String.Format converts the value of objects into strings based on the given formats. Below examples shows how to format double or decimal values to string in C#.

To format the numbers to fixed decimal places, you can use the "0" custom specifier as shown in the below example:

string.Format("{0:0.00}", 1234.568)    // 1234.57
string.Format("{0:0.00}", 1234.562)    // 1234.56            
string.Format("{0:0.00}", 1234.5)      // 1234.50
string.Format("{0:0.00}", 1234.0)      // 1234.00       

To format the numbers to a maximum of two decimal places, you can use the "#" custom specifier as shown in the below example:

string.Format("{0:0.##}", 1234.568)    // 1234.57
string.Format("{0:0.##}", 1234.562)    // 1234.56            
string.Format("{0:0.##}", 1234.5)      // 1234.5
string.Format("{0:0.##}", 1234.0)      // 1234

To format the numbers to any minimum number of digits, you can use the "." custom specifier as shown in the below example:

string.Format("{0:0.0}", 1234.568)    // 1234.6                      
string.Format("{0:0.0}", 1234.5)      // 1234.5
string.Format("{0:0.0}", 1234.0)      // 1234.0

To format the numbers with thousands separator, you can use the "," custom specifier as shown in the below example:

string.Format("{0:0,0.000}", 12345678.901)    // 1,23,45,678.901          
string.Format("{0:0,0.00}", 12345678.901)     // 1,23,45,678.90     
string.Format("{0:0,0}", 12345678.901)        // 1,23,45,679 

To  format positive, negative numbers and zero, you can use ";" custom specifier to split the pattern into 3 sections as shown in the below example:

string.Format("{0:0.00}", 123456.789)    // 123456.79
string.Format("{0:0.00}", -123456.789)   // -123456.79

// {0:[positive];[negative];[zero]}
string.Format("{0:0.00;'negative: '-0.00;zero}", 123456.789)      // 123456.79
string.Format("{0:0.00;'negative: '-0.00;zero}", -123456.789)     // negative: -123456.79
string.Format("{0:0.00;'negative: '-0.00;zero}", 0.0)             // Zero

To align numbers with spaces then use "," before the colon and align numbers to the left use a negative number of spaces.

// Postitive values
string.Format("{0,10:0.0}", 123456.789)       //"    123456.8"
string.Format("{0,10:0.0}", -123456.789)      //"   -123456.8"
// Negative values
string.Format("{0,-10:0.0}", 123456.789)      //"123456.8    "
string.Format("{0,-10:0.0}", -123456.789)     //"-123456.8    "