Most product filters answer "what do you sell?" Very few answer "will this fit?" I work on the Shopify store for Ramaya, a home decor brand. One of the collections is table runner and placemat sets : one runner plus six matching placemats. Customer questions on that page were almost never about colour or fabric. They were about size. "Will a 72 inch runner fit my table?" "Will the runner cover the placemats?" So I built a small calculator that sits on the collection page and answers those...