Door handing is something a lot of people struggle with and something we have a lot of calls about because people often order the incorrect handing. Many of the problems seem to lie with the difference in the way carpenters determine handing and how we do. It's not that we're trying to be difficult, the door hardware industry as a whole determines door handing differently than carpenters do - we have to in order to get you the right setup. Customers usually side with their builder, probably because they've already been working with them for months before they finally need door hardware. I think it's great that they trust their builder, but the way door handing is determined for carpentry is a bit different than it is when you order door hardware. So while the carpenter is adamant that he knows how to determine door handing, he may be right [for carpentry] but when ordering door hardware, you should trust the people that do it every day. Why? When a carpenter is hanging doors all he has to worry about is the swing - right or left. When you order door hardware you need to know the swing, but you also have to know which side of the door the lock will be on. This makes things seem a little more complicated but it's actually quite easy if you just follow some simple rules.
Follow These Steps:

step 1 Stand facing the door on the outside - If it's a locking door, stand on the side of the door where you would insert a key (or unlocking tool if it would be a privacy lock). For interior doors you would stand on the side of the door you enter from - i.e. in the hall if a hall closet, in the bedroom if a door opens to a bath, in the kitchen if a door opens to the pantry.
step 2 If the hinges are on the left, it's a left hand door. If the hinges are on the right, it's a right hand door.
 width= To make things a little easier, Schlage and Kwikset have designed their levers to be reversible so you don't have to worry about specifying handing when you order, but most of the other brands you do. It's really pretty simple if you just follow these simple steps above.