Net run rate compares how quickly a team scores with how quickly it concedes, across the whole tournament. The formula is runs scored divided by overs faced, minus runs conceded divided by overs bowled.
A worked example
A team makes 180 in its 20 overs, a rate of 9.00 an over. It then restricts the opposition to 160 in 20 overs, a rate of 8.00. Its net run rate for that match is +1.000.
Two details that trip people up
If a team is bowled out before its overs are used up, it is counted as having faced its full quota, 20 overs in a T20. And overs are written in balls: 18.3 overs means 18 overs and 3 balls, which is 18.5 overs in the calculation.
Over a tournament, runs and overs are added up across all matches first, rather than averaging each game’s figure.