Brawn has long stated his desire to keep Formula One's calendar in check despite the arrival of new venues virtually ever year over the past decade.
For next season there could be three new events, with Russia and New Jersey poised to make their debuts - although doubts remain over the latter - and with Austria to return after an 11-year absence.
With India off the agenda for next season - albeit for one year only as supremo Bernie Ecclestone reshuffles the races for 2015 - there may be 21 grands prix in 2014.
Brawn, however, is fearful of the demands being placed on his race team and said: "Twenty races is pretty challenging for the teams with one crew of people.
"I think you reach a need point that when you go beyond it you have to start looking at rotating people, rotating crews.
"That's gets very difficult, particularly with the engineers because they are very closely linked with their drivers.
"That's not an easy thing, but with some of the technicians and mechanics and so on we can do that.
"But 20 races is pretty intense for everyone. One more is only five per cent more; two is only ten per cent more.
"But it really does start to get difficult to manage, so I think 20 is a sensible limit."