Key takeaways
- A replacement door is ordered from the leaf's own dimensions; the frame opening is a separate record.
- Hinge preps are located top-to-top: from the top edge of the leaf to the top of each hinge mortise.
- Hinge weight is leaf thickness, not mass; a 4-1/2 inch hinge runs about 0.134 inches standard and 0.180 inches heavy.
- Backset is measured from the lock edge to the actuating centerline, on the wide face of a beveled door.
- Frame openings are measured rabbet to rabbet at three points, and the smallest reading controls sizing.
- Photograph door and frame labels before ordering; a fire-rated opening is a stop-and-verify condition.
First principle
The order is written from the leaf, not the opening.
A replacement commercial door is manufactured to the dimensions of the door leaf itself, not to the size of the hole it hangs in. The most common wrong-door order starts when someone measures the frame opening, or folds the old door's clearances into its width, and writes the result down as the door size. The Steel Door Institute's replacement-door practice treats leaf dimensions and frame dimensions as separate records for exactly this reason.
The convention that prevents those orders is simple: call the datum before reading the tape. Every number on a door survey should name its reference point, whether that is the top edge of the leaf, the lock edge, the wide face, or the frame rabbet, before the measurement is recorded. A dimension without a stated datum cannot be checked later, and a supplier cannot safely build from it.
Leaf dimensions
How do you measure net width, height, and thickness?
Net leaf size is three numbers, each read directly from the door: width, height, and thickness. None of them are inferred from the frame, the old paperwork, or another door on the property.
| Measurement | Reference | Recording rule |
|---|---|---|
| Net width | Edge to edge across the wide face of the leaf | Use the wide face of a beveled door; do not add clearances to the number |
| Net height | Top edge to bottom edge of the leaf | Record undercut separately; it is a site condition, not part of leaf height |
| Thickness | A clear, undamaged section of the door edge | Measure it directly; never infer it from the frame stop or old records |
| Hinge preps H1–H4 | Top edge of the leaf to the top of each hinge mortise | Number hinges from the top down; record hinge height, width, weight, and corner |
| Lock centerlines | Top edge of the leaf to each actuating centerline | Record lever and deadbolt preparations as separate entries |
| Backset | Lock edge of the door to the actuating centerline | Read it on the wide face of a beveled door |
| Frame opening | Rabbet to rabbet, width and height | Measure at three points; the smallest reading controls sizing |
Hinge preps
How do you record hinge locations and hinge weight?
Replacement-door convention numbers the hinges from the top down, H1 through H4, and locates each one by measuring from the top edge of the leaf to the top of that hinge mortise. Top-to-top measurement keeps every hinge prep tied to the one edge of the door that does not change with flooring, thresholds, or settling.
Location is only half the record. Each hinge prep also needs the hinge height, width, corner style, and weight, because the mortise is cut to match all four. A square-corner mortise will not accept a radius-corner hinge cleanly, and an undersized mortise leaves the hinge sitting proud of the edge.
Hinge weight means the thickness category of the hinge leaf, not its physical mass. For a 4-1/2 inch commercial hinge, approximately 0.134 inches is standard weight and approximately 0.180 inches is heavy weight. A door prepped for one will not seat the other flush: the hinge sits above or below the edge plane, and the mismatch surfaces later as alignment and latching problems that look like lock failures.
Lock preps
How do you locate lock centerlines and backset?
Each lock preparation is located from the top edge of the leaf to its actuating centerline, and each device is its own entry. A lever and a deadbolt on the same door are two separate centerlines, not one combined note; collapsing them into a single dimension is how a replacement door arrives with the deadbolt prep in the wrong place.
Backset is the horizontal dimension: from the lock edge of the door to the actuating centerline. On a beveled door it is read on the wide face. Measuring from applied trim or an escutcheon edge instead of the true lock edge is the common way this number goes wrong.
Suppliers cut these preparations to published definitions; ANSI/SDI A250.14 is the hardware-preparation reference for standard steel doors and frames. A survey that names its datums lets the order be checked against those definitions before anything is manufactured.
Frame check
Why are leaf and frame dimensions separate workflows?
The frame gets its own measurements: opening width and height, taken rabbet to rabbet, each at three points. The smallest reading controls sizing, because a door sized to the widest point of a racked frame will bind at the tightest one.
Frames move. Buildings settle, anchors loosen, and years of traffic leave a frame slightly out of square, so a single mid-height width reading can be wider than the reading at the head or near the floor. Three readings in each direction expose that condition before it becomes a fit problem.
Keeping frame dimensions on separate lines from net leaf size is what makes the survey usable. A record that mixes the two produces either a door that binds or a door with oversized gaps, and neither failure is visible until the new leaf is already hanging.
Survey record
What should be photographed and identified before ordering?
Dimensions alone do not make a complete survey. Before a replacement door or major hardware order, expect the record to cover four more categories.
Identity and labels
Door ID or mark, material, thickness, handing, and whether the opening is interior or exterior. Photograph the door and frame labels and record the fire rating and any smoke or temperature-rise marks. On a rated opening, ordering pauses until the listing and approval path are confirmed.
Existing hardware
Make, model, function, trim, strike, finish, and any electrification. Photograph both faces of the opening, the door edge, the frame prep, the closer, any exit device, and visible wiring. Replacement hardware is selected from this record, not from what looks similar on a shelf.
Cutouts
Any lite or louver is recorded by its width and height and located from two edges, the top and the lock edge, along with the rails and stiles around it. Note the visible glass, insert finish, glass or louver type, and its listing.
The request itself
The new hardware type, finish, grade, brand, and, where electrified hardware is involved, voltage and fail state. Damage, missing reinforcement, conflicts, and open approval questions belong on the order before it is placed, not discovered after delivery.
Approval gate
The before-ordering checklist.
Before approving a replacement-door order, confirm the survey record shows all of the following. A missing line here is often the difference between an installation and a return shipment.
When any item is unclear, the correct sequence is the one a careful installer follows: photograph the condition, protect the opening, and stop until the question is answered. On fire-rated, egress, or accessible openings, approved plans, product listings, manufacturer instructions, adopted code, and the authority having jurisdiction control what may be ordered and changed.
- Door and frame labels photographed, visible, and legible
- Net leaf width, height, and thickness recorded separately from the frame-opening dimensions
- Every hinge located top edge to top of mortise, with hinge size, weight, and corner recorded
- Lever and deadbolt preps recorded as separate centerlines, with backset measured from the lock edge
- Lite and louver cutouts located from two edges
- Existing hardware identified by make, model, and function
- Listing and management approval confirmed for any rated or previously modified opening
Common questions
Questions about measuring commercial replacement doors
Can a replacement door be ordered from the frame opening dimensions?
No. The manufacturer builds the door to the net leaf dimensions, so the leaf is measured directly: width edge to edge on the wide face, height from top edge to bottom edge, and thickness at a clear edge. The frame opening is measured separately, rabbet to rabbet at three points, and is used to check the frame, not to size the leaf.
What does hinge weight mean on a door survey?
Hinge weight describes the thickness of the hinge leaf, not how heavy the hinge feels. For a common 4-1/2 inch commercial hinge, approximately 0.134 inches is standard weight and approximately 0.180 inches is heavy weight. The door's hinge mortises are prepped for one or the other, so the survey records weight along with hinge height, width, and corner.
Which face of a beveled door should be measured?
The wide face. Most commercial doors are beveled slightly at the lock edge so the door can swing past the frame stop, which makes one face slightly wider than the other. Net width and backset are both read on the wide face; measuring the narrow face understates the dimension and can produce a door that fits poorly at the strike.
Why is the threshold or undercut never used as a measuring reference?
Because it moves. Undercut changes with flooring work, threshold swaps, and site conditions, so any dimension referenced from the floor drifts over the life of the opening. Hinge and lock preps are located from the top edge of the leaf, and undercut and threshold conditions are recorded as their own entries rather than folded into a prep dimension.
What should be photographed before a replacement door is ordered?
Both faces of the opening, the door edge, the frame preps, the closer, any exit device, visible wiring, and every door and frame label. The label photos matter most: they establish the fire rating and any smoke or temperature-rise marks, which determine whether the opening can be modified at all without a confirmed listing and approval path.
Sources and further reading
These references support the general technical guidance. The right answer for a specific opening still depends on the property and the authorities responsible for the project.