The Spotted Owl is most similar, but can be separated with attention to its barred, not streaked, underpart coloration. Short-eared Owl is similar in size, but is not barred on the chest nor is as heavily streaked below, does not share the concentric rings in the facial disks, has yellow eyes and a dark bill, and is found in quite different habitat. Great Gray Owl is superficially similar, but much larger, gray rather than brown below, and has differently patterned underparts.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.