How to Use LINQ Count in C# - Simple Guide

Use Count() from LINQ in C# to count elements in a collection. You can call Count() without parameters to get the total number of items, or pass a condition as a lambda expression to count only items that match it.

Syntax

The Count() method has two common forms:

• collection.Count(): Counts all elements in the collection.
• collection.Count(condition): Counts elements that satisfy the condition (a lambda expression returning true or false).

This method is part of the System.Linq namespace.

csharp

int total = collection.Count();
int filtered = collection.Count(item => item.Property == value);

Example

This example shows how to count all numbers in a list and how to count only even numbers using LINQ Count().

csharp

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6 };

        int totalCount = numbers.Count();
        int evenCount = numbers.Count(n => n % 2 == 0);

        Console.WriteLine($"Total numbers: {totalCount}");
        Console.WriteLine($"Even numbers: {evenCount}");
    }
}

Output

Total numbers: 6
Even numbers: 3

Common Pitfalls

Common mistakes when using Count() include:

• Forgetting to include using System.Linq; which causes Count() to be unavailable.
• Using Count() on large collections repeatedly inside loops, which can hurt performance because it enumerates the collection each time.
• Confusing Count() with Length or Count property on arrays or lists; Count() is a method from LINQ and works on any IEnumerable.

Wrong:

var count = myList.Count; // works only if myList is List or array
var count = myEnumerable.Count; // error if myEnumerable is IEnumerable without Count property

Right:

using System.Linq;
var count = myEnumerable.Count();

Quick Reference

LINQ Count Cheat Sheet:

Usage	Description
collection.Count()	Count all elements
collection.Count(x => x > 10)	Count elements matching condition
using System.Linq;	Required namespace

Usage	Description
collection.Count()	Count all elements
collection.Count(x => x > 10)	Count elements matching condition
using System.Linq;	Required namespace

Key Takeaways

Always include 'using System.Linq;' to use LINQ Count.

Use Count() without parameters to count all items in a collection.

Use Count(condition) with a lambda to count items that meet a condition.

Avoid calling Count() repeatedly on large collections inside loops for better performance.

Count() works on any IEnumerable, unlike Count property which is only on some collections.