How can I String.Format a TimeSpan object with a custom format in .NET?

For .NET 3.5 and lower you could use:

string.Format ("{0:00}:{1:00}:{2:00}", 
               (int)myTimeSpan.TotalHours, 
                    myTimeSpan.Minutes, 
                    myTimeSpan.Seconds);

Code taken from a Jon Skeet answer on bytes

For .NET 4.0 and above, see DoctaJonez answer.

One way is to create a DateTime object and use it for formatting:

new DateTime(myTimeSpan.Ticks).ToString(myCustomFormat)

// or using String.Format:
String.Format("{0:HHmmss}", new DateTime(myTimeSpan.Ticks))

This is the way I know. I hope someone can suggest a better way.

Personally, I like this approach:

TimeSpan ts = ...;
string.Format("{0:%d}d {0:%h}h {0:%m}m {0:%s}s", ts);

You can make this as custom as you like with no problems:

string.Format("{0:%d}days {0:%h}hours {0:%m}min {0:%s}sec", ts);
string.Format("{0:%d}d {0:%h}h {0:%m}' {0:%s}''", ts);

The Substring method works perfectly when you only want the Hours:Minutes:Seconds. It's simple, clean code and easy to understand.

    var yourTimeSpan = DateTime.Now - DateTime.Now.AddMinutes(-2);

    var formatted = yourTimeSpan.ToString().Substring(0,8);// 00:00:00 

    Console.WriteLine(formatted);

No one has shown approach with decimal format specifier which is my favorite one, especially when used with string interpolation - https://docs.microsoft.com/en-us/dotnet/standard/base-types/standard-numeric-format-strings?redirectedfrom=MSDN#decimal-format-specifier-d

For example:

$"{time.Hours:D2}:{time.Minutes:D2}:{time.Seconds:D2}.{time.Milliseconds:D3}"
// Sample output: 00:00:09.200

You can of course wrap it up in some helper method.