U-shaped stair calculator for iPhone.

A U-shaped or half-turn stair finishes in the opposite direction to the first flight. In this Pro² tool, you enter three flight lengths and three widths. Flights 1 and 3 are the parallel outer flights; flight 2 connects them between two 90° turns.

There is no separate gap input. In the illustrated arrangement, the clear plan distance between the parallel flights follows from L2 − W1 − W3. Do not treat flight 2’s full length as the gap.

Height H

Vertical finished floor-to-floor distance.

Flights 1 and 3

Enter the overall length and width of each outer flight. Their straight portions are L1 − W2 and L3 − W2.

Flight 2

Enter the full cross-flight length L2 and width W2. Its straight portion is L2 − W1 − W3 because both turn areas take space.

Turn settings

Choose two landings or winders, then the turn direction as you climb. Set the upper-floor connection separately.

Units

Lengths can use metric units or feet and inches; pitch is in degrees. The Balance value for winders is a percentage, not a dimension.

Choose Landings, a right turn and a top tread one rise below the upper floor. Enter H = 3060 mm; L1 = L3 = 2400 mm; L2 = 3400 mm; W1 = W2 = W3 = 1000 mm. Calculate and select 18 risers.

Each straight part is 1400 mm: 2400 − 1000 on the two outer flights, and 3400 − 1000 − 1000 on the middle flight. Five ordinary treads per flight give a 280 mm going.

The results give the total riser count and shared rise height, then a separate going and pitch for each flight. A change to one length or width can change the distribution across the whole stair. Do not assume all three goings remain equal in an asymmetric layout.

The example closes in both directions: each outer length is 5 × 280 + 1000 = 2400 mm, and the middle length is 1000 + 5 × 280 + 1000 = 3400 mm. The full height is (5 + 1 + 5 + 1 + 5 + 1) × 170 = 3060 mm.

The comfort card checks each flight’s geometry and 2 × rise + going. Its guidance is not building-code certification. The app does not turn the three flights into one straight-stringer length or a material cost.

The worked example is the landing mode only. It does not verify a winder arrangement with the same dimensions or count. A mode change needs its own check of the resulting plan and available straight goings.

Landings

Two separate flat turning surfaces. The first follows widths W1 and W2; the second follows W2 and W3. Their dimensions are derived from the flight widths, not a separate landing-depth field.

Winders

Winders spread each turn across shaped treads. Balance can extend the shaping into adjacent flight sections, so the number of non-rectangular treads is not fixed at three per turn. Check the plan and each tread detail. There is no separate winders-per-turn input.

Balance

The winder Balance control changes the turning contours and their relationship to adjacent straight sections. Review both turns and the individual tread details after adjusting it.

With Level with floor, the last numbered tread is at the upper-floor level. With One rise below, a separate final rise leads to the floor. That distinction changes how many numbered surfaces can be fitted into the same total riser count.

For the selected two-landing example: 18 = 15 ordinary treads + 2 landings + 1 final rise. The two landings have different elevations; the connecting flight climbs between them.

The app suggests a feasible riser count and supports manual adjustment. Supported counts are 8–40, but not every count fits every set of dimensions. A disabled control or no-solution message should be resolved by changing the layout, not by copying a neighbouring result.

The plan shows three connected flight regions, two turn areas and the route of ascent. Check that the outer flights have room between them and that each turn connects the intended widths. The elevation separates the two landing heights and the final upper-floor connection.

Tread details describe the surface contours with labelled vertices, side lengths and interior angles. For a winder, read the whole shape rather than interpreting one reported going as every edge length. Identical detail shapes can be grouped.

These are geometric drawings. Stock thickness, support conditions, joins, handrails and cutting allowances still need project-specific decisions.

• Dimensions must be positive and no greater than the supported 27,000 mm input limit. This is a software bound, not a building requirement.
• Both outer flights must leave length after the middle-flight width is reserved. The middle length must also accommodate both outer widths and a straight portion.
• A very small middle length can eliminate the gap or cause overlap; not every set of nominally valid dimensions creates a valid plan.
• The selected example is a three-flight, two-landing arrangement. It is not a separate two-flight tool with one broad intermediate landing.
• No cost, load capacity, headroom-envelope or regional-compliance calculation is included.

Why are there three flight fields?

This layout has two outer parallel flights and a connecting middle flight. Two 90° turns produce the overall 180° change of direction.

Where do I enter the gap?

There is no independent gap field. For the illustrated rectangular layout, the gap is L2 − W1 − W3: 1400 mm in this example.

Can I use the same dimensions for winders?

They are a starting set of measurements, not a verified winder solution. Changing turn type changes the surface allocation; inspect the recalculated plan and results.

Is the middle flight length measured along the sloping stringer?

No. Use the overall plan dimension L2 shown in the diagram. A sloping stringer length is a different measurement.