It does look a lot like a barn owl feather - the general shape, color, speckling, and I think I can see the fuzzy edges characteristic of owl feathers. But I hesitated to comment because it doesn't show the slightest hint of barring. Barn owls are fairly variable in color, but you'd expect
some barring on the primaries, secondaries, and tail. Their smaller feathers (e.g. coverts) show no barring, but by my estimate, based on plantain and crabgrass, the OP's measurements can't be that dramatically wrong. I'd say the feather in the photo is at least ten inches long.
Check the rightmost feather here:
I'm not happy with all the details (shape, shading, pattern of speckling are all slightly different) but it's a better match than anything else I can find.