How to Measure for a Custom Interior Door Slab

Why Accurate Measurements Matter

A custom door slab is built to your specifications. Unlike off-the-shelf doors, there is no returning to the store for the next size up. Taking the time to measure your finished opening correctly - and communicating those dimensions clearly at checkout - ensures your door arrives ready for your contractor to install with confidence.

This guide covers what to measure, how to record it, and how our ordering process works so your build goes smoothly from the start.

What You Are Measuring

We supply door slabs only. The jamb, casing, hardware, and installation are handled by your contractor. What we need from you are the finished opening dimensions - the width and height of the opening as it will exist after framing, drywall, and any finish work are complete.

The finished opening is the actual space the door slab will occupy, measured from the inside face of the jamb or finished frame on each side, and from the finished floor to the underside of the head jamb at the top.

What You Will Need

• A steel tape measure (cloth tapes can stretch and introduce error)
• A notepad or phone to record your measurements
• A helper is useful for taller or wider openings

Step 1: Measure the Width

Measure the width of your finished opening at three points: near the top, at the middle, and near the bottom. Record all three measurements. Use the smallest of the three as your finished opening width - this ensures the slab will clear the narrowest point of the opening.

Record your width in inches, to the nearest fraction you can reliably read on your tape measure.

Step 2: Measure the Height

Measure the height of your finished opening at three points: on the left side, at the center, and on the right side. Measure from the finished floor surface (or the top of any threshold, if applicable) to the underside of the head jamb or finished header above. Again, use the smallest of the three as your finished opening height.

Record your height in inches, to the nearest fraction you can reliably read.

Step 3: Note the Door Thickness

Standard interior door slabs are typically 1½” thick. If your project calls for a non-standard thickness - for example, a thicker slab for a heavier design or a specific hardware requirement - note this as well. If you are unsure, your contractor or hardware supplier can confirm what thickness is appropriate for your jamb and hardware selection.

Step 4: Understand How Hardware Affects Your Slab Size

Your finished opening dimensions are the starting point — but the actual slab size ordered will depend on your door type and the hardware system being used. This relationship varies and is not a fixed formula:

• Sliding (wall-mounted) doors require a slab that is larger than the finished opening in both width and height, so the panel fully covers the opening with the appropriate overlap. The exact amount added depends on the hardware selected.
• Bypass doors (interior or ceiling-mounted track) require panels that are larger than the finished opening in width to provide the correct overlap, but the height is typically reduced to account for the space the track system occupies above. Your hardware supplier can confirm the exact deductions for your chosen track.
• Multi-fold doors require panels sized to fit within the finished opening, with dimensions determined by panel count, track system, and pivot hardware requirements.
• Hinged swing doors require a slab sized precisely to fit within the jamb. Because clearances on the hinge side, latch side, top, and bottom depend on the specific jamb and hardware being used, your contractor should confirm the exact slab dimensions before you order.

We strongly recommend confirming your required slab dimensions with your contractor and hardware supplier before placing your order. Provide them with your finished opening dimensions and the hardware system you have selected, and they can confirm the exact slab size to order. Include those confirmed dimensions in your order notes at checkout.

Step 5: Note the Swing or Slide Direction

If your door will be a hinged swing door, note whether it is a left-hand or right-hand swing, and whether it swings toward you or away from you when opening. Your contractor will need this to prepare the jamb correctly, and it may affect how the slab is prepped for hardware.

For sliding, bypass, or multi-fold configurations, note the number of panels and the direction panels will stack or travel. If you are unsure which configuration is right for your space, our guide Sliding vs. Bypass vs. Multi-Fold Interior Doors: Which Is Right for You? covers each option in detail.

How to Place Your Order

Once you have confirmed your slab dimensions with your contractor and hardware supplier, here is how to order:

1. Find the closest whole-number size on our website. Browse our READYSHIP™ Door Collection or Custom Built options and select the listing with dimensions closest to your confirmed slab size.
2. Add your exact finished opening dimensions and confirmed slab dimensions in the order notes at checkout. Include width, height, thickness if non-standard, door type, swing or slide direction, and any other relevant details.
3. We review every order before building. Our team reads all order notes prior to cutting. If anything needs clarification, we will reach out before production begins.

A Note on Existing Door Replacements

If you are replacing an existing door, measuring the old slab is a useful starting point but should not be your only reference. Old slabs are often trimmed, warped, or sized to an opening that has since been modified. Always measure the finished opening directly rather than relying on the dimensions of the door you are replacing.

Ready to Order?

Start by browsing our READYSHIP™ Door Collection for slabs typically built within five business days, or explore our Custom Built options for non-standard dimensions, specific wood species, or unique design details. If you have questions before ordering, contact our team  - we are happy to help you confirm your measurements and find the right product for your opening.