The build sequence a construction calculator follows
- Measure total rise (floor-to-floor, including finish allowances) and available total run (or the space you have to fit the stair into).
- Calculate riser count and exact riser height from total rise, checking against your local maximum riser height.
- Calculate tread going from available run and riser count, checking against your local minimum going and any pitch limit.
- Calculate stringer length from the pitch-line hypotenuse of total rise and total run, plus horizontal allowance at top and bottom.
- Work out tread and riser board sizes and quantities (see our treads and risers guide for the detailed take-off).
- Calculate handrail length, height and pitch (see our handrail guide).
- Calculate baluster or spindle count and spacing (see our baluster and spindle guides).
- Check headroom clearance through the full length of the flight against your local minimum.
Core dimensions at a glance
| Dimension | Typical formula | Confirm against |
|---|---|---|
| Riser count | Total rise ÷ target riser height, rounded | Local max riser height |
| Exact riser height | Total rise ÷ riser count | Local max riser height |
| Tread going | Available run ÷ (riser count − 1) | Local min going |
| Stringer length | √(total rise² + total run²) + end allowance | Physical fit and stock lengths |
| Pitch angle | arctan(total rise ÷ total run) | Local max pitch, if applicable |
| Headroom | Vertical clearance measured perpendicular to the pitch line | Local minimum headroom, commonly ≈2.0m / 6.5ft |
Headroom is the dimension people forget
It is entirely possible to satisfy every riser, going and pitch requirement and still fail on headroom, especially where a stair passes under an existing floor opening, beam or sloped ceiling. Check headroom along the whole flight, not just at the bottom, before committing to a design.
Worked example: a 2,850mm total rise flight
Total rise of 2,850mm divided by a target riser of roughly 180mm gives about 15.8, rounded to 16 risers. Exact riser height becomes 2,850 ÷ 16 ≈ 178mm. With 16 risers there are 15 treads; if available run is 3,750mm, going works out to 3,750 ÷ 15 = 250mm, which sits comfortably above a typical minimum going. Pitch angle is arctan(178 ÷ 250) ≈ 35.4 degrees. Stringer length is roughly √(2,850² + 3,750²) ≈ 4,710mm before end allowances — always confirm every figure against a physical site measurement before cutting material.
Materials checklist for a straight flight
| Component | Approx. quantity (15-tread example) | Notes |
|---|---|---|
| Stringers | 2 (or 3 with a centre carriage for wide stairs) | Length from pitch-line calculation plus allowance |
| Treads | 15 | Plus nosing overhang allowance |
| Risers | 16 (0 if open-riser) | Confirm riser style before ordering |
| Handrail | 1 length per side (or per code requirement) | See handrail length calculation |
| Balusters/spindles | 15-30 depending on spacing | See baluster calculation |
| Newel posts | 2-4 depending on turns/landings | At every direction change and flight end |
| Fixings | Structural screws, adhesive, brackets | Follow manufacturer/engineer specification |
Know your numbers in 30 seconds
Enter your step count, tread depth and riser height — the stair runner calculator gives you the exact length to order, in metres and feet, with waste included.
Open the stair runner calculatorWinders, landings and turns
The sequence above covers a single straight flight. Winders and half or quarter landings need each segment calculated and templated individually, because riser height should stay consistent through the turn even though tread shape and going change substantially at the turn. Get the straight-flight numbers locked in first, then treat the turn as its own mini-project with its own templates.
When to bring in an engineer or joiner
- Any stair carrying significant structural load beyond a standard domestic timber flight.
- Curved or helical stairs, which are essentially always templated and fabricated by a specialist.
- Stairs where headroom, rise or run is tightly constrained and a non-standard solution (space-saver, alternating tread) is being considered.
- Anywhere your calculated figures sit right at a code limit rather than comfortably inside it.
- Fire-rated or means-of-escape stairs in non-domestic buildings, which carry additional requirements beyond standard residential guidance.
Common full-build mistakes
- Sizing balusters or handrail before the exact tread width and pitch are confirmed from the core rise/run calculation.
- Forgetting to check headroom until the stringers are already cut.
- Using different riser heights for a winder section versus the straight flight either side of it.
- Ordering stringer stock to the bare calculated length with no allowance for housing joints or horizontal returns.
- Skipping a physical site re-measurement before cutting, relying only on drawn or assumed dimensions.
Whatever you decide, get the numbers first: the stair runner calculator doubles as a stair runner length calculator, adding nosing wrap, landings, winders, pattern repeat and waste so you order the right length the first time.
Frequently asked questions
What is the correct order to calculate a staircase build?
Total rise and run first, then riser count and height, then tread going, then stringer length, then tread/riser materials, then handrail, then balusters — each step depends on the one before it.
How do I calculate stringer length?
Take the hypotenuse of total rise and total run (√(rise² + run²)) to get the pitch-line length, then add an allowance at each end for housing joints or level returns.
What headroom clearance do stairs need?
A commonly cited residential minimum is around 2.0m (6.5ft), measured perpendicular to the pitch line along the whole flight, though you should confirm the figure that applies locally.
Do winders use the same riser height as the straight flight?
Yes, riser height should generally stay consistent through a winder section even though the tread shape and going change substantially at the turn.
How many stringers does a stair need?
Typically two, one at each side, though wider stairs sometimes add a centre carriage stringer for additional support — check span tables or an engineer's specification.
When should I hire a specialist instead of building from a calculator?
For curved or helical stairs, significant structural spans, tightly constrained headroom or rise/run, or any figure sitting right at a code limit rather than comfortably inside it.
What is a common mistake when calculating a full stair build?
Sizing handrail or balusters before the tread width and pitch are locked in from the core rise/run calculation, which often means redoing that work once the real numbers are confirmed.
Should I re-measure on site before cutting stringers?
Yes. Always confirm total rise and run with a physical site measurement immediately before cutting, since drawn dimensions can drift from as-built conditions.
Know your numbers in 30 seconds
Enter your step count, tread depth and riser height — the stair runner calculator gives you the exact length to order, in metres and feet, with waste included.
Run the full build calculationEvery guide is written from hands-on measuring and fitting experience, checked against the calculator’s own maths, and re-reviewed whenever prices or methods change. Read our editorial standards.