How many queens can be on the chess board at most?

Inagine that we can deliberately design a moving process of pieces, to promote all the pawns of both sides. If all the pawns are promoted to queens,  there will be 18 queens on the chess board. But is this idea possible to come ture? 

If it's impossible,  can we know how many queens can be on the chess board at most?

Funny idea, it's needed to only take quality pawns and make few double pawns columns

64

18 queens is possible

Here's an example game in which 18 queens could theoretically happen with legal moves. However, it would be extremely unlikely to ever happen in a real game. As the pawns start out blocking each other, some pieces need to be sacrificed in order to double all of them (incredibly unlikely), then they need to pass each other without capturing (effectively impossible) and finally all promote without being captured by the enemy king/pieces (also unlikely). As a bit of trivia, this position I think has almost the most total possible material in a chess game (almost because I sacked a rook instead of bishop, making it off by two), being 2 white rooks + 2 black rooks + 1 white queen + 1 black queen + 8 promoted black queens + 8 promoted white queens = 164.

#6
That is a known problem: 8 queens can be on the board without attacking each other.

https://en.wikipedia.org/wiki/Eight_queens_puzzle#:~:text=The%20eight%20queens%20puzzle%20is,row%2C%20column%2C%20or%20diagonal. 

Here's a 7x7 setup to #6

 

Note that the previous positions are when every queen can each any other queen. If you limit it to where queens can only attack queens of the opposite colour, and you allow kings to block their queens, then you can have 9x2 queens not attacking each other, such as in this impossible position (the number could probably be even higher if there are more pieces to block), there should also be a black queen on d7 but due to some glitch in chess.com, for some reason it won't allow me to put a piece there.

It is possible to reach a position with 18 queens. It can be done trillions of ways, presumably.

What if the board was covered in queens…?

[Event "Computer Game"]
[Site "Chess.com iPhone"]
[Date "2023.01.28"]
[Round "?"]
[White "REroepoe37"]
[Black "Beginner"]
[Result "1-0"]
[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
[WhiteElo "171"]
[BlackElo "400"]
[Termination "REroepoe37 wins by Checkmate"]

1.e4 c5 2.Nc3 Nc6 3.Nf3 e6 4.d4 cxd4 5.Ne2 b5 6.Bg5 Nf6 7.Bxf6 Qxf6 8.e5 d5 9.exf6 Bd6 10.Ng5 a6 11.Nxh7 Rxh7 12.g4 Nb8 13.g5 Bxh2 14.g6 Rh5 15.Ng3 Nd7 16.Nxh5 gxf6 17.gxf7+ Kxf7 18.Qxd4 Be5 19.Qd1 Nc5 20.Bxb5 axb5 21.c4 Bd6 22.f4 dxc4 23.f5 Bb7 24.fxe6+ Kxe6 25.Qe2+ Be5 26.Nf4+ Kf5 27.Rh5+ Kxf4 28.Qc2 Ra4 29.b3 Ke3 30.bxa4 Nxa4 31.Kd1 Bc8 32.Qh7 Bxa1 33.Kc1 Kf3 34.Kb1 Bg4 35.Kxa1 b4 36.a3 c3 37.axb4 Bc8 38.b5 Be6 39.b6 Ke2 40.b7 Ke3 41.b8=Q f5 42.Rh3+ Ke2 43.Rh1 Kd2 44.Rh2+ Kd1 45.Rh1+ Kc2 46.Qhh2+ Kd3 47.Qg1 Ke4 48.Qe1+ Kd4 49.Qc1 Ke4 50.Qd1 Bf7 51.Qxa4+ Kd5 52.Qa3 Be8 53.Qxc3 Bg6 54.Qf3+ Kd4 55.Qfg3 Bf7 56.Qf3 Kc5 57.Qxf5+ Kd4 58.Qxf7 Kd3 59.Qbb3+ Ke2 60.Qb1 Ke3 61.Qbb3+ Kd2 62.Rh2+ Ke1 63.Qb1# {1-0}

You can't have 18 queens. It's impossible! There're eight pawns on a chessboard and one queen. If all the pawns turn into a queen and the 1st queen is still on the chessboard, it's 9. 8 queens + 1 queen = 9 queens ( 8 + 1 = 9). So there can be up to 9 queens on a chessboard. So, tygxc 18 queens isn't not possible.

9 white Queens + 9 black queens = 18 queens

Here is a game (unrealistic, but legal) in which the final position has 18 queens and a combined mobility (counting both sides) of 324.

128, 34 or more. You didn't say the size of the board