Print number with commas as 1000 separators in C#

In C#, you can format numbers with commas as thousand separators using various approaches. The most common and efficient methods involve using format strings with the ToString() method or composite formatting.

Syntax

Following is the syntax for formatting numbers with thousand separators −

number.ToString("N")           // Standard numeric format
number.ToString("#,##0.##")   // Custom format with commas
string.Format("{0:N}", number) // Composite formatting

Using Standard Numeric Format ("N")

The "N" format specifier automatically adds thousand separators and formats the number according to the current culture −

using System;

public class Program {
   public static void Main() {
      double number1 = 1234567.89;
      int number2 = 1000000;
      decimal number3 = 9876543.21m;
      
      Console.WriteLine("Using 'N' format:");
      Console.WriteLine(number1.ToString("N"));
      Console.WriteLine(number2.ToString("N"));
      Console.WriteLine(number3.ToString("N"));
   }
}

The output of the above code is −

Using 'N' format:
1,234,567.89
1,000,000.00
9,876,543.21

Using Custom Format Strings

Custom format strings give you more control over the number of decimal places and formatting −

using System;

public class Program {
   public static void Main() {
      double number = 1234567.89;
      
      Console.WriteLine("Custom format examples:");
      Console.WriteLine(number.ToString("#,##0"));        // No decimals
      Console.WriteLine(number.ToString("#,##0.0"));      // 1 decimal
      Console.WriteLine(number.ToString("#,##0.00"));     // 2 decimals
      Console.WriteLine(number.ToString("#,##0.####"));   // Up to 4 decimals
      
      // Handling integers
      int intNumber = 1000000;
      Console.WriteLine(intNumber.ToString("#,##0"));
   }
}

The output of the above code is −

Custom format examples:
1,234,568
1,234,567.9
1,234,567.89
1,234,567.89
1,000,000

Using String Interpolation and Composite Formatting

You can also use string interpolation or string.Format() for inline formatting −

using System;

public class Program {
   public static void Main() {
      double price = 1234567.50;
      int quantity = 50000;
      
      // String interpolation
      Console.WriteLine($"Price: {price:N2}");
      Console.WriteLine($"Quantity: {quantity:#,##0}");
      
      // Composite formatting
      Console.WriteLine(string.Format("Total: {0:C}", price * quantity));
      Console.WriteLine("Formatted: {0:#,##0.00}", price);
   }
}

The output of the above code is −

Price: 1,234,567.50
Quantity: 50,000
Total: $61,728,375,000.00
Formatted: 1,234,567.50

Comparison of Formatting Methods

Conclusion

C# provides multiple ways to format numbers with thousand separators. The ToString("N") method is the simplest approach, while custom format strings like "#,##0.##" offer precise control over decimal places and formatting appearance.