C# – String.Concat vs String.Join

September 24, 2010

I had a quick Google search for a comparison between string.concat and string.join, but I couldn’t find anything.

Say you want to construct the sentence “The quick brown fox jumps over the lazy dog”

This is comprised of 9 words, 8 spaces.

Using string.concat:

Using string.join

With String.concat, we must explicitly add the separator (in our case, space) between each string.

String.join however, allows us to specify the separator as the first parameter.


I wrote a small benchmark test on the two (see bottom of this post for code)

We can see string.join consistently performs better

string concat vs string join

Benchmark Code:

Note – This is available on GitHub – http://github.com/alexjamesbrown/StringConcatVsStringJoin


Update – StringBuilder.Append

In the comments, Dejan Stojanović put together a similar test using StringBuilder.Append – with similar, and sometimes slightly better results!

With stringbuilder.append

See this commit for the update


# Back

  • Andrew O Dennison

    You have switched your captions/timers in your Console.WriteLine. s1 is the concat timer, s2 is the join timer. If you use names like joinTimer and concatTimer this would be obvious

    • Sorry, I totally missed this comment (for 2 years it seems)
      Switching to Disqus and Tim’s comment below has alerted me to it!

      I’ll fix this!

  • Tim Schmelter

    Andrew’s comment is two years old but the code is still incorrect. So actually string.Join is faster.

    • You’re right… I’ve replied above, will fix!

  • Thanks to those who pointed out the issues. I’ve fixed the code and made it available on GitHub!

  • Pingback: Zeichenketten in R (und anderen Programmiersprachen) zusammenfügen | Fenon.de()

  • omar salem

    thank you for the experiment

  • Quite interesting. I’ve never thought that using of join method would be so efficient, so thanks for sharing your experience. 🙂

  • I just saw this test and wanted to add one more methods and that is StringBuilder. I was amazed that StringBuilder.Append worked even faster than String.Join.

    As far as I could see in most of the articles on internet, StringBuilder is described as the slowest one, but in this test it had the best score.

    The following is test code and attached are results screenshot

    var stringbuilderStopWatch = Stopwatch.StartNew();

    for (var i = 0; i < numberOfTimesToRun; i++)

    new StringBuilder().Append(space).Append(the).Append(quick).Append(brown).Append(fox).Append(jumps).Append(over).Append(the).Append(lazy).Append(dog);


    • Alex

      Could you fork the repository – https://github.com/alexjamesbrown/StringConcatVsStringJoin and add it as a pull request? I would be interested to see this…

      • Pull request created. Let me know when you take a look at it. I’m really curious to determine which approach for building string is the fastest one 🙂

        • Alex

          Sorry for taking so long to get back to you!
          Pull request merged, and article updated – very impressive results.

    • caleb_lyle

      I think this isn’t an accurate test. StringBuilder’s Append method works like string.Concat and not string.Join so you have to append the space between each word. Also, just doing the appends will not return a string, but a StringBuilder object. You have to call ToString after to get the string.

      Here is an example:

      new StringBuilder().Append(the).Append(space).Append(quick).Append(space).Append(brown).Append(space).Append(fox).Append(space).Append(jumps).Append(space).Append(over).Append(space).Append(the).Append(space).Append(lazy).Append(space).Append(dog).ToString();

      When I add these changes, it looks like string.join is faster.
      Sorry for replying to an old post


  • Tanner Watson

    FYI – string.Join is backed by StringBuilder.