How do I calculate a MD5 hash from a string?

It is a common practice to store passwords in databases using a hash. MD5 (defined in RFC 1321) is a common hash algorithm, and using it from C# is easy.

Here’s an implementation of a method that converts a string to an MD5 hash, which is a 32-character string of hexadecimal numbers.

public string CalculateMD5Hash(string input)
// step 1, calculate MD5 hash from input
MD5 md5 = System.Security.Cryptography.MD5.Create();
byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes(input);
byte[] hash = md5.ComputeHash(inputBytes);

// step 2, convert byte array to hex string
StringBuilder sb = new StringBuilder();
for (int i = 0; i < hash.Length; i++)
return sb.ToString();

An example call:

string hash = CalculateMD5Hash(“abcdefghijklmnopqrstuvwxyz”);

…returns a string like this:


To make the hex string use lower-case letters instead of upper-case, replace the single line inside the for loop with this line:


The difference is the ToString method parameter.

[author: Jani Järvinen, C# MVP]