JMB Builders logo

How to Measure for a Replacement Door — Jamb, Rough Opening, Handing

Four measurements and one photo are enough to buy the right door. Here is what to measure, how to tell the handing, and what to send us so we can confirm it before you pay.

How to measure for a replacement door: measure the door slab (width, height, thickness), the jamb width from wall face to wall face, and the rough opening behind the casing if you can reach it. Then read the handing standing on the side the door swings away from you. JMB Builders confirms the size and hand from your photos for free before you buy, then installs the door across the Twin Cities metro, priced per door.

  • We confirm size and handing from photos, free
  • Priced per door, labor only, any store
  • Quote from photos in 1 business day
  • Licensed MN contractor BC809005
Send photos, get a quoteCall or text 763-204-2099
JMB Builders installer checking a door opening on a Minnesota home

Most wrong door orders come from measuring the wrong thing. The number on the box is the slab size, not the rough opening and not the outside of the jamb. A door sold as a certain width is a slab that width, hung in a jamb that is wider, going into a framed opening that is wider still. Measure the wrong one and the door will not fit, or it will fit with a gap that no amount of shimming fixes.

So the order of business is: measure the slab you have, measure the jamb width (the wall thickness), find the rough opening if you can, and read the handing from the correct side. Then photograph all of it with the tape in the picture. That is what we need to tell you what size door you need, and it takes us minutes to confirm.

JMB Builders installs the door you buy, labor only, across the Twin Cities metro. Send the measurements and photos before you shop. We reply within one business day with the size, jamb width and hand to order, and the install quote. Then buy it at Menards, Home Depot, Lowe's, a lumberyard or online.

What you supply

  • Slab width, height and thickness, measured on the door itself, edge to edge
  • Jamb width: the depth of the frame from finished wall face to finished wall face, not counting the casing
  • Rough opening width and height if the casing is off or you can see the framing; otherwise the outside of the old jamb
  • The handing, read from the side the door swings away from you, plus a photo from that side
  • Exterior doors: a photo of the sill and threshold, and the height from the floor inside to the top of the threshold
  • The door you order after we confirm the numbers, plus lockset and hinges if the unit does not include them
  • Paint or stain — painting is quoted as a separate line, or leave it primed and caulked and paint it yourself

What JMB supplies

  • A free read of your measurements and photos: the size, jamb width and hand to order, within one business day
  • The install: old door or jamb out, new unit set plumb, shimmed at hinges and strike, fastened and foamed
  • Exterior doors: sill pan, flashing tape, sealant and exterior trim or brickmould
  • Interior casing in a standard profile, or matched to the rest of the house, primed and caulked
  • Hinge mortising, lock bore and edge planing when you buy a slab instead of a prehung
  • Painting or staining of the new door and casing when you want it done, quoted as its own line
  • Photos of the finished door in your job folder

How it is priced: per door

Quoted in writing from your photos within one business day. What moves the number:

  • Interior vs. exterior: an exterior door adds the sill pan, flashing, foam and exterior trim
  • Prehung unit vs. a slab fitted to the existing jamb
  • A door that is a different size than the old one, which means the opening gets reframed
  • Jamb width that does not match the wall, which means jamb extensions on one side
  • Rot at the sill or bottom of the old jamb, quoted once we see it
  • Casing reused, standard profile, or matched to the house
  • Number of doors in the same visit

Send the tape-in-the-photo pictures before you buy. A door that is the wrong size costs you a restocking trip; a door that is the wrong hand cannot be flipped once it is prehung.

How long it takes

Confirming your measurements: within one business day. Interior prehung install: an hour or two. Exterior prehung: about half a day. A slab fitted to the old jamb: two to three hours.

How your project works

  1. 1

    Measure and photograph

    Slab width, height and thickness; jamb width; rough opening or outside of jamb; handing from the swing-away side. Tape in every photo.

  2. 2

    We confirm the order

    Size, jamb width, hand, and prehung or slab, within one business day, with the install quote. If something does not add up we ask for one more photo rather than guess.

  3. 3

    You buy the door

    Any store, lumberyard or online. Check the label against what we sent before it leaves the store. Buy the lockset and hinges in the same trip.

  4. 4

    We install it

    Old door out, opening checked, new unit set plumb and square, foamed and sealed, cased, hardware on, adjusted until it latches clean.

Situations and options

Measure the slab

Open the door and measure the door itself: width across the face, height top to bottom, and thickness at the edge. Measure width at the top and bottom and height at both edges; write down the biggest. Interior slabs are thinner than exterior slabs, and the thickness has to match the jamb and the hinges you keep.

Measure the jamb width

The jamb width is the wall thickness: from the finished drywall or plaster on one side to the finished face on the other, measured at the jamb, not including the casing. A 2x4 wall and a 2x6 wall take different jamb widths and the store sells both. Get it wrong and the casing on one side sits proud of the wall.

Find the rough opening

The rough opening is the framed hole behind the casing, wider and taller than the jamb. If the casing is already off or you can pull a piece, measure stud to stud and floor to header. If not, measure the outside of the old jamb and tell us; a prehung in the same slab size will fit the same rough opening in most houses.

Read the handing

Stand on the side the door swings away from you: outside for an entry door, in the hallway for a bedroom door. Hinges on your right means right-hand; on your left, left-hand. Exterior doors add inswing or outswing. Send a photo from that side with the door closed and we check it against the store's label.

Check the sill on exterior doors

Measure from the finished floor inside up to the top of the old threshold, and photograph the threshold from outside and the bottom of the jamb on both sides. Soft wood, a rusted threshold or a gap under the sweep changes what you buy. A new prehung exterior door brings its own sill and has to land on solid subfloor.

Photos to send

Door closed from the swing-away side, door open showing the hinge edge, the tape across the slab width, the tape on the jamb edge showing wall thickness, and the bottom of the jamb at the floor. Exterior: the threshold from outside. Five photos and we can tell you what size door you need.

How to Measure for a Replacement Door — Jamb, Rough Opening, Handing: questions, answered

How do I measure a door for a replacement?

Measure the door slab itself: width, height and thickness, edge to edge, with the door open. Then measure the jamb width, which is the wall thickness from finished face to finished face. If you can see the framing, measure the rough opening too. Last, note the handing from the side the door swings away from you. Send those numbers with photos that show the tape, and we confirm the size to order before you buy.

How do I measure a door rough opening?

The rough opening is the framed hole behind the casing. Pull a piece of casing or look where the drywall meets the jamb, then measure stud to stud for width and from the subfloor to the underside of the header for height. If you cannot get to it, measure the outside of the existing jamb and send that instead; a prehung door in the same slab size fits the same rough opening in nearly every house.

How do I tell the handing of a door?

Stand on the side of the door that it swings away from you. For a front door that is outside; for a bedroom door it is in the hallway. If the hinges are on your right, it is a right-hand door. If they are on your left, it is left-hand. Exterior doors also say inswing or outswing. Stores do not all label handing the same way, so send a photo from that side and we check it against the label before you buy.

What size door do I need?

The size on the box is the slab size. Measure your existing slab, width and height, and buy the same size unless the opening is being changed. Most interior and exterior doors come in a few standard widths and one or two standard heights, and the old slab tells you which one you have. If the old door is gone, measure inside the jamb and send a photo; we work back to the slab size for you.

How do I measure door jamb width?

Measure the wall thickness at the door: from the finished drywall or plaster on one side, across the edge of the jamb, to the finished face on the other side. Do not include the casing. Stores sell one jamb width for 2x4 walls and a wider one for 2x6 walls, and some exterior doors come with a jamb that can be ordered to a custom depth. A photo of the tape laid across the jamb edge lets us confirm it.

Can you confirm my door measurements before I buy?

Yes, and there is no charge for it. Send the slab size, the jamb width, the rough opening or outside-of-jamb size, and photos from the swing-away side, the hinge edge, the jamb with the tape on it and the bottom of the jamb. We reply within one business day with the size, jamb width and handing to order, whether to buy prehung or a slab, and the labor quote to install it.

Get a written quote for this job

Three photos and a sentence is enough. You hear back within one business day. Or text the photos to 763-204-2099.

Free quote from your photos in one business day · No obligation · Licensed contractor

Photos (up to 3 — the fastest way to a price)

One wide shot of the room or wall, one close-up of the trim or opening, one of anything you're unsure about.

Related jobs we do

Prehung vs Slab Door: Which to Buy for a Replacement

Standing in the door aisle wondering whether you need the whole frame or just the door? Here is how a carpenter decides, what to measure, and how to read the handing.

Read more

Labor-Only Door Installation — We Install the Door You Bought

You buy the door, we install it right — entry doors, house-to-garage doors, and interior doors hung plumb, sealed tight, and trimmed out by a licensed Minnesota contractor.

Read more

Fit a Slab Door Into an Existing Jamb

The jamb and casing are fine, the door is not. A bare slab from the store fitted to the frame you have — hinge mortises cut to match, lock bored, edges planed until it swings clean.

Read more

Menards Door Installation — Labor Only, You Buy the Door

The door is sitting in the Menards lumberyard, or already in your garage, and you need someone who will hang it square, seal it and make it latch — not a store referral list.

Read more

Reverse a Door Swing — Rehang a Door to Open the Other Way

The bathroom door that blocks the vanity, the bedroom door that swings into the light switch, the door that would work if it just opened the other way. We rehang it.

Read more

Add a Door to an Existing Wall — Cut a New Doorway

A bedroom that needs its own way into the bathroom, a basement office with the only door on the wrong side, a laundry room you walk around the house to reach. We cut the doorway and hang the door.

Read more

Page reviewed September 24, 2026 · JMB Builders LLC, MN license BC809005 · All doors pages

Where we work

Doors near you

Based in Zimmerman, scheduling across the Twin Cities metro. Closest first:

CallTextSend photos, get a quote