Measure the height the stairs climb and the room they go in. You get an L or a U stair: each flight’s steps, the landing’s size and height, the floor it takes and whether it fits.
Your stairs
An L: 7 risers, a 36″ × 36″ landing, 7 risers14 risers of 7¹¹⁄₁₆″ on 12 treads · 11′ 3″ × 8′ 3″ of floor, the 36″ at its foot included · the landing 4′ 6″ up · meets the IRC
Quick answer: a landing where a stair turns is as wide as the stair in both directions (IRC R311.7.6): a 36″ stair turns on a 36″ × 36″ landing as an L, or on a landing 72″ across both flights as a U. A 9′ (108″) rise takes 14 risers of 7¹¹⁄₁₆″; as an L with the landing halfway, that is 7 risers, the landing, 7 risers on 11′ 3″ × 8′ 3″ of floor, against 14′ 5″ for the same stair straight.
How to use the stairs with a landing calculator
- Pick the shape: an L turns a quarter (90°) at the landing, a U turns back on itself (a switchback).
- Measure the total rise, finished floor to finished floor, and pick the tread depth, nosing to nosing.
- Enter the stair’s clear width: 36″ at least in a house. For a U, the gap between the two flights, if there is one.
- Enter the room, its length and width, to see whether the stair fits as drawn or turned a quarter.
- You get each flight, the landing’s size and height, the floor the stair takes and every other place the landing could go. Type a riser count in “Landing after” to move it.
The rules behind the numbers
The landing
“There shall be a floor or landing at the top and bottom of each stairway. The width perpendicular to the direction of travel shall be not less than the width of the flight served” (IRC R311.7.6). Where the stair turns, the flight arrives from one side and leaves from another, so the landing is that wide both ways: a square for an L, the width of both flights for a U. “Where the stairway has a straight run, the depth in the direction of travel shall be not less than 36 inches”, which is the floor kept at the stair’s foot.
Flights and steps
“A flight of stairs shall not have a vertical rise greater than 12 feet 7 inches (3835 mm) between floor levels or landings” (R311.7.3). Risers are 7¾″ at most and treads 10″ at least (R311.7.5), and the stair is 36″ wide (R311.7.1). The calculator divides the whole rise evenly, so the step onto the landing matches the rest. Headroom of 6′ 8″ is measured “from the sloped line adjoining the tread nosing or from the floor surface of the landing” (R311.7.2). Public buildings: risers 4–7″, treads 11″, a flight 12′ at most, stairs 44″ wide.
Winders instead of a landing
Winders turn the stair with tapered treads instead of a flat landing. The walkline “shall be located 12 inches (305 mm) from the inside of the turn” (R311.7.4); there, every winder is “not less than 10 inches (254 mm)” deep, and “not less than 6 inches (152 mm) at any point within the clear width of the stair” (R311.7.5.2.1). Treads that meet in a point at the inside corner fail the 6″, so winders are drawn full size or made by the stair maker.
Stairs with a landing by rise
A 36″ stair on 10½″ treads, the landing halfway (the lower flight takes the odd riser); the floor includes the 36″ at the stair’s foot:
| Total rise | Risers | Each riser | Flights | Landing height | L floor | U floor | Straight |
|---|---|---|---|---|---|---|---|
| 48″ (a deck) | 7 | 6⁷⁄₈″ | 4 + 3 | 2′ 4″ | 8′ 8″ × 4′ 9″ | 8′ 8″ × 6′ | 8′ 3″ |
| 72″ (a deck) | 10 | 7³⁄₁₆″ | 5 + 5 | 3′ | 9′ 6″ × 6′ 6″ | 9′ 6″ × 6′ | 10′ 11″ |
| 96″ (8′) | 13 | 7³⁄₈″ | 7 + 6 | 4′ 4″ | 11′ 3″ × 7′ 5″ | 11′ 3″ × 6′ | 13′ 6″ |
| 108″ (9′) | 14 | 7¹¹⁄₁₆″ | 7 + 7 | 4′ 6″ | 11′ 3″ × 8′ 3″ | 11′ 3″ × 6′ | 14′ 5″ |
| 120″ (10′) | 16 | 7¹⁄₂″ | 8 + 8 | 5′ | 12′ 2″ × 9′ 2″ | 12′ 2″ × 6′ | 16′ 2″ |
| 132″ (11′) | 18 | 7⁵⁄₁₆″ | 9 + 9 | 5′ 6″ | 13′ × 10′ | 13′ × 6′ | 17′ 11″ |
Four worked examples
Basement stairs, 9′ floor to floor, as an L. 14 risers of 7¹¹⁄₁₆″: 7 up to a 36″ × 36″ landing 4′ 6″ up, then 7 more. The stair takes 11′ 3″ × 8′ 3″ of floor, the 36″ at its foot included; straight it would be 14′ 5″ long.
The same stair as a U with a 4″ gap. The landing spans both flights: 76″ × 36″. The stair takes 11′ 3″ × 6′ 4″, two flights side by side.
The L in a 10′ × 10′ corner. With the landing halfway it needs 11′ 3″: too long. The most even place that fits is after 5 risers, 3′ 3″ up: 9′ 6″ × 10′.
Deck steps with a landing, 48″ up. 7 risers of 6⁷⁄₈″: 4 to a 36″ × 36″ landing, then 3 more, on 11″ treads. The steps take 8′ 9″ × 4′ 10″ of yard; straight they would be 8′ 6″ long. On a short stair a landing turns the steps; it does not save length.
Common mistakes with landings
- A landing narrower than the stair. A turning landing is as wide as the flight in both directions: 36″ × 36″ for a 36″ stair, more for a wider one.
- Forgetting the floor at the foot. The lower flight still needs its 36″ of floor in front of the first riser.
- A different riser onto the landing. Divide the whole rise evenly so the landing’s step matches every other.
- Headroom over the landing. 6′ 8″ is measured from the landing’s floor too, so a beam or soffit over it counts.
- Winders that meet in a point. Each must be 6″ deep at its narrowest and 10″ at the walkline, 12″ from the inside of the turn.
Your building department has the last word, and a stair usually needs a permit. Plan a straight stair with the stair rise and run calculator, add the handrail and guard with the railing height and baluster spacing calculator, and draw the rooms in the free 2D planner.
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Stairs with a landing questions
How big should a stair landing be?
As wide as the stair in both directions where it turns: 36″ × 36″ for a 36″ stair as an L, and as wide as both flights for a U (IRC R311.7.6). On a straight run, 36″ deep in the direction of travel.
What is the minimum stair landing size?
At a house, the landing is at least the stair’s width across and, on a straight run, 36″ deep (R311.7.6); the stair itself is 36″ wide (R311.7.1), so 36″ × 36″ is the smallest turning landing.
How do you calculate stairs with a landing?
Divide the total rise by 7¾″ and round up for the risers, as for a straight stair. Split them between two flights, with one less tread than risers in each: the landing replaces one tread. Add the landing, as wide as the stair both ways, and 36″ of floor at the foot.
How much space do L-shaped stairs need?
For a 9′ rise on 10½″ treads, 36″ wide, about 11′ 3″ × 8′ 3″ with the landing halfway, the 36″ at the foot included; moving the landing trades length for width.
What are switchback stairs?
A U-shaped stair: two flights side by side, turning back on a landing that spans both. A 9′ rise takes 11′ 3″ × 6′ of floor with 36″ flights and no gap between them.
What is the code for winder stairs?
Each winder tread is at least 10″ deep at the walkline, 12″ from the inside of the turn, and at least 6″ at any point within the stair’s width; at the walkline they match within ⅜″ (IRC R311.7.4, R311.7.5.2.1).
How high can stairs go without a landing?
12′ 7″ of rise in one flight at a house (R311.7.3) and 12′ in a public building; past that a landing splits the stair into flights.