Drop down for quantity choice

My store sells yardage.  Minimum sale of 1/2 yard on Regular priced product.  Minimum 1 yard on Sale product.  Most importantly to have a drop down with 1/2 yard increments.  1/2, 1, 1-1/2, 2, 2-1/2 etc... up to 15.  It is like shoe sizes without the width involved.