Summary:
This article will explain how to adjust the size of custom option input fields on product pages. The default size of these fields is 40 pixels wide which is often times not long enough to see the full input that is being entered.
Solution:
You can change the size of these fields by adding the following code under System / Configuration / General section / Design / HTML Head / Miscellaneous Scripts :
<style>
.product-options dd input.input-text {
width: 300px; }
</style>
TIP:
You can change the width value to whatever size is needed.