What is a quarter-turn stair?

A quarter-turn stair is a staircase that changes direction by 90 degrees at a single turning point, usually a flat landing or a set of winder treads. It is functionally the same thing as an L-shaped stair, and the names are used interchangeably in residential construction.

Should I use a landing or winders for the 90-degree turn?

A landing is more comfortable, easier to build, and better for moving furniture, but it needs more floor space. Winders save space because the turn happens within the stair footprint, yet they are harder to lay out and less comfortable underfoot. For a primary stair, most builders and inspectors prefer the landing.

How do I calculate the total run of a quarter-turn stair?

Add three parts: the horizontal run of the first flight, the depth of the landing, and the horizontal run of the second flight. Each flight run equals its tread count times the tread depth. Forgetting the landing depth is the most common measuring mistake on these stairs.

How many risers should go in each flight?

First divide the total rise by your target riser height and round to a whole number of risers for the entire stair. Then split them between the two flights as evenly as your space allows. Every riser in both flights must end up exactly the same height to satisfy the 3/8-inch uniformity rule.

What is the minimum landing size for a quarter-turn stair?

The landing must be at least as wide and as deep as the stair flight it serves. Since residential stairs must be at least 36 inches wide, the landing needs a minimum depth of 36 inches too. A deeper landing is more comfortable and gives you room to maneuver furniture around the turn.

How do I check headroom at the turn?

Measure vertically from the nosing of each tread, including the treads under the upper flight where it crosses the lower flight or landing. You need at least 6 feet 8 inches of clear headroom at every point. Tight floor plans often fail this check right at the crossing, so verify it on paper before framing.

Do quarter-turn stairs need handrails on both sides of the turn?

Each flight needs a continuous handrail on at least one side, 34 to 38 inches above the tread nosings. The handrail must continue through the turn without interruption. Landings with an open side also need a guard at least 36 inches high with openings no larger than a 4-inch sphere.

Quarter-Turn Calculator

What Is the Quarter-Turn Calculator?

A quarter-turn stair changes direction by 90 degrees at a single turning point, making it the right choice when a straight flight will not fit your floor plan. Use this free quarter-turn stair calculator to split your total rise across two flights, size the landing or winder turn between them, and check that every riser, tread, and clearance meets residential code. Quarter-turn stairs go by several names: L-shaped stairs, 90-degree stairs, and single-turn stairs all describe the same layout. The turn itself can be built two ways. A flat landing platform gives you a comfortable place to pause, makes moving furniture around the corner much easier, and is the simpler option for most DIY builders. A winder turn uses pie-shaped treads to change direction without a landing, which saves floor space but is harder to build and less comfortable underfoot. Whichever option you choose, the math has to work as one system: both flights share the same total rise, so every riser in both flights must be exactly the same height. This calculator handles that split for you, computes the total run including the landing depth, and flags headroom problems at the turn where the upper flight passes over the lower one.

How to Use This Calculator

Enter the total rise, measured from the finished lower floor to the finished upper floor. Do not measure from the subfloor, because flooring thickness changes every riser.
Enter your target riser height. The IRC allows a maximum of 7-3/4 inches, but most builders aim for 7 to 7-1/2 inches for comfort.
Enter the tread depth (run). Residential code requires a minimum of 10 inches, measured nosing to nosing.
Choose your turn type: a flat landing platform or a winder turn. The calculator adjusts the layout math for each.
If you chose a landing, enter the stair width. The landing must be at least as wide and as deep as the stair itself, with 36 inches as the residential minimum.
If you chose winders, the calculator checks tread depth at the walkline, 12 inches from the narrow side, against the 10-inch minimum.

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