What’s a good error rate?
Last updated 28 October 2026
Your error rate, often called PR, measures how much you give away through mistakes on each real decision, compared with perfect play. Lower is better, and 0 is perfect. Under 12.5 is a solid club player; under 5 is world class.
What it measures
After a game, a strong backgammon engine looks at every decision you made: each move, each double, each take or pass. For each one it works out how much your choice cost compared with the best one. Your error rate is the average cost per decision, scaled so the numbers are easy to read.
- Only real decisions count. Forced moves, and moves where every choice is about as good, are left out, so a game full of easy moves doesn’t flatter you.
- The dice don’t count. It measures your choices, not your luck: you can play very well and lose, or win with an error rate of 30.
- An error rate of 10 means giving away about 1% winning chances on each decision. A game gives you 15 to 20 real decisions, so that adds up.
The levels
Backgammon Room names five levels, the same five as its bots, so you can see who plays like you.
| Error rate | Level | Bots at that level |
|---|---|---|
| Under 5 | Masters | Victor 4, Selin 2, The Cube |
| 5–7.5 | Strong | Nikos 7, Ingrid 6, Kenji 5 |
| 7.5–12.5 | Club | Ahmet 12, Clara 10, Rosa 8 |
| 12.5–22.5 | Casual | Léo 20, Lina 18, Sam 16 |
| 22.5 and up | First steps | Mia 35, Theo 29, Noor 26 |
Someone who knows the rules but has never studied the game usually starts among the Casual or First steps numbers. Getting into Club means most of the big mistakes are gone; Strong and Masters take a lot of study.
What each level plays like
Backgammon Room’s 15 bots were measured the way the app measures you. The other 14 each played 100 to 400 complete games against The Cube, the strongest, and every game was analysed like yours. Here is how often each one found the best move, and how many big mistakes it made in a game.
| Bot | Level | Error rate | Finds the best move | Big mistakes a game |
|---|---|---|---|---|
 Mia | First steps | 35.2 | 28% | 4.8 |
 Theo | First steps | 29.2 | 31% | 4.4 |
 Noor | First steps | 25.5 | 34% | 4.1 |
 Léo | Casual | 19.9 | 43% | 3.1 |
 Lina | Casual | 18.2 | 44% | 3.0 |
 Sam | Casual | 16.1 | 46% | 2.7 |
 Ahmet | Club | 12.3 | 49% | 2.1 |
 Clara | Club | 10.1 | 55% | 1.8 |
 Rosa | Club | 8.0 | 57% | 1.2 |
 Nikos | Strong | 7.2 | 59% | 1.1 |
 Ingrid | Strong | 6.1 | 60% | 0.8 |
 Kenji | Strong | 5.2 | 62% | 0.6 |
 Victor | Masters | 4.4 | 65% | 0.4 |
 Selin | Masters | 2.0 | 73% | 0.1 |
 The Cube | Masters | 0 | 100% | 0 |
- The weaker levels lose through big mistakes: Mia makes about 5 a game, and they make up 85% of what she gives away. Strong players still miss the best move about a third of the time, but their mistakes are mostly small ones.
- Finding the best move half the time is already Club level. The rest is how much the other moves cost.
- The dice still decide many games. Against The Cube, Mia wins about 1 game in 10, Léo about 1 in 3 and Clara about 2 in 5. A single game says little; the error rate over many games says a lot.
The Cube is GNU Backgammon itself, the engine every game is measured against, so its error rate is 0 by definition. When the app can’t reach the server, the same bots play on the iPhone, within about 2 points of these numbers.
Small and big mistakes
The review sorts each costly decision by what it gave away:
- A small mistake gives away about 1 to 4% winning chances.
- A big mistake gives away more than about 4%. One big mistake can cost as much as a handful of small ones, so they’re the first to fix.
Why it jumps from game to game
A game gives you only 15 to 20 real decisions, so a single big mistake can double that game’s error rate. Look at the average instead: the Progress screen draws each game as a dot and your last 10 games as a line, and shows your level only after 5 Real games. Practice games, where you can take moves back, never count.
Moves and cube decisions also get an error rate each. There are far fewer cube decisions, but a wrong take or pass can cost as much as several weak moves.
How it’s worked out
For the curious: every decision’s cost is measured in equity, the points a position is worth on average, with the cube at 1. The error rate is 500 times the total cost, divided by the number of real decisions. It follows the same rules as eXtreme Gammon’s PR (what counts as a forced move, which cube decisions are too obvious to count), so the numbers are roughly comparable with other apps and sites that show a PR. Backgammon Room’s reviews use GNU Backgammon.
Questions
- Is a lower error rate always better?
- Yes. 0 means every decision was the best one. A higher number means more given away.
- Does playing a stronger opponent change my error rate?
- Very little. It measures your own choices against perfect play, whoever sits across the board. Stronger opponents just make you win less often.
- How do I bring mine down?
- Start with your big mistakes, one kind at a time. How to get better at backgammon has the habits that help most.