How to measure an existing frame before ordering custom wooden doors

Ordering Custom Wooden Doors for an existing frame starts with measuring the opening where the new door will sit. The old door provides useful clues, but copying its dimensions can reproduce an existing problem: an uneven gap, a dragging bottom edge, or a latch that only catches when the handle is lifted.

Record the frame’s actual dimensions before calculating the finished door size. Measure width and height in several places, check whether the frame is square and straight, and document the hinges, lock, and floor clearance. Your manufacturer needs to know which figures describe the opening and which describe the door you want made.

Check whether the existing frame is suitable

These instructions apply to a hinged replacement door leaf fitted into a retained frame. If you are replacing the frame as well, the manufacturer will need measurements for the structural opening and the complete door assembly.

Before measuring, inspect the hinge jamb, latch jamb, and head jamb—the two vertical sides and the horizontal top of the frame. Look for loose fixings, split timber around hinges, soft or decayed areas, and joints that have opened. A frame that moves when the door operates needs repair before its dimensions can serve as a reliable manufacturing reference.

Observe how the existing door closes. Rubbing near the upper latch corner may relate to hinge movement or frame distortion. A bottom edge scraping the floor may result from sagging, insufficient clearance, or a raised floor finish. These symptoms help identify what needs attention; they do not automatically mean the replacement should be smaller.

For a fire-rated or smoke-control opening, establish the permitted replacement specification before ordering. The door, frame, seals, hinges, and other hardware work together, so physical fit alone does not establish suitability.

Identify the surfaces you need to measure

Use a reliable tape measure, a spirit level, a long straightedge, and a square. A helper makes diagonal measurements easier. Draw a simple sketch and record every measurement in one unit, without rounding figures to a familiar standard door size.

The frame opening is the space between the jamb surfaces that will surround the closed door’s edges. Measure at the depth where the door leaf will sit. The decorative trim around the doorway is not a measuring reference.

Many frames have a projecting stop that the closed door rests against. Others have a rebate—a step formed in the frame to receive the leaf. Do not measure between the projecting edges of the stops: that gives the narrower passage opening rather than the space available for the door. On a rebated frame, identify the surfaces surrounding the leaf and show their position in your sketch.

Keep these dimensions separate:

• Frame opening: the measured space available for the leaf, before fitting clearances are deducted.
• Finished leaf size: the required manufactured width, height, and thickness of the door itself.
• Overall frame size: the outside dimensions of the frame, which normally do not determine a replacement leaf’s size.

If the supplier’s order form uses terms such as “opening size,” “rebate size,” or “order size,” agree on exactly which surfaces those terms describe before submitting dimensions.

Measure width and height at several points

Record three widths

Measure horizontally between the side jambs near the top, around the middle, and near the bottom. Keep the tape straight and at the same depth within the frame for each reading. Label the measurements individually rather than averaging them.

The narrowest reading identifies a possible restriction, but it is not automatically the finished door width. The leaf also needs operating gaps at the hinge and latch sides. Those gaps depend on the frame condition, door construction, hardware, finish, and intended use.

Check each jamb with a straightedge. A local bow can restrict the opening between your measuring points, even when the top, middle, and bottom readings appear consistent. Record the location of any inward bow so the installer can assess whether the frame needs adjustment.

Measure height on both sides and through the middle

Measure from the underside of the head jamb to the finished floor or threshold at the hinge side, center, and latch side. Use the head surface above the leaf, rather than the lower edge of a projecting stop.

Record what forms the lower reference: tile, timber flooring, carpet, or a threshold. If flooring is being replaced, the future finished level must be included in the door-sizing decision. Measuring to an exposed subfloor and forgetting the new finish can leave the door too tall.

For an exterior doorway with a bottom seal, document the threshold profile and the existing seal arrangement. The required relationship between the leaf, seal, and threshold affects both door height and machining.

Check square, level, and the path of the swing

Measure diagonally across the opening in both directions, using matching corner references at the same depth. A difference between the diagonals indicates that the opening is out of square. Record both readings instead of noting only “frame uneven.”

Diagonal measurements do not reveal every problem. Use the level to check both jambs for plumb and the head for level. A straightedge helps reveal bowing. Also check whether the frame is twisted: a door may fit its width and height yet contact the stop at one corner before it reaches the stop elsewhere.

Small irregularities may be manageable during fitting. More pronounced distortion can require frame adjustment or repair. Making a rectangular door small enough to pass through a distorted opening can leave conspicuous gaps without correcting the underlying alignment.

Next, inspect the floor throughout the door’s swing. The floor directly beneath the closed leaf may be lower than the floor farther into the room. A door can therefore clear the floor when closed and scrape as it opens. Include planned flooring changes and any permanent obstruction within the swing area.

Bottom clearance also needs to suit the opening’s purpose. Carpet, ventilation requirements, acoustic seals, and threshold seals can affect the decision. Agree on that clearance as part of the specification rather than applying one deduction to every doorway.

Record thickness, hinges, and the lock position

Accurate width and height will not make a replacement door fit if its hardware preparation is wrong. This matters especially when the new leaf will arrive with hinge recesses and lock machining already completed.

Measure the old door’s thickness at a sound, accessible edge, avoiding raised moldings or damaged areas. Then check how that thickness relates to the frame rebate or stop position. A thicker replacement may interfere with the stop or change hinge alignment; a thinner one may sit incorrectly against seals.

Use one clear reference for hinge positions

For each hinge, record its height, leaf width, thickness, corner shape, and recess depth. Include the number of hinges and any identifying hardware information. Photograph unusual hinges and show their position relative to the door face.

Measure each hinge position independently from one consistent reference, normally the top edge of the door to the top of each hinge recess. Avoid measuring from one hinge to the next, because an early error then carries through the remaining positions.

If measuring the frame recesses, label those dimensions as frame measurements. The distance from the underside of the head jamb to a frame hinge recess includes the top operating gap; the corresponding distance measured from the door’s top edge does not. Mixing these references can shift every hinge position.

A heavier or differently constructed wooden door may require a revised hinge arrangement. Existing recesses show where the old hardware sits, but do not by themselves establish that the same hardware will support the replacement.

Document the latch and lock preparation

Record the handle or spindle center height from a stated reference, the latch position, and the dimensions of the lock faceplate. For a bored lock, include the bore sizes and backset—the distance from the door edge to the handle or cylinder centerline. For a mortise lock, the manufacturer also needs the lock case and pocket details.

Show the strike plate’s position in the frame. Reproducing the old door’s lock height can preserve poor alignment if the old latch already catches badly. Establish whether the strike will remain in place or be repositioned before machining the new leaf.

Describe the opening direction with a sketch showing the hinge side and direction of swing from a named viewpoint, such as the hallway. Handing terminology varies between suppliers, so a drawing removes ambiguity.

Convert opening measurements into an agreed door size

Send the manufacturer the raw frame measurements before agreeing on the finished leaf dimensions. Ask who will calculate the operating gaps and whether the supplied size includes allowances for finishing and site fitting.

Avoid deducting clearance yourself and then submitting that result as an “opening size.” If the manufacturer makes another deduction, the finished leaf may be undersized.

Custom wooden doors also differ in how much adjustment they permit. Solid timber, engineered timber, and veneered constructions can have different trimming limits. Edge lippings, internal components, glazing, and prepared hardware positions may restrict where material can be removed. Establish the permitted trimming allowance before relying on installation adjustments.

Finishing matters too. If the leaf will be painted or sealed after delivery, agree on whether the manufacturing dimensions allow for the specified finish. Timber responds to moisture conditions, so storage, acclimatization, and edge sealing should follow the supplied instructions. These measures support stable operation but cannot correct inaccurate frame measurements.

Send a measurement sheet that can be checked

Give every doorway a unique reference, especially when ordering several visually similar doors. Your submission should contain:

• The three widths, three heights, and both diagonal measurements, with measuring surfaces identified.
• Notes on bowed jambs, frame movement, floor slope, thresholds, and planned flooring.
• Door thickness, rebate or stop details, and the required finish.
• Hinge specifications and positions, with the measurement reference clearly stated.
• Lock, latch, strike, seal, and opening-direction details.
• Photographs of the complete opening and close views of relevant hardware.

Before production, review the dimensioned drawing or order confirmation against this sheet. Check that it distinguishes measured opening dimensions from finished leaf dimensions and shows the agreed clearances, hardware references, and swing direction. Once those details match the actual opening, the manufacturer has a clear specification for making the replacement.