From what I have seen on YouTube chess channels, the IMs and GMs can count material within just a couple of seconds (For example, IM John Bartholomew, and Magnus can assess any position in just a second, but I am not asking to learn that :)
How can they count so fast? For me it takes 5-10 seconds to count material. Any tips would be appreciated.
Strong players do not count material. They know when winning or losing a pawn, an exchange... Assessing a position is more than counting material: king safety, piece activity, pawn structure... all have to be assessed.
I don’t know if and how stronger players count. Because I’m not a strong player. And no strong player tells me the secrets. I don’t even know a real strong player personally. But in Maizelis, The Soviet Chess Primer, 2014, 60 ff you may find some handy and concise explanations about the strengths of pieces and how a position affects the strengths.
For a game they do it as @tpr says; they keep a running tab on the difference.
If you are talking about a position taken out of game context, the simplest method would seem to be cancellation of like material, and then a comparison of whatever is left over. Eventually one just sees it all at once, in the same way that one eventually just sees where all the pieces can move.
Edit: By the way, I mean by looking at the board, not by looking at captured men off the board.
I'm not a strong player, however I never need to count explicitly the material.
Whenever i'm trading pawns or pieces, I just keep in mind the status. If it is equal I don't worry anymore; otherwise, I memorize "I'm a pawn down" or "I'm a quality up" and so on.
And if I forgot what was happening, a glance at a chessboard (1 second or so) is enough to see who has more material
Strong players don't have to count material because their games are mostly even. ;)
I still remember the first Swiss tourney I ever went to. Me and a friend went down the line of the top boards and marveled: "None of these guys are ever down anything!" :D
Wow, "a quality up" (somebody's German)...
Actually it is your math skills that needs to improve in order to count material properly. I go for advanced math and English but it does not mean chess has anything to do with math
Just... don't lose track of your material, mate. ;-)
You probably have in mind puzzles...
Not quite demanding, count each type of pieces. Then check values equality such as Rook + 1 = 1x Bishop + 1x Knight = 2x Bishops = 2x Knights, Queen + 1 = 2x Rooks, etc. Pawn structure also may matters over numbers, is it middle or endgame, etc. That all can be spotted in a second or two at most.