How to Measure a Door and Frame for Replacement
, by United Doors and Locks, 4 min reading time
Nominal size, rough opening, jamb depth and handing — the five measurements that let us quote a replacement door and frame without a site visit.
Most replacement orders that go wrong go wrong at the tape measure. A commercial door is not described the way a residential one is, and the number you read off the leaf is not always the number we order by. Here are the measurements we need, what each one means, and where people usually get them wrong.
1. Door leaf size
Measure the door slab itself, not the opening: width first, then height, then thickness. Take the width across the face of the leaf at the top, middle and bottom, and use the largest figure — older doors sag and a warped leaf will read short in the middle.
Commercial doors are described in feet and inches, so a 36" x 84" leaf is called a 3-0 x 7-0. Standard commercial thickness is 1-3/4". If you measure 1-3/8", you are looking at a residential-weight door, and it will not accept commercial hardware prep.
Common commercial widths are 2-6, 2-8, 3-0 and 3-6. Common heights are 6-8, 7-0 and 8-0. If your measurement lands between two standards, say so rather than rounding — the frame may have been shimmed, or the door may already be a custom size.
2. Frame opening and rough opening
There are two different openings and they are not interchangeable.
The frame opening is the clear space inside the installed frame, measured jamb face to jamb face and from the head down to the finished floor. This tells us what door will fit the frame you are keeping.
The rough opening is the hole in the wall before any frame goes in. For a new frame you generally want the rough opening about 2" wider and 1" taller than the nominal door size, though the exact allowance depends on the frame profile and the wall type. If you are replacing the frame as well, give us the rough opening and let us work back from there.
3. Jamb depth
Jamb depth is the throat of the frame — the dimension that wraps the wall, measured from the face of the wall on one side to the face on the other, including drywall, plaster or any finish material.
This is the measurement most often missed, and it is the one that stops an installation dead. Standard depths include 4-3/4" for a 2x4 stud wall with 1/2" board on both sides, and 5-3/4" or 6-3/4" for thicker assemblies. Masonry openings vary widely. Measure it, do not assume it.
4. Handing
Handing determines which way the hinges and the lock are prepped, and a door prepped for the wrong hand cannot be corrected on site. Stand on the outside of the door — the side you push from, or the side the key goes in — and note which edge carries the hinges and which way the leaf swings.
Hinges on the left and swinging away from you is left hand. Hinges on the right and swinging away is right hand. If the door swings toward you, it is a reverse: left hand reverse or right hand reverse. Exterior doors and stair doors are frequently reverse-bevel.
5. Existing hardware and preps
If you are keeping the frame, the new door has to match the preps already cut into it. Photograph and note:
- Hinge locations — how many hinges, their size (4-1/2" and 5" are common), and the distance from the top of the door to the top of the top hinge.
- Lock prep — cylindrical (a round bore, usually 2-1/8") or mortise (a rectangular pocket in the edge). Measure the backset: the distance from the edge of the door to the centre of the bore. Commercial is usually 2-3/4".
- Strike location — the height of the strike in the frame, measured from the floor to its centre.
- Anything else cut into the leaf — closer reinforcement, exit device prep, vision light, louvre, electric hinge raceway.
Fire-rated openings
If the frame or the door carries a fire label, the replacement must carry an equivalent label and the assembly has to stay compliant. Photograph the label — it is usually on the hinge edge of the door or the hinge jamb of the frame — and send it with your measurements. A labelled opening is not a place to improvise.
What to send us
A photo of the opening from both sides, a photo of any fire label, and the five measurements above are usually enough for us to quote a complete door, frame and hardware package. If you have the original door schedule or a floor plan, send that instead and we will do the takeoff.
Email it to estimates@uniteddoorsandlocks.com or call 346-777-3031 and we will walk the opening with you.