| Quick Answer: How Do You Measure a Door? Measure the door slab itself (width x height x thickness), then measure the rough opening (the framed hole in the wall), and finally measure the door frame. For a standard interior replacement, take width at three points and height at two points, use the smallest reading, and add 2 inches to each dimension to find your minimum rough opening. Named door sizes are nominal, a "32-inch door" actually measures about 31-3/4 inches wide. |
By Jeremy Barker, Founder and CEO, Murphy Door®
Published 2026-10-09
Here's the thing: most door measurement mistakes happen in the first 30 seconds. Someone grabs a tape measure, gets one width reading at eye level, and orders a door. The door shows up, the installer discovers the opening is out of square, and what should have been a morning job turns into a two-week headache. We've been building since 2012 and have shipped to 200,000+ households, the measurement call is the most common reason an order gets flagged before it even leaves our Ogden, Utah facility.
This guide covers standard door measurement for replacement interior and exterior doors, pre-hung doors, and the specifics that matter when you're ordering a hidden bookcase door or flush-mount concealed passage. The process is the same at a high level. The tolerance is what changes, and for hidden doors, the tolerance is tight.
Three tools. That's all you need: a tape measure, a level, and something to write with. Go through this section by section and you'll leave with the right numbers the first time.
How to Measure a Door to Replace?
Start with the existing door slab if it's still hanging. This gives you the nominal size. Measure width across the middle of the door (not the frame), height from top to bottom along the hinge side, and thickness. Standard interior slabs run 1-3/8 inches; exterior doors are typically 1-3/4 inches. Write those three numbers down before you touch anything else.
How to Measure an Existing Door for Replacement?
With the door open, measure width from the hinge-side edge to the latch-side edge. Do this at the top, middle, and bottom. Use the smallest number. Measure height on the hinge side from the bottom of the slab to the top. That gives you your slab size. If the slab is already gone, measure the rough opening (the framed hole) and subtract 2 inches from width and 2 inches from height to find the door slab size you need.
Is a 32 Inch Door Exactly 32 Inches?
No. A "32-inch door" is a nominal size. The actual slab width is 31-3/4 inches. Manufacturers subtract 1/4 inch from the nominal width to build in clearance. You'll see this across every standard door size, the named size and the real size are never identical. Order by the nominal size; the manufacturer handles the actual dimension.
Will a 30 Inch Door Fit in a 32 Inch Opening?
Technically yes, with shimming, but you shouldn't plan it that way. A 30-inch slab (actual width 29-3/4 inches) in a 32-inch rough opening leaves about 2-1/4 inches of gap on each side after framing. That's too much to shim cleanly and will require custom casing work. If your rough opening is 32 inches, order a 32-inch door. If you're committed to a 30-inch slab for some reason, plan for a reframe.
Is a 30 Inch Door Actually 30 Inches?
No. The actual slab width is 29-3/4 inches. Same nominal-to-actual gap as every other size. The 1/4-inch reduction is consistent across the industry.
A Murphy Door® hidden door unassembled flush-mount bookcase door shown open in a home office setting. Notice how the door swings clear of the opening, that swing clearance only works if the rough opening was measured correctly before the door was ordered.
What Does a 32 Inch Door Actually Measure?
The slab is 31-3/4 inches wide and typically 80 inches tall (6 feet 8 inches). The pre-hung unit, slab, jambs, and door stop assembled, runs about 33-1/2 inches wide to fit a rough opening of 34 inches. Here's the full breakdown for a standard 32-inch pre-hung interior door:
- Slab width: 31-3/4 inches
- Pre-hung unit width: about 33-1/2 inches
- Required rough opening width: 34 inches (2 inches wider than the unit for shimming)
- Slab height: 80 inches
- Required rough opening height: 82 inches
Is a 32 Inch Door Actually 32 Inches?
The slab is 31-3/4 inches. The unit is wider. The rough opening is wider still. Think of "32 inch" as a catalog name, not a tape-measure number. When a contractor asks for the door size, they want the nominal. When they're framing the rough opening, they work from rough-opening dimensions.
Is a 32 Inch Front Door Too Small?
For most primary entry doors, yes. Local building codes typically require a minimum clear width that a 32-inch slab won't hit once the door stop and jamb are in place. A 36-inch door is the standard recommendation for front entries, the minimum many contractors will install on a main entrance. Check your local building codes for the specific requirement in your jurisdiction.
Is a 36 Inch Door Actually 36 Inches Wide?
The slab is 35-3/4 inches wide. Same 1/4-inch nominal-to-actual gap as every other size. The pre-hung unit will run about 37-1/2 inches wide, and you need a rough opening of about 38 inches to install it with proper shimming room.
Is a 36-Inch Door Actually 36 Inches?
No, 35-3/4 inches for the slab. If you're sizing a rough opening for a 36-inch door, the framed hole needs to be 38 inches wide and 82-1/2 inches tall for a standard 6-foot-8-inch pre-hung unit.
Do You Have to Order a 36 by 83 Inch Door?
Not necessarily. The 83-inch figure refers to the door unit height (frame included), not the slab. Slab height is typically 80 inches (6 feet 8 inches) for standard residential doors. 8-foot slabs at 96 inches exist for taller openings. Order the slab size that matches your existing slab, or order the unit size that matches your rough opening. Measure both before you decide.
Is a 32 Inch Door Actually 32 Inches Wide?
31-3/4 inches for the slab. 33-1/2 inches for the pre-hung unit. 34 inches for the rough opening minimum. Three different numbers from the same "32-inch door." Keep them straight and you won't have a bad day on installation.
What Are the Actual Dimensions for a 36 Inch Entry Door?
| Measurement Point | Dimension |
|---|---|
| Slab width (actual) | 35-3/4 inches |
| Pre-hung unit width | ~37-1/2 inches |
| Rough opening width (minimum) | 38 inches |
| Slab height (standard) | 80 inches |
| Rough opening height (minimum) | 82–82-1/2 inches |
| Slab thickness (exterior) | 1-3/4 inches |
Is a 30 Inch Door Really 30 Inches?
No. 29-3/4 inches for the slab. The pre-hung unit runs about 31-1/2 inches wide, and the rough opening should be 32 inches. A 30-inch door is the minimum comfortable passage width for most interior applications, common in bathrooms and smaller bedrooms.
What Is the Actual Size of a 30 Inch Door?
Slab: 29-3/4 inches wide by 80 inches tall (standard height). Pre-hung unit: about 31-1/2 inches wide. Rough opening: 32 inches wide by 82 inches tall. Thickness: 1-3/8 inches for interior, 1-3/4 inches for exterior (30-inch exterior doors are less common).
Is a 30 Inch Door Too Narrow?
For a wheelchair or mobility-device user, yes. ADA guidelines call for a minimum 32-inch clear width, which a 30-inch slab won't deliver once the door stop eats into the opening. For a standard interior passage in a guest bath or closet, 30 inches works fine. For a primary accessible route, go to 32 or 36 inches and check your local building codes.
How Do You Measure a Door Frame?
The door frame (the jamb assembly) sits inside the rough opening. To measure it, run your tape across the inside face of the jamb from one side to the other, that's your clear opening width. Then measure from the finished floor to the underside of the door stop at the top, that's your clear opening height. These numbers tell you what size slab will actually pass through the frame without binding.
For a frame you're replacing: measure the rough opening width at the top, middle, and bottom. Measure the rough opening height on both sides. Use the smallest number in each direction. The frame you order should be sized so the pre-hung unit fits with 1/4 to 1/2 inch of shim space on each side.
Jamb depth is the third measurement people forget. Measure wall thickness from finished surface to finished surface, that's your jamb depth. Standard interior jamb depth is 4-9/16 inches for a 2x4 framed wall with 1/2-inch drywall on each side. A 2x6 framed wall needs a 6-9/16-inch jamb depth. Order the wrong depth and your casing won't sit flat.
How Does Measuring Change for a Hidden Bookcase Door?
Here's where I'll be direct, because this is what we deal with every week at Murphy Door®. A hidden door has tighter tolerances than a standard door in one critical area: the reveal. We build to a 3/16-inch reveal on all four sides. Bigger than that and the wall effect breaks down, you can see it's a door. Smaller and it binds in summer humidity.
We figured out the reveal spec the hard way around year three. Once we locked it in, we started shipping shim stock pre-cut for that exact gap with every door. Your contractor gets a tested door, shim stock sized for the reveal, and a written torque spec for the hinge bolts. They can hang it in a morning if, and this is the variable, the rough opening is square.
Here's how to measure for a Murphy Door® hidden bookcase door:
- Rough opening width: measure at top, middle, and bottom. Use the smallest number.
- Rough opening height: measure on hinge side and latch side. Use the smallest number.
- Check for square: measure both diagonals corner to corner. If they differ by more than 1/4 inch, the opening is out of square. We ship a frame kit to correct this, you don't need to reframe, but you do need to account for it.
- Wall thickness (jamb depth): standard is 4-9/16 inches. Measure yours; older homes vary.
- Swing clearance: hidden doors swing into a room. Confirm there's at least the door width plus a few inches of clear floor space in the swing arc.
Our measurement charts page has printable guides you can hand directly to your contractor. Use them. The number of installs that go sideways because someone eyeballed the rough opening is higher than you'd think.
The Hidden Bookcase Door starts at $1,440.00. The Unassembled Murphy Door® Bookcase (our DIY option, starting at $1,000.00) ships with the same measurement requirements, you build the face, we supply the pre-engineered carcass and hardware. Either way, the rough opening measurement is what drives everything.
The Hidden Flush Mount Walnut Wine Rack Door, a good example of how tight the reveal tolerance has to be for the wall effect to work. When that gap is right, nothing about this unit reads as a door. Off by even 1/4 inch, the illusion breaks. That's why we measure rough openings at three points, not one.
How to Measure for a Pre-Hung Door?
A pre-hung door comes as a complete unit: slab, hinges, jambs, and door stop assembled together. To order the right size, you need the rough opening dimensions, not the old slab size, and not the old frame size.
Measure the rough opening width at top, middle, and bottom. Measure height on both sides. Use the smallest number in each direction. Subtract 2 inches from the width and 2 inches from the height. That's the nominal door size to order.
Picture this: rough opening measures 36 inches wide (smallest of three readings) by 82 inches tall (smallest of two readings). Subtract 2 from each. Order a 34-inch pre-hung door at 80 inches. The 2 inches of difference, 1 inch per side on width, split between top and bottom on height, gives the installer room to shim the unit plumb and level.
If you're ordering a Pantry Murphy Door® (starting at $2,800.00) or any of our flush-mount hidden doors, the same rough-opening logic applies. We size the door unit to the nominal door size you order. The rough opening needs to be that nominal size plus 2 inches in each direction. Our team at 888-458-5911 can walk through your specific opening dimensions before you order if you want a second set of eyes on the numbers.
For French door configurations, the math changes slightly, you're splitting the width across two panels. Browse our hidden French door collection and note that each listing specifies the rough opening requirement for the full double-door unit. The Wine Rack French Door starts at $3,640.00 and the Mirror Closet French Door starts at $5,700.00, both require rough openings measured the same way as any double-door unit.
What Common Measurement Mistakes Should You Avoid?
Look, here's what we've learned after serving 200,000+ households. The same mistakes show up over and over:
- Measuring the slab instead of the rough opening. The slab tells you what's there. The rough opening tells you what you can put there. For replacement work, you need both.
- One measurement per dimension. Always take width at three heights and height at two sides. Openings aren't perfectly parallel. Use the smallest reading.
- Forgetting jamb depth. Order a door unit with a 4-9/16-inch jamb for a 6-9/16-inch wall and you'll have a 2-inch problem on both faces.
- Assuming square. Measure both diagonals. Out-of-square openings are common in homes more than 20 years old. A door unit dropped into an out-of-square opening will bind, gap, or both.
- Ignoring swing clearance. Especially critical for hidden doors. The door swings into a room. That arc needs to be clear of furniture, trim, and traffic paths.
We've been at this long enough to know which corners to cut and which corners to weld. Measurement is not a corner to cut. Get the numbers right once, and the rest of the process is straightforward.
If you want to go deeper on how hidden doors are engineered, our page on what actually makes a hidden bookcase door work covers the hinge system, pivot point, and construction details. Every Murphy Door® hidden door is built on Vaultwood Core (a proprietary MDF engineered stronger than standard MDF) with real wood veneer, solid hardwood face frames, and solid-wood components, backed by a Lifetime Warranty on Hardware, Wood, and Workmanship. The Patented Ball Bearing Lower Pivot Point is part of a hinge and hardware system tested to 1,540 lbs, and our bookcase doors handle 400 lbs of shelf load on doors up to 36 inches wide. None of that engineering matters if the rough opening measurement is wrong from the start.
Murphy Door® unassembled flush-mount bookcase French doors shown in action. The two-panel format requires the rough opening to be measured as a single unit, then divided, getting that center point wrong by even 1/2 inch throws both panels out of alignment. This is why we include a full measurement checklist with every DIY kit order.Start Your Project
Questions about your specific rough opening, wall thickness, or swing clearance? Call us at 888-458-5911. Our team in Ogden, Utah builds nearly 100 doors per day and has seen every opening configuration you can imagine. We'd rather spend 10 minutes on the phone with you before you order than troubleshoot a sizing issue after the door ships. You can also visit murphydoor.com/pages/measurement-charts for printable measurement guides, or browse the full door solutions collection to find the right hidden door for your space.
About Murphy Door®
Murphy Door®, headquartered in Ogden, Utah, is the largest hidden door company in the world, having built the category to what it is today. We've been hand-building hidden doors since 2012 and have shipped to over 200,000+ households from our Utah and Kentucky factories. Every Murphy Door® hidden door is built on Vaultwood Core (a proprietary MDF engineered stronger than standard MDF) with real wood veneer, solid hardwood face frames, and solid-wood components. The Patented Ball Bearing Lower Pivot Point is part of a hinge and hardware system tested to 1,540 lbs. Every door ships pre-hung, fully assembled, and QA-inspected before it leaves our factory. We back every door with a Lifetime Warranty on Hardware, Wood, and Workmanship. Murphy Door® is a registered trademark. Call 888-458-5911 or visit murphydoor.com.
Frequently Asked Questions
Q: How do you measure a door frame for an interior door?
A: Measure the inside face of the jamb from one side to the other at three heights, top, middle, and bottom. Use the smallest reading. Measure height from finished floor to the underside of the door stop at two points (both sides of the frame). Also measure jamb depth (wall thickness from finished surface to finished surface), standard 2x4 walls with 1/2-inch drywall on each side run 4-9/16 inches. You need all three dimensions to order the right pre-hung unit.
Q: How do you measure a door opening for replacement?
A: Measure the rough opening (the framed hole, not the frame itself) at three widths and two heights. Use the smallest number in each direction. Subtract 2 inches from width and 2 inches from height to find the nominal door size to order. For a hidden door specifically, also check for square by measuring both diagonals, if they differ by more than 1/4 inch, the opening needs a frame kit before the door unit goes in.
Q: How do you measure for a pre-hung door?
A: Measure the rough opening width at top, middle, and bottom; use the smallest. Measure height on both sides; use the smallest. Subtract 2 inches from each dimension. That gives you the nominal door size to order. The 2-inch difference (1 inch per side on width) gives the installer shim room to set the unit plumb and level. If your rough opening is 34 inches wide by 82 inches tall, order a 32-inch pre-hung door at 80 inches.
Q: How to measure interior door size for replacement?
A: If the old door is still hanging, measure the slab: width at the middle, height on the hinge side, and thickness. That gives you the replacement slab size. If the slab is gone, measure the rough opening and subtract 2 inches from width and 2 inches from height. Don't measure the frame opening and assume that's the slab size, the jambs and door stop eat into the frame dimension and will give you a number that's too small.
Q: Is a 32 inch door actually 32 inches wide?
A: No. The slab is 31-3/4 inches wide. "32 inch" is the nominal size used in catalogs and by contractors. The pre-hung unit is about 33-1/2 inches wide. The rough opening needs to be 34 inches wide to accommodate the unit with shim room. This nominal-to-actual difference (1/4 inch less than the named size) is consistent across the industry for all standard door sizes.
Q: How to measure a door frame for replacement without removing the old frame?
A: You can estimate the rough opening by measuring the old frame's inside width and adding about 2 inches for the jambs on each side (4 inches total added to interior width). For height, add about 1-1/2 inches to the interior frame height. These are estimates, actual rough opening may vary. If you can pull the casing trim and expose the edge of the jamb against the framing, you'll get a true rough opening measurement. For hidden doors, we recommend exposing the rough opening to confirm before ordering.