Size comparisons can be difficult. You are dealing with distance which isn't easy when the bird is in the sky and there is nothing to gauge the distance from you with. Also different postures and body shapes confuse the matter. Crows have a different posture and body shape than hawks.
Some of you have some really big birds in your area. My Sibley Field Guide gives 49" (4' 1") as the wingspan of a Red-tailed Hawk, 19" length. American Crow 39" wingspan and 17.5" length.