How big a step down is allowed at an exterior door threshold?

At the required egress door, the floor or landing can be no more than 1½ inches below the top of the threshold (IRC R311.3.1).

At the required egress door, the IRC limits the drop from the top of the threshold down to the landing or floor to a maximum of 1½ inches. Put another way, the threshold can't stand more than 1½ inches above the floor or landing on either side.

There is an exception on the exterior side: the outside landing or floor may sit up to 7¾ inches below the top of the threshold, but only if the door does NOT swing out over that landing (R311.3.1).

For exterior doors other than the required egress door, the landing or floor is allowed to be up to 7¾ inches below the top of the threshold (R311.3.2).