Most contractors use the "butt to butt" method to determine the swing of a
door. This will give you the correct swing. The only time a problem arises is with outswing
doors as they are actually Left Hand Reverse (LHR) or Right Hand Reverse (RHR).
Doors are always handed from the outside of the door so a good way to tell if you have a
reverse hand door is if you are standing facing the outside of the door and you have to backup
(reverse) when opening it, it is a reverse hand door. If the hinges are
on the left side of the door, it is a LHR. If they are on the right side of the door, it is a
RHR.
The outside of an exterior door is obvious. The outside of interior doors is the key side of
the door. Since some interior doors will have a passage or privacy lock
which has no key, a good way to determine the key side is to visualize if you were to put a
keyed lock on that door, which side would you have the key on. This will be the outside of the
door.
So, if you are standing on the outside of the door looking at it and:
The door swings in and to the right, it is a RH.
The door swings in and to the left, it is a LH.
The door swings out and to the right, it is a RHR.
The door swings out and to the left, it is a LHR.
You are probally wondering if any of this really matters. Consider this: using the butt to butt method, you determined a door was a RH. You called in an
order for a 3068 RH door with a 12 x 12 vision lite installed. On a RH door, the screws for the lite kit would be on the pullside (inside) of the door so
that nobody could take the lite kit out from the outside and get in the door. If that door was actually a LHR, the screws would be on the outside of the
door and the lite kit would have to be taken out and reinstalled.
Also, the next time you install an exit device, take a look at the label on the end of the box. Exit devices are only handed as LHR or RHR. If your
supplier didn't put door numbers on your hardware, you would have to pull each device out of the box to see which door it would work on.
You probally won't go wrong using the butt to butt method but if you use the regular and reverse hand method, you are covering all bases.