When a game is analyzed, the engine writes an evaluation next to the position: +1.5, −2.0 or M3. It says who is better and by how much. This article explains what those numbers mean for a player. How the engine calculates them is a separate article: how Stockfish evaluates positions.
The sign: who is better
The evaluation is always given from White’s side:
- Plus: White is better.
- Minus: Black is better.
- 0.0: the position is equal.
+1.2 and −1.2 are the same advantage for different sides. If you are playing Black, −2.0 is a good evaluation for you: you are ahead by about two pawns.
On chess.rodeo the evaluation bar beside the board carries no sign. The number stands on the half that belongs to the side that is ahead.
The number: pawns and centipawns
The size of the advantage is measured in pawns. +1.0 means an advantage of about one pawn. There may be no extra pawn on the board: the evaluation also counts positional gains, such as more space or a safer king.
The engine itself counts in centipawns, hundredths of a pawn. An evaluation of 150 centipawns, 150 cp in engine output, appears on screen as +1.5. Hundredths are there to tell apart moves whose evaluations differ only slightly.
Rough thresholds
The boundaries are approximate, but they work as a guide:
| Evaluation | What it means |
|---|---|
| 0.0 to ±0.5 | Roughly equal, the result is open |
| ±0.5 to ±1.5 | A small advantage: one side has the easier game |
| ±1.5 to ±3.0 | A clear advantage that still has to be converted |
| beyond ±3.0 | Usually winning, often an extra piece |
| M with a number | Forced mate |
Below are three positions with different evaluations.
Diagram 1: roughly equal (≈ 0.0)
In the main openings the evaluation stays near zero until somebody goes wrong.
The small plus for White at the start of a game comes from moving first. While the evaluation stays inside ±0.5, nothing has been decided.
Diagram 2: a clear advantage (≈ +1.5)
White has an extra pawn in a knight endgame: four against three on the same side of the board.
At +1.5 the stronger side plays for a win, and one inaccurate move can bring the evaluation back to equal. Positions like this are worth reviewing, because they show whether you can convert an advantage.
Diagram 3: mate in 3 (M3)
When there is a forced mate in the position, the evaluation in pawns disappears and the engine writes how many moves the mate takes. On chess.rodeo that is M3; elsewhere you will also see #3 and +M3. How much extra material a side has no longer matters in such a position.
An evaluation of −M2 means that Black mates in two. The engine ranks any mate evaluation above any evaluation in pawns.
The evaluation assumes best play
The engine answers one question: how the game ends if both sides play the best moves from here on. It does not predict what will happen in your game.
This is why there can be a tactic on the board at +0.3: the engine assumes the opponent will find the defense. If the opponent misses it, the evaluation after that move will be a different one.
Why the evaluation jumps
The best move leaves the evaluation where it was, because the engine has already counted on it. A weaker move shifts the evaluation toward the opponent, and the weaker the move, the bigger the jump. In an equal position it looks roughly like this:
- Inaccuracy: a loss of half a pawn to a pawn.
- Mistake: one pawn to three.
- Blunder: more than three pawns, for example from 0.0 to −4.0.
Labels on chess.rodeo are set by the loss of winning chances, so in a won position the same loss is priced differently: at +8 a lost pawn changes the winning chances very little, and the move gets no bad label. How the evaluation turns into labels and an accuracy percentage is described in accuracy and move labels.
On the evaluation graph weak moves show as steps: the taller the step, the more the move cost.
How to read the evaluation in your own games
In a review, look for the moves after which the evaluation changed the most:
- Find where the evaluation went toward your opponent (your mistake) and where it went toward you (your opponent’s).
- Open that move and compare it with the engine’s best move.
- Find the cause: a piece was left undefended, or you missed a tactic.
The whole routine is laid out in how to analyze your games.
Related
- Understanding Chess Accuracy: how move labels and the accuracy percentage come out of the evaluation.
- How to Analyze Your Chess Games: a game review step by step.
- How Stockfish Evaluates Positions: where the engine gets the number from.
- Free Chess Analysis: see the evaluation in your own games.