Collecting accurate measurements can be the difference between a tricky upgrade and a smooth install. This guide shows how to measure entry door dimensions step by step, with practical tips that prevent returns and rework. Follow each step carefully, take photos as you go, and record measurements that match up accurately with any entry door product page.
Why Perfect Measurement For Your Entry Door Matters
Even a small measuring mistake can cause big problems during installation. Tight tolerances decide if the unit shims square, seals against drafts, and clears finished flooring. Before you start measuring, confirm the type of door you plan to buy. A slab replacement uses the existing frame, so you only measure the panel. A prehung door or door kit comes with a new frame, which means you measure the rough opening instead. Making the right choice upfront ensures a properly sized entry door and a smooth delivery day.
Tools For Accurate Entry Door Measurements
Using the right tools and keeping clear notes will make the process from shopping cart to installation much smoother. Have this kit ready when measuring your entry door.
- Steel tape measure with a rigid standout
- Two or four-foot level to check plumb and level
- Carpenter square for quick corner checks
- Pencil, blue painter tape, and a notepad or phone
- Someone to help hold the tape and take photos
Optional items: laser measurer for long spans, stud finder, small pry bar to peek behind casing
How To Measure A Door Slab Replacement
If your existing frame is solid and square, a slab replacement lets you keep your current trim and paint lines. Follow these steps to record accurate measurements that match the standard ordering fields for an entry door slab.
Height
Close the door and measure the door slab height from top to bottom at three points: left side, center, and right side. Write down the smallest measurement to ensure accuracy.
Width
Measure across the face at the top, center, and bottom. Write down the smallest measurement of the three to ensure accuracy.
Thickness
Measure the edge at the latch side. Most exterior slabs are 1 3/4 inches thick. This measurement ensures the hinges and lock holes will align correctly.
Hinge and lock layout
Note hinge count and leaf size. Record the backset for the latch, usually 2 3/8 or 2 3/4 inches. Take close photos of the hinge side and lock side so prep can be matched during entry door ordering.
Tip: If weatherstripping hides edges, lift the slab onto sawhorses. A stable surface improves accuracy and keeps paint from smearing your tape.
How To Measure A Prehung Or Door Kit Rough Opening
A prehung unit or door kit includes a frame that must fit the wall with room for shims and insulation. Follow these steps to size the opening for a framed entry door.
Width
Carefully remove the interior casing to reveal the wall studs. Measure the width from stud to stud at the top, center, and bottom of the opening. Record the smallest measurement for the most accurate rough opening size.
Height
Measure from the subfloor to the bottom of the header at the left, center, and right. Use the smallest measurement. If finished flooring will be added or removed, note the thickness of the finished floor.
Jamb depth
Measure wall thickness from the interior drywall face to the exterior sheathing or brickmould reference. Common depths are 4 9/16 inches for 2 by 4 walls and 6 9/16 inches for 2 by 6 walls. Matching jamb depth keeps casing flush and avoids shadow gaps on your entry door.
Allowances
Most openings work best when the rough opening is about one-half to three-quarters of an inch larger than the unit in both directions. This space allows shimming and low-expansion foam. Always verify the exact allowance in the specifications of the unit you plan to order.
Sill and threshold
Inspect the sill area to make sure it is flat and level. A solid, level base helps the entry door close quietly and ensures a tighter weather seal after installation.
Other Critical Factors For A Perfect Entry Door Fit
The correct size is only part of the story. These details protect comfort, security, and appearance.
Handing and swing: Stand outside, face the door, and locate the hinges. Hinges on the left define a left-hand door. Hinges on the right define a right-hand door. Decide on an inswing for interior clearance or an outswing for wind exposure and security. Write both on your sheet so your entry door order matches the correct orientation.
Plumb, level, and square: Place a level on both studs and across the sill. Check diagonals corner to corner for racking. Note any lean so you plan shims before the unit arrives.
Glass and hardware prep: Large glass brightens the foyer while changing weight and energy ratings. Confirm handle set, deadbolt, viewer, and smart lock requirements. A precise list avoids late drilling on your entry door.
Delivery path: Measure hall widths, stair landings, and turns. If space is tight, a compact kit that assembles on site moves through corners with fewer scuffs.
Common Measurement Mistakes And How To Avoid Them
These are some of the most common issues when measuring an entry door.
- Taking one reading instead of three and failing to use the smallest
- Measuring to the finished flooring for prehung units instead of the subfloor
- Forgetting the jamb depth so casing ends up proud or shy of the wall
- Ignoring hinge side lean, which leads to latch misses and uneven reveals
- Skipping photos of hinges and backsets that would simplify slab rehangs
- Assuming the old unit size equals the rough opening without removing casing
Quick reference
| Scenario | Record this size | Purpose |
| Slab replacement in a sound frame | Slab height, width, thickness, hinge layout | Order a slab that rehangs cleanly |
| New prehung or door kit | Rough opening width and height, jamb depth | Confirm the frame will fit and shim square |
| Tight halls and stairs | Largest turn width and stair landing sizes | Confirm the unit or kit can reach the opening |
What To Do With Your Measurements
Organizing your notes into a clear packet ensures your order is accurate and avoids costly miscommunication. Use this checklist to finalize your entry door selection:
- Label the door type: slab, prehung, or door kit
- Match sizes to the correct fields: door size for slabs, rough opening, or unit size for framed units
- Add handing and swinging from the exterior side
- Note any planned flooring changes
- Attach photos of the opening, hinge side, sill, and your tape readings
- Share the dimensions with your installer or supplier and ask for a quick review
Choose the Best Material for Your Door to balance durability, security, energy efficiency, and maintenance before you finalize your order.
Make Your Measurements Count
Confirm the type of door you need. For slab replacements, record the height, width, and thickness of the panel. For new frames or prehung doors, measure the rough opening and jamb depth. Always mark the hand and swing from the exterior, and plan the delivery path from the curb to the opening.
With accurate measurements and a clear understanding of key buying terms like 'slab' and 'prehung,' you can select an entry door that installs smoothly, seals tightly, and enhances curb appeal, you can select an entry door that installs smoothly, seals tightly, and enhances curb appeal. That is the goal of any well-done entry door measuring project.
FAQs about Entry Door Measurement
Q1. Do I need a permit to widen an entry opening?
If you change the width, height, or structure, a permit is usually required. Enlarging the rough opening often needs a new, properly sized header and an inspection. Like-for-like replacements may be exempt. Always confirm with your local building department first.
Q2. How do I measure for adding sidelites or a transom?
Measure the total rough opening you plan to frame, not the old slab size. Include the mull post thickness and required clearances. For transoms, verify header height and trim space above. Use three location readings and keep the smallest dimensions.
Q3. What clear opening supports accessibility or aging in place?
Target at least 32 inches of clear passage with the door at 90 degrees. Many homes select a 36-inch slab to achieve that. Offset hinges can add up to about 1.5 inches. Verify local code and mobility turning space before ordering.
Q4. How do I measure for a storm door with my entry door?
Record brickmould width and thickness, jamb reveal depth, and check straightness at head and sides. Confirm your handle projection clears the storm frame. Measure inside the brickmould at top, middle, and bottom, use the smallest, and note the sill shape for adapters.
Q5. What measurement accuracy should I submit?
Use a steel tape and record to the nearest 1/16 inch. Take three readings and keep the smallest. Note out-of-level or out-of-plumb conditions, for example, 1/8 inch in 6 feet, and any sill hump. Avoid rounding up your numbers.
