Generating human-readable/usable, short but unique IDs

Base 62 is used by tinyurl and bit.ly for the abbreviated URLs. It’s a well-understood method for creating “unique”, human-readable IDs. Of course you will have to store the created IDs and check for duplicates on creation to ensure uniqueness. (See code at bottom of answer)

Base 62 uniqueness metrics

5 chars in base 62 will give you 62^5 unique IDs = 916,132,832 (~1 billion)
At 10k IDs per day you will be ok for 91k+ days

6 chars in base 62 will give you 62^6 unique IDs = 56,800,235,584 (56+ billion)
At 10k IDs per day you will be ok for 5+ million days

Base 36 uniqueness metrics

6 chars will give you 36^6 unique IDs = 2,176,782,336 (2+ billion)

7 chars will give you 36^7 unique IDs = 78,364,164,096 (78+ billion)

Code:

public void TestRandomIdGenerator()
{
    // create five IDs of six, base 62 characters
    for (int i=0; i<5; i++) Console.WriteLine(RandomIdGenerator.GetBase62(6));

    // create five IDs of eight base 36 characters
    for (int i=0; i<5; i++) Console.WriteLine(RandomIdGenerator.GetBase36(8));
}

public static class RandomIdGenerator 
{
    private static char[] _base62chars = 
        "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
        .ToCharArray();

    private static Random _random = new Random();

    public static string GetBase62(int length) 
    {
        var sb = new StringBuilder(length);

        for (int i=0; i<length; i++) 
            sb.Append(_base62chars[_random.Next(62)]);

        return sb.ToString();
    }       

    public static string GetBase36(int length) 
    {
        var sb = new StringBuilder(length);

        for (int i=0; i<length; i++) 
            sb.Append(_base62chars[_random.Next(36)]);

        return sb.ToString();
    }
}

Output:

z5KyMg
wd4SUp
uSzQtH
UPrGAT
UIf2IS

QCF9GNM5
0UV3TFSS
3MG91VKP
7NTRF10T
AJK3AJU7