In Rip Van Winkle, how long is he gone?

Rip disappears for twenty years.

"Ah, poor man, Rip Van Winkle was his name, but it's twenty years since he went away from home with his gun, and never has been heard of since,—his dog came home without him; but whether he shot himself, or was carried away by the Indians, nobody can tell. I was then but a little girl."