13" x 13"Chimney Cap: All bolts and extended edges are prepared for you to adjust the bottom size for smaller chimneys; extended edges for fitting bigger chimneys. This humanized design makes the chimney cap a perfect outdoor protection solution, saving your extra expenses. It fits flue sizes from 10.7" x 10.7" to 15.4" x 15.4". Durable Stainless Steel: Constructed of 304 stainless steel, the chimney cover features rain, snow and temperature resistance. With our robust design, you will never have to worry about the frame deforming. Therefore, it can be used outdoors for years to come, no matter how terrible the weather is.