Teams are provided with an allocation of 13 sets of dry weather tyres for the weekend - two hard, three medium and eight soft. They also receive three sets of intermediate tyres and four sets of wets. If FP1 and FP2 are wet and FP3 looks like it will be wet, then the teams may return a set and take an extra set of intermediate tyres.
20 teams, each with 21 sets per weekend and 23 races. So Pirelli supply 9,660 sets or 38,640 tyres for the races. They also need to supply tyres for testing and media days.