A 10 ft floor-to-floor stair with a quarter-turn landing halfway takes 16 risers of 7½ in: 8 up to a 36 × 36 in landing that sits 5 ft above the floor, then 8 more. With 10 in treads each flight runs 5 ft 10 in, and the L-shaped stair fits in an 8 ft 10 in square. The same stair built straight through the landing needs 14 ft 8 in of length; as a U with a 4 in gap it fits in 8 ft 10 in by 6 ft 4 in.
How the stair with a landing is calculated
The landing does not change the risers. The whole rise is divided into equal risers exactly as on the stair calculator, because IRC R311.7.5.1 limits the difference between risers within a flight to ⅜ in and the landing is simply one of the steps. The calculator then splits the risers between the two flights, half and half unless you set the number below the landing.
Landing height = risers below the landing × riser height. Each flight's run = (its risers − 1) × tread depth.
Each flight loses one tread to the surface it arrives on: the lower flight's last step is the landing, the upper flight's last step is the floor. So 16 risers give 7 + 7 = 14 treads plus the landing.
The footprint depends on the turn:
- Straight: lower run + landing depth + upper run, one stair width wide. 70 + 36 + 70 = 176 in.
- L, quarter turn: (lower run + landing) by (stair width + upper run). (70 + 36) × (36 + 70) = 106 × 106 in.
- U, half turn: (the longer run + landing) by (two stair widths + the gap). (70 + 36) × (2 × 36 + 4) = 106 × 76 in.
How big does a stair landing have to be?
IRC R311.7.6 asks for a floor or landing at the top and bottom of every stair, at least as wide as the stair it serves. On a straight run it must be at least 36 in deep in the direction of travel. Where the stair turns, the landing has to be as wide as the flight leaving it, so a 36 in stair gets a landing at least 36 × 36 in, and a U-turn landing spans both flights and the gap: 36 × 76 in for the example. Wider stairs grow the landing with them: a 42 in stair needs a 42 in landing.
The Saint Paul building department's handout and the American Wood Council's DCA 6 deck guide say the same: landing width no less than the stair, and 36 in minimum in the direction of travel.
When a landing is required
| Rule | Limit | Source |
|---|---|---|
| Rise of one flight | 12 ft 7 in max between floors or landings | IRC R311.7.3 |
| Deck stair height | Over 12 ft 0 in needs an intermediate landing | AWC DCA 6 |
| Cut deck stringer span | 6 ft horizontal, then a post or a landing | AWC DCA 6 Fig. 28 |
| Landing depth, straight run | 36 in min | IRC R311.7.6 |
| Landing width | Not less than the stair width | IRC R311.7.6 |
A 14 ft rise, for a tall basement or a two-story deck, is one example: 22 risers of 7 ⅝ in cannot go up in one flight because 14 ft is more than 12 ft 7 in. Split 11 and 11, each flight rises 7 ft.
Stair calculator with landing turn: L or U?
An L-shaped stair turns 90° at the landing and fits into a corner; the upper flight starts from the side of the landing. A U-shaped stair turns back on itself, so both flights share one wall and the stair takes little more length than a single flight. The gap between the flights is yours to choose: a few inches for a handrail, or a full wall.
Moving the landing changes the footprint. With 10 risers below and 6 above, the L becomes 10 ft 6 in by 7 ft 2 in instead of a square. Set "Risers below the landing" to match where the landing has to sit, for example under a window or above a door.
Headroom and framing
Each flight needs 6 ft 8 in of headroom above its nosing line (IRC R311.7.2), which the stair calculator checks for a single flight. The landing itself is a small floor: framed like a deck platform outdoors, or a box of joists indoors, with its finished surface at the landing height shown. Cut the stringers for each flight with the stair stringer calculator; the material list gives each flight's stringer length.
Related calculators
- For a stair in a tight square footprint, compare with the spiral staircase calculator.
- Deck stairs with a landing: plan the deck with the deck calculator.
- Poured steps up to the landing: the concrete steps calculator.