIATE weighing in more heavily than the cumulative impact. Successful execution of takedowns, submission attempts, reversals and the achievement of advantageous positions that produce immediate or cumulative impact with the potential to contribute to the end of the match, with the IMMEDIATE weighing more heavily than the cumulative impact.”
Judges consider all of the above, generally awarding one fighter a 10-9 round, or occasionally 10-8. 10-10s can be given, but are more rare than 10-9s and 10-8s, and should only be handed out in the extremely rare instances of both fighters being identical in a round, rather than an excuse not to award a round to one fighter the other.
Unanimous decision - When all three judges agree on who won the fight.
Majority decision - Where two judges score the fight for one fighter, and a third judge scores the fight a draw.
Split decision - Where two judges award the fight to one fighter, and the other judge awards the fight to the other.
Technical decision - Where a fight is stopped prematurely (excluding knockouts/submissions) due to a fighter being unable to continue as a result of an accidental foul (such as an eye poke) after more than half of the rounds have been completed, the judges' scorecards will be taken at the point.
Unanimous draw - Where all three judges score the fight a draw.
Majority draw - Where two judges score the fight a draw and one scores the fight to one fighter.
Split draw - Where each fighter is awarded a win by one judge, and the third judge scores the fight a draw.
Technical draw - The same as a technical decision, but when the fight is scored a draw.