ConceptsRanges and boards
Dynamic and static boards
A dynamic board changes a lot on the next card; a static one barely moves. Rail measures which.
What it is
Some boards stay what they are: on K♦7♣2♥ the best hand on the flop is very often the best hand on the river. Others are in motion: on 8♥7♥6♣ a large share of turn cards complete a draw or create a new one.
Rail measures it by looking at every possible next card and counting how many would change the board: a third card of a suit (a flush becomes possible), a card that adds two or more new straight-making holdings, or an overcard to the board, which counts half. Below 25% of next cards the board is static; from 45% it is dynamic; in between, medium. The river has no next card, so it is neither.
Why it matters
On dynamic boards equities run: a hand that is ahead now may be behind on the turn. Strong hands want to bet so draws pay to see the next card, and medium hands are harder to play.
On static boards there is less to protect against. Small bets, thin value and checking back to control the pot all work better, because the turn rarely changes who is ahead.
The dynamism of a board is also what makes some spots expensive to get wrong: the bigger the swings, the more a passive play can cost.
The maths
Volatility equals the number of next cards that change the board, plus half the overcards that change nothing else, divided by the number of unseen cards.
Worked example
Static and dynamic, side by side
On the flop there are 49 unseen cards.
- K♦7♣2♥: only the aces are overcards and no turn card adds a flush or two straight holdings at once — volatility about 4%. Static.
- 8♥7♥6♣: every heart brings a third heart, and many cards add new straights — volatility about 59%. Dynamic.
- Add a 3♠ to K♦7♣2♥ and the turn board's volatility rises to about 21% — still static.
The flop's texture tells you what exists; its dynamism tells you how fast that will change.
Try it
Build a flop and watch volatility: add a second suited card, close the gaps between ranks, then try a turn card.
Common mistakes
- Slowplaying strong hands on dynamic boards, giving free cards to the draws that beat you.
- Betting big for protection on static boards, where there is little to protect against and only better hands call.
- Treating every two-tone board as dynamic: a two-tone K♦7♦2♣ only reaches medium — the flush draw is its one moving part.
Related concepts
- Board texturePaired, suited, connected, high or low: the board's shape decides which hands and draws exist.
- Bet sizing and polarisationSmall, big or overbet: every size has a job, and the job depends on the board and on which hands you bet.
- Continuation bettingThe preflop raiser betting the flop — often right, never automatic.