Friday, July 25, 2008

Are there enough credit card numbers?

I was wondering if the 16 digits that most credit cards have (VISA and Mastercard et al) if you don't include American Express' 13 digit cards were enough for the world or if we'd run out of digits at some point.

If I've done my calculations correctly and based on my assumption that there are 7 billion people in the world then there are enough numbers for each person on earth to have just under 1.5 million credit cards.

I then pulled out my wallet and counted that I have 16 credit card sized items in there (some of which are credit cards) and held together they are about 1cm thick. So my next calculation was to see how fat my wallet would have to be to hold 1.5 million credit cards: 937.5 meters wide, that's almost a Km.

1. I'm not really that tall - I'm just sitting on my credit cards!

2. An interesting thing is the credit cards are coded based on backing company, issuing bank... For example all discover cards start with a 6. Master Card is 5, I beleive.

3. @Paul - you're correct. There's also an algorithm called the Luhn's Algorithm that allows you to quickly calculate if a series of 16 digits could possibly be a credit card. Did you know that if you randomly generated a 16 digit number that it has a 10% change of passing the Luhn Test?