How to calculate pot odds?

[Jack Bando]

There are four things you must know to calc pot odds.

1)What's in the center
2)What has already been bet by others during the round
3)How much you have to put in
4)The odds of your hand taking the lead

2-4 is easy enough to figure out.
But how do you do #1 in a B&M? On-line you just look at the number where the dealer is located. But how does a B&M player look at a pile of chips and figure out how much is there? Estimate? Counting? Remembering every street?