Counting Characters Entered

This involves the use of an order form used to process a purchase via Paypal. The items are small rhinestone letters for names and such.

The form is very simple in that the purchaser enters into form field one: the letters they wish to purchase.
Form field two (this is where I rely on common sense by the purchaser): enter the number of letters entered in form field one.

Based on the number of letters entered in form field two, my form processes the correct cost for the purchase.

As you have already figured out, I am beginning to see people enter their letter orders w/out entering the number of letters ordered.

All that said: a way to count the letters entered in form field one and auto-populate form field two with that number. Code: