Getting the inputs right before you calculate
A landing check only takes three real-world numbers — the calculator does the rest. Get these three right and the result is trustworthy.
Measure the stairway's clear width
Measure wall-to-wall (or handrail-to-handrail, whichever is narrower) at the top or bottom of the flight where the landing attaches. This is the number the landing width almost always has to match or exceed.
Note whether a door lands here, and which way it swings
Stand at the landing and watch the door open. "Swings over the landing" means the door leaf sweeps into the landing's floor area — not just toward it. A door that swings back into an interior hallway does not swing over the stair-side landing.
For exterior doors, measure the threshold step
Measure straight down from the top of the door threshold to the finished surface of the landing or deck below. This is the number most homeowners never check until the final inspection.
Read the compliance chips
Green means the dimension you entered meets IRC residential minimums. Red means the landing, as planned, needs to grow — or the threshold step needs to shrink — before you frame it.
The four rules behind every result
Nothing on this page is a black box. Here's exactly what runs when you change a number.
Landing Width
The landing can never be narrower than the stairway it serves — and if a wider door lands there, the door governs instead.
Landing Depth
A flat code minimum. Unlike width, it does not scale up with a wider stairway — a 60" wide stair and a 36" wide stair both need only 36" of depth.
Exterior Threshold Step
How far the landing can sit below the top of an exterior door's threshold — the limit changes depending on whether the door sweeps over that drop.
Landing Area
The minimum clear floor area the landing has to provide, useful for framing takeoffs and material estimates.
Walking through a 38" basement stair with a top door
Same four rules, filled in step by step, for an interior basement stair with a door at the top landing — the default this calculator loads with.
Start with stairway width
The stairway is 36" wide, so the landing's baseline width requirement is 36". That number alone would satisfy code if there were no door here.
Check whether the door changes it
A 36" door sits at the top landing. Since the door width (36") is not greater than the stair width (36"), the requirement stays at 36". If this were instead a 42" oversized door on the same 36" stair, the door would govern and push the requirement up to 42" — the wider of the two rules always wins, not the stairway width by default.
Apply the flat depth minimum
Regardless of the 36" width just calculated, depth is a separate, non-scaling rule: 36" minimum, measured in the direction someone walks through the doorway. A wider stairway does not relax or tighten this number.
Confirm the door has room to swing
Because the door swings over this landing, the full 36" of depth has to be clear of obstructions through the door's swing arc — a wall-mounted light fixture or a handrail return that intrudes into that 36" effectively fails the check even if the slab itself is poured to size.
Total minimum area
36" × 36" = 1,296 sq in, or 9 sq ft — the smallest clear rectangle this landing can be poured or framed to.
This is why entering only the stairway width and skipping the door fields understates the requirement whenever the door is the wider of the two — always fill in the door width if one exists, even a standard 36" door, so the calculator can compare it against the stair.
Landing dimension code reference, quick comparison
This calculator checks your result against the residential (IRC) figures below by default. Commercial (IBC) figures are shown for reference — verify the exact clause with your local plan reviewer before relying on them.
| Requirement | Residential (IRC) | Commercial (IBC) |
|---|---|---|
| Min landing width | ≥ width of stair or door | [VERIFY: confirm current IBC minimum landing width — commonly cited around 44"] |
| Min landing depth (direction of travel) | 36" | [VERIFY: confirm current IBC minimum landing depth and any 48" straight-stair cap] |
| Max threshold step, door swings over | 1.5" | [VERIFY: confirm IBC/accessibility threshold limit for the applicable occupancy] |
| Max threshold step, door doesn't swing over | 7.75" | [VERIFY: commercial exterior door threshold exception, if any] |
| Door-swing encroachment limit | no reduction below min. dimension | ≤ half of required width, per leaf |
Reference only — always confirm against your local jurisdiction's adopted code before building. IRC figures reflect IRC 2021 Sections R311.3 and R311.7.6.
Doors, thresholds & the top-of-stair exception
A landing can pass the width and depth check and still fail inspection on one of these three items — all specific to how a door interacts with the platform beneath it.
The top-of-stair exception
IRC allows an interior flight to start right at a door threshold — skipping a formal landing — only when that door swings away from the stairs, not over them. Confuse "over the stairs" with "over the landing" and you can talk yourself into an exception that doesn't apply.
Exterior threshold elevation
This is the single most commonly missed item on exterior landings. A poured patio slab that ends up 3" below the threshold passes every width and depth check and still fails if the door swings out over it.
Door-swing encroachment
Even when the landing meets its minimum dimensions on paper, a door swinging fully open has to clear that space without hitting a railing, a wall return, or a second door swinging the opposite way — check this physically, not just on the drawing.
Irregular-shaped landings
A non-rectangular landing — an angled or pie-shaped platform at a turn — still has to provide the full minimum dimension measured along the actual path of travel, not just somewhere within its overall footprint.
These are planning-stage checks, not a substitute for your local plan reviewer's sign-off, especially where accessibility (ADA/ANSI A117.1) requirements layer on top of the base building code.
Common mistakes when sizing a landing
Most landing rejections at inspection trace back to one of these five planning errors, not to bad concrete or framing work.
Sizing to the stair only, ignoring a wider door
Landing width is the greater of the stairway width or the door width serving it — a standard 36" door on a 34" stair sets the requirement at 36", not 34".
Assuming depth scales with stair width
The 36" depth minimum is flat. Widening the stair does not widen the depth requirement, and narrowing it below 36" of stair width does not shrink the depth requirement either.
Mixing up "over the stairs" and "over the landing"
The top-of-stair no-landing exception only applies when the door doesn't swing over the stairs themselves — a door swinging over an already-present landing doesn't disqualify the exception at the bottom of that same door's own threshold logic, but it does trigger the separate threshold-elevation check.
Skipping the threshold check on exterior doors
This is the item most often missed because it isn't obviously part of "landing size" — a correctly sized slab still fails if it sits too far below the door threshold.
Building an irregular landing without confirming both dimensions
An angled or pie-shaped landing at a stair turn needs the full minimum width and depth along the actual travel path, not just as an average across an oddly-shaped footprint.
When to use a landing size calculator
Landing sizing shows up early in almost every stair or entry-door project, indoor or out.
Basement Stair Remodel
Confirming the new top landing clears code before framing the opening.
Exterior Door Replacement
Checking threshold elevation on a new door against the existing exterior grade or deck.
New Construction Plan Review
Sizing every stairwell landing box before the plan set goes to permit.
Deck Stair Landing
Confirming the landing pad at grade meets minimum size before pouring concrete.
Accessibility & Egress Doors
Planning door-swing clearance at an accessible entry before finalizing hardware.
Permit & Plan-Check Prep
Catching an undersized landing before a reviewer or inspector catches it first.