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Allowance planner / trimming

How to trim a door without guessing the allowance

Measure the current leaf and the opening, choose the intended gaps, then enter the manufacturer’s separate limit for the left, right, top and bottom edges. If the required removal exceeds the entered limits, stop: do not mark or cut the leaf.

Door edge allowance diagramA door leaf outline. Cut lines appear only after a current calculation produces a complete trimming plan.LEFTRIGHTTOPBOTTOM
Each edge is independent. Lines appear only for positive allocations in a complete current plan and disappear on edit, stop or failure.

The Marked Door · Planning worksheet · How to trim a door without guessing the allowance

Four-edge allowance record

Compare required removal with entered limits

Formula v1.0.0Researched 2026-09-04

1. Current leaf and opening (mm)

Measure the leaf itself and the available opening at the same stage of the job. Do not substitute a catalogue nominal size.

Worked example — default entered values

No cut plan in this worked example

A 770 × 1990 mm leaf in a 766 × 1992 mm opening with L2/R2/T2/B6 mm gaps needs 8 mm removed across its width. The entered L3/R3 mm side limits total only 6 mm.

Entered-value register

Fire door: no. Current leaf: 770 × 1990 mm. Opening: 766 × 1992 mm. Entered gaps L 2, R 2, T 2, B 6 mm. Manufacturer limits L 3, R 3, T 2, B 6 mm.

The planner subtracts entered gaps from the entered opening and then compares removal with the paired limits. It does not assess the door’s construction, condition, certification, finish or warranty terms.

The Marked Door / stopped worked example
Job/reference: ____________________ · Printed date: ____________________
Canonical: https://neoporte.com/trim-a-door/ · Module 1.0.0 · Research date 2026-09-04 · Sources: jeldwen-trimming, jeldwen-trimming-warranty, gov-fire-door

2. Entered final gaps (mm)

These are project inputs, not defaults supplied by this page. Zero is accepted when it is genuinely the entered requirement.

3. Mandatory manufacturer limits for all four edges (mm)

Read the exact instructions for this door. Enter each edge separately, including a zero where that edge must not be trimmed. Never copy one allowance across the other edges unless the same instructions expressly state it.

4. Is this a fire door, or could it be one?

Current-result print becomes available only after a complete current no-trim record or trim plan. Editing any answer withdraws it immediately. The blank sheet is a separate print mode.

Before a cutting tool

Confirm what is moving and what is fixed

Record each face, edge and orientation, then recheck the opening at more than one position. A narrow point does not prove the whole leaf should become that width. Check hinges, screws, stops, seals, floor finishes and latch alignment before treating contact as excess material. If the door has moved, the measured requirement may change; the door symptom checker starts with those observations.

Take the intended four gaps from the project information; this planner supplies no universal gap. If the leaf is already smaller than the entered target, the outcome is undersized and removing material cannot resolve that axis.

Method / 1.0.0

The arithmetic before distribution

target width = opening width − left gap − right gapwidth removal = current width − target widthtarget height = opening height − top gap − bottom gapheight removal = current height − target height

Each removal is compared with the sum of the two entered limits on its axis. A positive amount is split as evenly as those two limits permit. Zero removal and zero limits are valid entries. Negative removal means the leaf is undersized for the entered target and returns no plan.

Why distribution is constrained

An even split is a neutral calculation, not a claim that both edges are interchangeable. If one edge reaches its entered limit, the remainder moves only when the other entered limit can contain it. If a paired total is too small, the complete operation stops; no width or height portion is published alone.

Keep the record with the actual product instructions. The JELD-WEN source record demonstrates only the scoped point that allowances vary with door construction and instructions; it is not an allowance for another make or model. Read the trimming source note.

Fixed worked example

Why the default example stops

The current leaf is 770 mm wide and 1990 mm high. The opening is 766 mm wide and 1992 mm high. Entered gaps are 2 mm left, 2 mm right, 2 mm top and 6 mm bottom. That gives a target of 762 × 1984 mm: width removal is 8 mm and height removal is 6 mm.

The entered limits are 3 mm left, 3 mm right, 2 mm top and 6 mm bottom. Height could fit its paired total, but width exceeds the 6 mm side total. The whole calculation stops with no allocation or cut lines; no partial plan survives.

If the opening width were 774 mm with the same side gaps, the width target would be 770 mm and removal zero. That is a no-trim outcome for that axis, not an instruction about final fit.

Tool and surface planning

Plan the cut, dust and tear-out controls together

Identify the door construction and finish before choosing a method. Support the leaf flat, protect both faces, keep hands clear of the tool path, mark from the retained size and remeasure before the first pass. Tear-out often begins where a cutter exits; backing, a scored line or a fine finishing pass may help, but technique depends on the actual tool and material. Test comparable waste when practical.

Plan extraction, ventilation, eye and respiratory protection for the material and tool. Keep others away. For controlled reduction on a timber edge, compare a cordless power planer for hire against the door instructions. An in-situ bottom cut after a flooring change uses a different door trimming saw for hire; its listed 10–65 mm depth does not match every allowance. Check construction, entered limits and current tool instructions before choosing either.

Contextual next steps

Keep measuring, reference and diagnosis separate

These routes record or explain the next decision; none supplies a trimming permission or product choice.

Dated source register

Sources used for the stop rules and scope

The arithmetic is stated in full on this page. No external source is presented as a universal trim allowance. Source access and research date: 2026-09-04.

Blank four-edge worksheet

Record the product instruction beside every edge

Job/reference: ____________________ · Door/product reference: ____________________ · Printed date: ____________________

RecordLeft / widthRight / heightSource or position note
Current leaf
Opening
Entered gaps
Manufacturer edge limits
Calculated removal / stop

Fire door: yes / no / not sure   Product instructions checked: ____________________

Canonical: https://neoporte.com/trim-a-door/ · Module 1.0.0 · Research date 2026-09-04 · Sources: jeldwen-trimming, jeldwen-trimming-warranty, gov-fire-door