Formula One said in a statement that three races saw a weekend attendance of more than 300,000, with Silverstone leading on 351,000, ahead of Mexico (345,694) and the Australian season-opener in Melbourne (324,100).
A weekend in Formula One runs from Friday practice to Sunday's race.
The Liberty Media-owned sport said more than four million (4,164,948) people attended at least one of the races, an increase of 1.75% on 2018 when there were also a record-equalling 21 rounds.
The 2019 growth in attendances was despite Japan's Suzuka circuit having to remain closed on the Saturday due to a typhoon.
The average attendance per race was 202,146.
A total of eight races had weekend crowds of more than 200,000.
Formula One said the Canadian Grand Prix in Montreal reported the biggest year-on-year rise, with an increase of 14.69%.
Canada will have two race drivers next year in Lance Stroll, who drives for Canadian-owned Racing Point, and Williams' Nicholas Latifi.
The data provided by promoters also showed the Sunday only attendance accounted for 1.77 million, a rise of 4% compared to 2018.
Silverstone -- a home race for Mercedes' six times world champion Lewis Hamilton and most of the 10 teams -- topped the race day crowd with 141,000.
Mexico City came second with 138,435, ahead of the US Grand Prix in Austin, Texas, on 128,000, and Singapore with 115,240 spectators.
The Chinese Grand Prix in Shanghai, which marked the 1,000th championship grand prix, reported a 30% race day increase on the previous year.
Formula One said some of the race day figures had been extrapolated from the total weekend numbers.
"We are delighted to see that over four million fans joined us at our 21 races, beating the attendance figures for last year, including a record-breaking Italian Grand Prix weekend attendance with 200,000 spectators," said Formula One managing director Sean Bratches.
Next year will see a record 22 races, with Germany no longer on the calendar but Vietnamese and Dutch races joining and expecting big crowds. - Reuters