L-shaped stair calculator

Start with the same riser math as any stair: divide total rise by target riser height, round to the nearest whole number, then divide back for the exact riser height. A 108 in rise at a 7.25 in target gives 15 risers at 7.2 in each.

Pick how many of those risers happen before the turn. A lower flight of 4 risers has 3 treads and a run of 3 × 10.5 = 31.5 in. The remaining 11 risers make the upper flight, with 10 treads and a run of 10 × 10.5 = 105 in.

The landing sits at the corner where the two flights meet, turned 90 degrees from each other, so someone walking up climbs the lower flight, turns a quarter turn on the flat landing, then climbs the upper flight in a new direction.

Because the flights are perpendicular, the L-shaped stair's footprint isn't one long rectangle, it's two legs meeting at a corner, like an L. Leg one is the lower flight's run plus the landing depth; leg two is the landing depth plus the upper flight's run.

With a 31.5 in lower run and a 36 in landing, leg one is 31.5 + 36 = 67.5 in. With a 105 in upper run and the same 36 in landing, leg two is 36 + 105 = 141 in. Those two legs, plus the stair width on each, define the total floor area the stair consumes.

This is why an L-shaped stair often fits better in a corner room than a straight or landing stair of the same total rise: the two legs can each hug a different wall instead of demanding one long straight wall.

Placing the landing low, mid-flight, or high changes each leg's proportions without changing the total riser count. A low landing (few risers before the turn) makes the first leg short and the second leg long; a high landing does the opposite.

Mid-flight placement, roughly splitting the risers in half, tends to balance the two legs and often looks the most intentional in a floor plan. But the right placement is usually decided by where the turn needs to land relative to a door, window, or structural wall, not by symmetry alone.

1. Calculate total risers and riser height for the full rise.
2. Choose the lower flight's riser count based on where you want the turn.
3. Subtract to find the upper flight's riser count.
4. Calculate each flight's tread count (risers minus one) and run.
5. Add landing depth to each flight's run to get that leg's footprint length.

A square landing and a set of winder treads both turn a stair, but they use floor space differently. A landing needs a full flat platform at least as deep as the stair is wide, while winders replace that flat spot with pie-shaped treads that turn gradually through the corner.

Landings are generally considered more comfortable and give you a place to pause, but they take up more floor area. Winders save space but narrow sharply on the inside of the turn. If your L-shaped layout doesn't have room for a full landing, compare it against the winder stair calculator before committing to the L-shape.

Headroom needs checking at the landing itself, not just along each straight flight, because framing above the landing (like a floor joist or header from the level above) can cut into clearance right where people naturally slow down to turn.

Commonly cited residential reference values call for at least 6 ft 8 in of headroom measured vertically from the nosing line, and that clearance needs to hold through the landing and the first few steps of the upper flight, not just the lower flight. If the upper flight's stairwell opening was sized for a straight run, double-check it after adding the turn.

An L-shaped stair works well when the entry or stairwell is in a corner, when you want a landing to break up a tall rise, or when the direction of travel needs to change to line up with the rooms above and below. If you need a full 180-degree reversal instead of a 90-degree turn, use the U-shaped stair calculator, which handles the wider landing that reversal requires.