Length Option

Hi all,



I am just wondering if I can use a textbox option for length of cable?



For instance the length option would just multiply the cost of the cable by however much the cable cost.



A Cable costs £5 per metre and in length a customer would enter “20”, this would mean that the total cost would be £100?



This would be really handy for us as it would mean we would not need to make a drop down list with custom lengths and then the difference in price between them.



Thanks all