C# | List.TrimExcess Method

Last Updated : 11 Jul, 2025

List<T>.TrimExcess Method is used to set the capacity to the actual number of elements in the List<T>, if that number is less than a threshold value. Syntax:

public void TrimExcess ();

Note:

This method can be used to minimize a collection’s memory overhead if no new elements will be added to the collection.
To reset a List<T> to its initial state, call the Clear method before calling TrimExcess method.
Trimming an empty List<T> sets the capacity of the List<T> to the default capacity.
The cost of reallocating and copying a large List<T> can be considerable, however, so the TrimExcess method does nothing if the list is at more than 90 percent of capacity. This avoids incurring a large reallocation cost for a relatively small gain.
This method is an O(n) operation, where n is Count.

Below programs illustrate the use of List<T>.TrimExcess Method: Example 1:

CSharp

// C# code to set the capacity to the
// actual number of elements in the List
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a List of strings
        List<string> mylist = new List<string>();

        // Inserting elements into List
        mylist.Add("1");
        mylist.Add("2");
        mylist.Add("3");
        mylist.Add("4");
        mylist.Add("5");

        // To  display the capacity of list
        Console.WriteLine(mylist.Capacity);

        // To display number of elements in List
        Console.WriteLine(mylist.Count);

        // using TrimExcess method
        mylist.TrimExcess();

        // To  display the capacity of list
        Console.WriteLine(mylist.Capacity);

        // To display number of elements in List
        Console.WriteLine(mylist.Count);
    }
}

Output:

Example 2:

CSharp

// C# code to set the capacity to the
// actual number of elements in the List
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a List of integers
        List<int> mylist = new List<int>();

        // Inserting elements into List
        mylist.Add(45);
        mylist.Add(78);
        mylist.Add(32);
        mylist.Add(231);
        mylist.Add(123);
        mylist.Add(76);
        mylist.Add(726);
        mylist.Add(716);
        mylist.Add(876);

        // To  display the capacity of list
        Console.WriteLine(mylist.Capacity);

        // To display number of elements in List
        Console.WriteLine(mylist.Count);

        // using TrimExcess method
        mylist.TrimExcess();

        // To  display the capacity of list
        Console.WriteLine(mylist.Capacity);

        // To display number of elements in List
        Console.WriteLine(mylist.Count);

        // using clear method
        mylist.Clear();

        // To  display the capacity of list
        Console.WriteLine(mylist.Capacity);

        // To display number of elements in List
        Console.WriteLine(mylist.Count);
    }
}