Stair Stringer Calculator
Every riser equal, or it becomes a trip hazard.
Work out Stair Stringer. Every riser equal, or it becomes a trip hazard. Shows the working, not just the answer.
Set by your local building code
Stair geometry
14 risers at 185.7 mm
3,250 mm total run · 36.6° pitch
Every riser in a flight must be equal — an uneven one is a trip hazard because people climb stairs by rhythm rather than by looking. That is why the riser height is derived from the total rise divided by a whole number rather than set directly. The 2R + G rule at 621 mm sits in the comfortable range of roughly 550 to 700 mm. Note that there is always one fewer going than there are risers, because the top riser lands on the floor above.
How the Stair Stringer Calculator works
Stair geometry from a total rise: riser count, riser height, total run, stringer length and the 2R + G comfort check. Riser height is derived rather than set, because every riser in a flight must be identical.
Also known as: stair rise and run calculator · how many stairs for this height · staircase riser height calculator · stair stringer layout calculator
Why riser height is derived, never chosen
The total rise is fixed by the building — floor to floor. The riser count must be a whole number, so the riser height is the total rise divided by that count, and it will rarely be a round figure.
Setting the riser height directly and letting the last one make up the difference is the error this prevents. An uneven riser, particularly the top or bottom one, is a genuine trip hazard because people climb stairs by rhythm rather than by looking.
There is always one fewer going than there are risers, because the top riser lands on the floor above rather than on a tread. Counting them equal is the most common stair miscalculation and it makes the run one tread too long.
The 2R + G rule and what it encodes
Twice the riser plus the going should land somewhere around 550 to 700 mm. The rule encodes the relationship between step height and human stride: as steps get taller, the comfortable tread gets shorter, and the sum stays roughly constant.
A stair can meet code limits on riser and going individually and still fail this check, which is why it is worth calculating. Those stairs feel wrong to use — either cramped or oddly stretched — without an obvious reason.
Where the numbers do not work, adding a riser reduces each riser's height at the cost of a longer run. Where the run cannot grow, a winder or a landing is the answer rather than a steeper flight.
Headroom, layout and setting out
Headroom — typically 2 metres measured vertically from the pitch line — is the constraint that most often forces a stair layout to change. The pitch line joins the nosings rather than the tread surfaces, which is a common source of measurement error.
Winders turn a corner with tapered treads where a straight flight will not fit. Codes set minimum widths at the narrow end, because the inside of a winder is where people fall — the tread there is at its shortest exactly where the turn is tightest.
Setting out a stringer uses a framing square with stair gauges set to the rise and going, stepped down the timber. The bottom riser is reduced by the tread thickness so the finished risers come out equal — another place the arithmetic and the timber disagree.
Where to go next
The Stair Stringer question rarely arrives on its own. These are the ones that usually come with it:
- Joist Spacing Calculator — Depth beats width — stiffness goes with the cube.
- Rafter Length Calculator — The run is half the span less half the ridge.
- Board Feet Calculator — Board feet use nominal size, not the dressed size.
- Ring Size Calculator — Finger measurement to US, UK, EU and Japanese sizes.
Frequently asked questions
How do I calculate stair risers?
Divide the total rise by your preferred riser height and round to a whole number, then divide the total rise by that count. The result is the exact riser height, and it will rarely be a round number.
Why must every riser be the same?
Because people climb stairs by rhythm rather than by looking. An uneven riser — particularly the top or bottom one — is a genuine trip hazard and a code failure everywhere.
What is the 2R + G rule?
Twice the riser plus the going should land somewhere around 550 to 700 mm for a comfortable stair. It encodes the relationship between step height and stride length.
How many goings are there?
Always one fewer than the risers, because the top riser lands on the floor above rather than on a tread. Counting them equal is the most common stair miscalculation.
What are typical riser and tread limits?
They are set by local building code and differ between jurisdictions and between domestic and public stairs. Enter your own maximums rather than assuming — the difference between codes is substantial.
What if the stair does not fit the space?
Adding a riser reduces each riser's height at the cost of a longer run. Where the run cannot grow, the answer is a winder or a landing rather than a steeper flight.
What headroom does a staircase need?
Typically 2 metres measured vertically from the pitch line, set by local building code. It is the constraint that most often forces a stair layout to change.
How do I mark out a stringer?
With a framing square set to the rise and going using stair gauges, stepping down the timber. The bottom riser is reduced by the tread thickness so the finished risers come out equal.
What is a winder?
A tapered tread that turns a corner, used where a straight flight will not fit. Codes set minimum widths at the narrow end because the inside of a winder is where people fall.
How wide should a staircase be?
Domestic minimums vary by jurisdiction and are commonly around 800 to 900 mm. Wider feels considerably better and costs space in two rooms rather than one.
What is the pitch line?
The notional line joining the nosings, from which headroom and pitch are measured. It is not the surface of the treads, which is a common source of measurement error.
Are open risers allowed?
Frequently, with a limit on the gap so a small child cannot pass through — commonly 100 mm. Rules differ by jurisdiction and by whether the stair is domestic or public.
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Related calculators
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OpenBoard Feet Calculator
Board feet use nominal size, not the dressed size.
OpenRing Size Calculator
Finger measurement to US, UK, EU and Japanese sizes.
Open