4 Big Blue CTO Carbon Block Water Filters 4.5" x 20" Whole House Cardridges 4 Big Blue Carbon Block Filters (5 micron) for a Standard Size Big Blue Housing FREE SHIPPING Standard size filters 4.5x 20 Effectively eliminates many impurities from tap water to offer sparkling clean and great tasting water throughout your whole house. All our filters individually wrapped for freshness and protection while in shipment.