What Your Pieces Are Worth
A rough shopping list
Pieces are not equal, and having a rough sense of their value stops you from making trades that quietly lose the game. The usual scale counts a pawn as one point, a knight or bishop as about three, a rook as five, and the queen as nine. The king has no number because losing it ends everything.
These numbers are a guide, not gospel. They tell you that giving up a rook for a knight is usually a bad idea, and that two minor pieces are often worth more than a single rook. But they cannot capture the whole truth of a position.
When the numbers lie
A knight stuck in the corner with nothing to do can be worth less than a pawn. A bishop raking across an open board can be worth far more than three. Context decides. A piece is valuable in proportion to what it can actually accomplish right now, not what a chart says.
The two bishops working together are a famous example. On an open board they cover squares of both colors and can dominate from a distance, which is why strong players quietly treasure "the bishop pair" even though the point count says nothing special.
The practical takeaway
Before any trade, ask a simple question: after the dust settles, whose remaining pieces are doing more? If the answer is yours, the trade is good even if the point totals look even. Material is a tool for measuring; activity is what actually wins.