Answers.Body: <p>According to <a href="http://kirill-kryukov.com/chess/longest-checkmates/" rel="nofollow noreferrer">this site</a>, the worst case for King + Rook vs. King is the following position, requiring 16 moves to mate (White to move):</p>
  
  <pre><code>[FEN "8/8/8/8/8/2k5/1R6/K7 w - - 0 1"]
  </code></pre>
  
  <p>There are other positions which require 16 moves, e.g. with the White King on a1, Rook on e2, and the Black King on d3.</p>
  
  <p>You can play these endgames with an online database viewer, e.g. <a href="http://www.shredderchess.com/online-chess/online-databases/endgame-database.html" rel="nofollow noreferrer">Shredder</a>.</p>
  
  <p>The worst case scenario (for White) with Black to move is when Black is stalemated or can capture the rook, when it is a draw. With White to move, all positions are won.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-22T13:50:06.527Z
Answers.Text: So that means we can deliver checkmate under 16 moves from any position?
Answers.UserDisplayName: berserk
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-22T13:58:01.717Z
Answers.Text: @berserk yes, that's correct.
Answers.UserDisplayName: Glorfindel
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-22T14:36:51.030Z
Answers.Text: except for positions where the rook is immediately captured of course.
Answers.UserDisplayName: user1583209
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-22T17:35:10.460Z
Answers.Text: @user1583209 And positions where the lone king is stalemated (e.g., switch the positions of the two kings in the diagram in this answer).
Answers.UserDisplayName: David Richerby
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-22T23:04:38.190Z
Answers.Text: I'm confused. Is the image depicting the "starting" positions for the 3 pieces, or the "ending" (checkmate) positions? If this is the "checkmate" position, then shouldn't the Rook be Black instead of White (or exchange the two Kings)?
Answers.UserDisplayName: Kevin Fegan
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-23T00:18:32.253Z
Answers.Text: @KevinFegan This is the starting position; from this position it takes 16 moves to mate Black, and there is no position with K+R vs. K where mate is acheivable but it takes longer than 16 moves.  (If the rook were Black it wouldn't be checkmate, because White isn't in check in such a position; instead it's stalemate, as the comment above you notes.)
Answers.UserDisplayName: Steven Stadnicki
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Answers.CreationDate: 2016-11-23T05:32:29.380Z
Answers.Text: @user1583209 yes, except stalemate positions and rook capture positions. I will add this in my question.
Answers.UserDisplayName: berserk
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-23T05:34:57.220Z
Answers.Text: @StevenStadnicki Is there any possible scenario where it takes more than 16 moves to checkmate?
Answers.UserDisplayName: berserk
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-23T06:26:36.817Z
Answers.Text: @berserk There is not (at least not for R+K vs. K) - that's the point of this answer; this is the 'worst-case scenario'.
Answers.UserDisplayName: Steven Stadnicki
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-23T06:37:54.687Z
Answers.Text: @StevenStadnicki oh ok. I got confused with what you said before "but it takes longer than 16 moves".
Answers.UserDisplayName: berserk
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-23T08:40:29.577Z
Answers.Text: @berserk Steven wrote "_there is no position_ with K+R vs. K where mate is achievable but it takes longer than 16 moves" (emphasis mine).
Answers.UserDisplayName: David Richerby
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-23T09:45:42.337Z
Answers.Text: Is the position in the diagram the only position (apart from equivalent positions in the other 3 corners of the board) where it takes 16 moves?
Answers.UserDisplayName: user1583209
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-23T09:59:40.980Z
Answers.Text: @user1583209 no, there are more positions. I updated my answer.
Answers.UserDisplayName: Glorfindel
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Answers.LastActivityDate: 2016-11-23T09:59:27.363Z
Answers.LastEditDate: 2016-11-23T09:59:27.363Z
Answers.UserDisplayName: Glorfindel
Body: <p>Assuming that both players do the best move, I want to know the minimum number of moves needed in the worst case scenario when checkmating a lone king using king and rook.</p>
  
  <p><strong>Edit</strong>: The worst case does not include "stalemate" or "king able to capture rook" positions, as it will be clearly draw in that cases.</p>
  
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-11-22T17:34:48.327Z
Comments.Text: https://en.wikipedia.org/wiki/Checkmate#King_and_rook
Comments.UserDisplayName: David Richerby
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-11-23T05:41:59.267Z
Comments.Text: @DavidRicherby I see, it is written there that it can be forced in 16 moves. You can also post it as answer :)
Comments.UserDisplayName: berserk
Tags: <endgame><checkmate>
Title: What are minimum number of moves needed to checkmate a king using king and rook?
ThreadText: # What are minimum number of moves needed to checkmate a king using king and rook?
  
  (Asked by: username_0 on 2016-11-22)
  
  Assuming that both players do the best move, I want to know the minimum number of moves needed in the worst case scenario when checkmating a lone king using king and rook.
  
  **Edit**: The worst case does not include "stalemate" or "king able to capture rook" positions, as it will be clearly draw in that cases.
  
  **Tags:** endgame, checkmate
  
  > **Comments:**
  > **username_1**: https://en.wikipedia.org/wiki/Checkmate#King_and_rook  
  > **username_0**: @username_1 I see, it is written there that it can be forced in 16 moves. You can also post it as answer :)  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_2 on 2016-11-22. Score: 8 | Accepted answer
  
  According to [this site](http://kirill-kryukov.com/chess/longest-checkmates/), the worst case for King + Rook vs. King is the following position, requiring 16 moves to mate (White to move):
  
  ```
  [FEN "8/8/8/8/8/2k5/1R6/K7 w - - 0 1"]
  
  ```
  
  There are other positions which require 16 moves, e.g. with the White King on a1, Rook on e2, and the Black King on d3.
  
  You can play these endgames with an online database viewer, e.g. [Shredder](http://www.shredderchess.com/online-chess/online-databases/endgame-database.html).
  
  The worst case scenario (for White) with Black to move is when Black is stalemated or can capture the rook, when it is a draw. With White to move, all positions are won.
  
  > **Comments:**
  > **username_0**: So that means we can deliver checkmate under 16 moves from any position?  
  > **username_2**: @username_0 yes, that's correct.  
  > **username_3**: except for positions where the rook is immediately captured of course.  
  > **username_1**: @username_3 And positions where the lone king is stalemated (e.g., switch the positions of the two kings in the diagram in this answer).  
  > **username_4**: I'm confused. Is the image depicting the "starting" positions for the 3 pieces, or the "ending" (checkmate) positions? If this is the "checkmate" position, then shouldn't the Rook be Black instead of White (or exchange the two Kings)?  
  > **username_5**: @username_4 This is the starting position; from this position it takes 16 moves to mate Black, and there is no position with K+R vs. K where mate is acheivable but it takes longer than 16 moves.  (If the rook were Black it wouldn't be checkmate, because White isn't in check in such a position; instead it's stalemate, as the comment above you notes.)  
  > **username_0**: @username_3 yes, except stalemate positions and rook capture positions. I will add this in my question.  
  > **username_0**: @username_5 Is there any possible scenario where it takes more than 16 moves to checkmate?  
  > **username_5**: @username_0 There is not (at least not for R+K vs. K) - that's the point of this answer; this is the 'worst-case scenario'.  
  > **username_0**: @username_5 oh ok. I got confused with what you said before "but it takes longer than 16 moves".  
  > **username_1**: @username_0 username_5 wrote "_there is no position_ with K+R vs. K where mate is achievable but it takes longer than 16 moves" (emphasis mine).  
  > **username_3**: Is the position in the diagram the only position (apart from equivalent positions in the other 3 corners of the board) where it takes 16 moves?  
  > **username_2**: @username_3 no, there are more positions. I updated my answer.  
  
  ---
  
  