Your indoor doormat pretty much just has to make sense with your space. At the end of the day, it has to be practical. So, make sure it is positioned in a place that takes the most footfall and doesn't have it stretched beyond the width of the door. If you have double doors, it will naturally have to be bigger. If you're working with a small college dorm room, opt for a mini indoor doormat. However, in general, you can't go wrong with a classic 18" x 30", the standard size for a reason!