A gutshot straight draw has four outs; an open-ended straight draw has eight. By the river those are 16.47% and 31.45%, roughly double, and both sit in the same poker odds chart rather than in separate tables.
Why one rank produces four cards
A gutshot is a draw completed by a single rank. Four cards of that rank are still unseen, so the out count is four. The shape matters because the count is fixed by the number of completing ranks, not by which cards a player holds or by where the gap sits inside the sequence. One rank always means the same four cards.
The table gives 8.51% for the next card and 16.47% by the river for those four outs. Use 8.51% when one card is coming and 16.47% when two are. They answer different questions, and a pot-odds comparison built on the wrong one will be off by a wide margin.
Why two ranks produce eight cards
An open-ended draw has two ranks that complete the straight, one at each end. Each rank supplies four unseen cards, which is why the count is eight rather than four. That is the entire difference between the two shapes: twice as many completing ranks, twice as many outs, and no other variable in the count.
For eight outs the table reads 17.02% on the next card and 31.45% by the river. On a single card, four outs at 8.51% and eight outs at 17.02% sit in a clean relationship. Read that pair together when the question concerns one street; a doubled out count behaves like a doubled single-card chance there, and the row to carry into a one-card calculation is the Next Card row.
Where the river changes the ratio
Across two streets that relationship stops being clean. Four outs give 16.47% by the river and eight outs give 31.45%. The second figure is not twice the first, because the two cards are dealt in sequence from a shrinking deck. The exact calculation counts the ways to miss on both streets and subtracts them from the whole, and that subtraction is not linear in the out count.
Those are the two numbers to carry into a two-street comparison: 16.47% for a gutshot, 31.45% for an open-ended draw. Treating the open-ended draw as exactly twice as likely is close enough for a quick read, but it is not the value the table reports. Where the difference matters, the By the River column is the row to use.
Reading the two rows together
| Draw Shape | Outs | Next Card | By the River |
|---|---|---|---|
| Gutshot, one rank completes | 4 | 8.51% | 16.47% |
| Open-ended, two ranks complete | 8 | 17.02% | 31.45% |
The table puts both draw shapes on one grid, with the Next Card and By the River columns side by side. Use the gutshot row for a four-out draw and the open-ended row for an eight-out draw, then take the column that matches how many cards remain. A draw does not change shape between streets, so the row stays put while only the column changes.
That is the practical reason the two shapes are worth naming separately. The out count is fixed at four or eight from the flop onward, and every figure that follows is a function of that count and the number of cards still to come. A player who has identified the shape has already fixed the row; the remaining choice is only the column.