How are you making the measurements? Are you measuring frame side to frame side, or the actual door itself? Pictures help.

 

A 34" door is really only 33 3/4".
Ever done this before? It's a royal pain unless you have all the right tools and know how.

 

I'm measuring just the door.

 

joe is right that is the size of 34" door and changing just the door is a pain. It's much easier to buy a prehung door and change everything at once.

 

I did the same thing you want to do a few years ago. You'll need a router and a hinge template. I found that the new doors were slightly taller than what I was replacing, so I had to cut about 1/4" off the bottom of most of them to clear the carpet.

The job is tedious but not really hard. Just be sure to measure very carefully for the hinges. And, if you don't already know, solid core doors are heavy.

 

34" doors are actually 33 3/4" ??????? that must be a u.s thing or something unless your measuring teh wrong side of the door as per the lean of the door which is usually 1/8 each side. here a 34" door is a 34 " door unless its a bifold then its actually 1/4" narrower

as per replacing the entire door with a new prehung hows that less work. you have to remove the casing, remove the old jamb, hang the new door, case it. hope the baseboard will still butt up to the new casing without being too short or getting damaged when pulling it off the wall.. not to mention most prehung doors are so poorly made now it takes just as much time to mess with the hinges and get the margins right i can hinge a blank door hang it then drill the lockset in less time

 

A door listed as a 34 inch door may not, quite be 34 inches "true".
(Slab size)
Just put a 34 inch door in -
the size of the "slab", was about 33 and 3 quarters.
(Pre-hung door)

 

If you're going to use a solid-core, wood door -
Pull the existing door out -
Put it on top of the new door and mark it - the new door.
Try to cut/plane it to the same, as the old door.
Mark the exact location of the existing hinges -
Make sure the "set-back", from the hinge pins, to the face of the new door is the same as the old door.
Usually, we'll hang the new door, and then drill the lock set.

"RF"

If you're going to use a steel door - find someone who knows how to do it.

 

Here a 34" door would measure 33 3/4"
Put the new blank on a set of saw horses. Lay the old door on top lining up the top and sides.
Then transfer the hinge location, all hardware location to new blank, also mark if you need to cut the bottom, just use the old door as a template, and is not bad at all.
When you do not have the old door as a pattern, it is a pain.

Is also a good idea to carefully examine the old door before removing it. If there is any adjustments to make for the new door. Example, maybe the previous installer cut it to short, now is time to correct it and not cut new door to short also.

 

in the case that theres an old opening with teh hinges already mortised and i dont have the door i make a story pole out of a thin peice of wood that`s the same height of the door plus 1/8". place teh story pole over the jamb butting hard up to the header , then mark teh hinge locations in place. then cut 1/8" off the top of the story pole then mark the hinge locations on the door. the 1/8 allows for the gap between the door and head jamb

 

Thanks - "funfool"!

 

Used to do it all the time after break-ins.
Some 34" doors measure from 33.5 to 34". Yep can be a pain when it is too small.
For one door do it by hand, sharp knife and a sharp chisel.
Story pole is an excellent idea.
Make sure the old door is square and has not been planed to fit.
Cut/plane new door to size. Slight bevel on strike side. If cutting for height cut of bottom.
Mark out and chisel hinges. hang door, drill for knob.

 

i know some guys that like to make the new door fit to the old opening before they open it.. hard to do with only one set of hands. i prefer to get it on the hinges first then try to get it closed then scribe it to the jamb in place. then run the power plane over it till im just at the pencil line then rescribe 1/8 to allow for the margin

 

That works if you have to scribe it and make it smaller but what if you need to be at an angle top or bottom that makes it bigger? I've worked on some old houses where the top and bottom had to be cut on angles.

 

cheat the hinge gains on the door higher on the door so the entire door hits along the header but have the door as close to the opening as possible. a door should always have 1/2" clearance from the floor on the bottom, 3/4" for a closet door so to allow air flow

 

Standard doors today are 32" and 36" wide. 34" wide doors were dropped years ago. Before you cut a 36" door down, be sure that it can be cut. Nothing worse than cutting an inch off of both sides of a door and not having a solid stile left. 34" doors can still be special ordered, but be prepared to pay $$$.