The Doubling Cube — Backgammon's Strategic Masterstroke

What Is the Doubling Cube?

The doubling cube is a six-sided die marked with the numbers 2, 4, 8, 16, 32, and 64. It’s not rolled randomly — it’s used to track and raise the stakes of a backgammon game.

Introduced in the 1920s in New York City, the doubling cube transformed backgammon from a simple racing game into a game of deep strategic judgment. Many players consider cube play the most important skill in backgammon.

How the Cube Works

Initial State

At the start of a game, the cube sits in the center showing 64 (which represents 1× stakes). Either player can make the first double.

Offering a Double

Before your roll, you can offer the doubling cube to your opponent, proposing to double the stakes:

1. You say “I double” and place the cube in front of your opponent at the next power of 2
2. Your opponent has two options:
   • Take (Accept): Continue playing at double stakes. They now own the cube and are the only one who can re-double
   • Drop (Decline): Forfeit the game and lose at the current stakes

Re-doubling

After taking a double, only the cube owner can re-double. The sequence goes: 1 → 2 → 4 → 8 → 16 → 32 → 64.

When to Double

The Basic Principle

Double when your winning chances are high enough that:

• If your opponent accepts, you’re playing a game worth more when you’re likely to win
• If your opponent declines, you win the game immediately

The Magic Numbers

The “Too Good to Double” Situation

If you’re so far ahead (85%+) that your opponent will certainly decline, it might be better not to double — playing on gives you a chance at a gammon (2× points) or backgammon (3× points), which is worth more than a simple win at doubled stakes.

When to Accept a Double

The 25% Rule

If you have at least 25% winning chances, you should accept the double. Here’s the math:

• If you drop, you lose 1 point
• If you take and lose (75% of the time), you lose 2 points
• If you take and win (25% of the time), you gain 2 points
• Expected value of taking: (0.25 × 2) + (0.75 × -2) = -1.0 = same as dropping

Since taking gives you a chance to win (and potentially re-double later), even 22-23% winning chances make taking worthwhile.

The Recube Advantage

When you accept a double, you own the cube. This means you can re-double if the game turns around. This “recube leverage” means you should accept doubles slightly more liberally than the pure math suggests.

The Crawford Rule

In match play (playing to a set number of points), a special rule applies:

When one player is exactly 1 point from winning the match, the doubling cube is not available for one game.

Why it exists: Without the Crawford rule, the trailing player would always double immediately (they have nothing to lose). The Crawford rule preserves the advantage of being close to victory.

After the Crawford game, the cube returns to normal. The trailing player will often double immediately in post-Crawford games.

Cube Strategy Tips

1. Don’t be afraid to double — beginners typically under-double
2. Don’t automatically drop large cubes — the math often supports taking
3. Consider gammon chances — if there’s a significant gammon risk, you need more winning chances to take
4. Double early in contact positions — positions can change quickly
5. Hold the cube longer in racing positions — races are more predictable
6. Learn the Crawford rule — it’s critical in match play