SVN create patch from committed code?

If you know commit number, then use

svn diff -c N path

Where N is commit number and path is path to your working copy.

Alternative, when using windows + tortoiseSVN :Go to your sourcecode directory, rightclick on the directory (to open the tortoise context-menu) and select "Show Log", select both revisions (ctrl-click) and then right-click and select "Show differences as unified diff" from the context menu. A window will pop up showing the differences, which you can then save as a patch.

Update: Holding Shift, when clicking on "show differences as unified diff" makes a dialog pop up where you can select the diff options (ignore eol changes, ignore whitespace changes, ignore all whitespaces). This is useful if e.g. the line-endings changed between versions (the entire file would otherwise show up as 'changed')

If you know the revision numbers (e.g. 123 and 124) you can use:

svn diff -r123:124 path/to/my_project_folder > ~/my_project_changes_123_124.patch

See also https://stackoverflow.com/a/25283101/1127583

Though already answered simple version is as below,

1, Source Code Location > Tortoize SVN > show log 
2, Select the revision which has your commit
3, Right Click > select > Show changes as unified diff
4, Pop up with differences of all files in that commit come
5, Copy the entire content and create a new file with the extension of .patch

I referred from below link https://groups.google.com/forum/#!topic/tortoisesvn/xV-hemaFdFU