Usage rate, aka NBA usage percentage, is an estimate of the percentage of team plays used by a player while he was on the floor. Usage rate can be calculated with how a possession ends: “field-goal or free-throw attempt, or a turnover.
Usage Rate Calculation Formula
100*((Player’s Field Goal Attempts)+0.44*(Player’s Free Throw Attempts)+(Player’s Turnovers))*(Team’s Total Minutes)
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((Team’s Total Field Goal Attempts)+0.44*(Team’s Total Free Throw Attempts)+Team’s Total Turnovers))*5*(Player’s Minutes)

As you can identify on the chart, when a player is on the court, his usage rate indicates that he’s the primary option for his team. His possession is potentially ending with field goal/free throw attempts, or a turnover. But an offensive rebound give an oppurtunuty for another chance in the same possession. Head over to player stats tables to sort or filter players by usage rate values.
Is a higher NBA usage rate always a good thing?
A team must optimize its offensive output by balancing usage rates and the varying offensive ratings of the five players on the court.
The NBA stats show that, for all players, as the player uses more possessions, his efficiency decreases. One player who gets hot in the game can shoulder a larger proportion of a team’s possessions with only a relatively small drop in team efficiency. But the opposite is also true: Players perform more efficiently when they use fewer of their team’s possessions.
Superstars with higher usage rates help supporting players maintain low usage rates, and this allows them to operate closer to their peak team efficiency.