30,000+12,000 satellites - 951 in orbit = 41,049 / 143 per launch = 287 more launches
Source of that is from wikipedia:
> On 15 October 2019, the United States Federal Communications Commission (FCC) submitted filings to the International Telecommunication Union (ITU) on SpaceX's behalf to arrange spectrum for 30,000 additional Starlink satellites to supplement the 12,000 Starlink satellites already approved by the FCC.[16]