Stair Calculator

A stair calculator helps compare stair layouts before detailed design. It estimates riser count, tread going, pitch, flight length, landings, floor opening, headroom, stringers, railing quantities and project cost for straight, quarter-turn and half-turn stairs.

A useful result depends on accurate finished dimensions and appropriate planning limits. Structural design, guarding, fire strategy and approval remain separate.

What the stair calculator can estimate

• the number of risers and treads;
• exact riser height and tread going;
• straight, quarter-turn and half-turn landing layouts;
• riser distribution between two flights;
• pitch angle and the 2R + G comfort relationship;
• horizontal run and stringer length for each flight;
• overall stair footprint in the available plan rectangle;
• landing and floor-opening area;
• simplified headroom and required opening length;
• alternative stair configurations;
• tread, riser-board and stringer material volume;
• handrail length, baluster count and preliminary cost.

Measure the finished floor-to-floor rise

The total rise is the vertical distance between the lower finished floor and the upper finished floor. It is not necessarily the same as the structural slab-to-slab distance.

Include tile, screed, timber flooring and underlay. A later change can make the first or last riser different.

Exact riser height = total finished rise ÷ number of risers.

Risers and treads are not the same count

A straight flight that reaches the upper floor normally has one fewer tread than risers because the upper floor acts as the final walking surface.

Treads in one flight = risers in that flight − 1.

A straight stair with 16 risers has 15 treads. Two flights split 8 + 8 have 7 + 7 treads, joined by the landing.

How automatic optimisation works

The automatic mode does more than round the total rise by a preferred riser height. It tests several riser counts and tread goings.

The calculator checks each candidate against:

• minimum and maximum riser height;
• minimum and maximum going;
• maximum pitch;
• the selected 2R + G range;
• minimum stair width;
• minimum headroom;
• maximum risers per flight;
• available plan length and width.

The calculator ranks candidates by passed checks and closeness to the preferred geometry. When none passes fully, it identifies the nearest option and failed checks.

Tread going and total run

The going is the horizontal distance from one nosing position to the next. It is different from the full board depth when the tread has a projection.

Flight run = number of treads × going.

Material estimates add the nosing to board depth, while geometry still uses the going.

Pitch angle

The stair pitch links the vertical rise and horizontal going:

Pitch = arctangent(riser ÷ going).

A 175 mm riser and 270 mm going produce a pitch close to 32.95 degrees. Reducing the going makes the stair steeper; increasing the going makes it longer.

Pitch alone is insufficient; tread relationship and headroom can still fail.

The 2R + G comfort relationship

A widely used step relationship is:

2R + G = 2 × riser height + going.

For a 175 mm riser and 270 mm going:

2 × 175 + 270 = 620 mm.

This relationship is a planning guide, not a universal rule. German workplace guidance recommends 59–65 cm and highlights 17 cm rise with 29 cm going.

Straight stair footprint

A straight stair is checked against the available rectangle in both orientations. The required plan dimensions are approximately:

length = total flight run;

width = clear stair width.

The calculator also tests a 90-degree rotation. Doors, walls and circulation still need separate clearance checks.

Quarter-turn stair with landing

A quarter-turn arrangement uses two flights meeting at a landing. The calculator distributes risers as evenly as possible and calculates each run separately.

Its simplified footprint uses:

overall length = first flight run + landing size;

overall width = second flight run + landing size.

The footprint model keeps the landing at least as deep as the stair width. Check door swings separately.

Half-turn stair with landing

A half-turn stair places two parallel flights beside each other. Its simplified plan dimensions are:

overall length = longest flight run + landing depth;

overall width = 2 × stair width + gap between flights.

This layout can fit a shorter rectangle. The gap may serve guarding, structure or finishes.

Landings and flight distribution

Two-flight stairs normally work best when the riser counts remain close. An odd total may produce one flight with one extra riser.

The calculator checks the maximum number of risers in each flight. It also estimates landing area for preliminary material costing.

Doors, escape direction and accessibility may require larger landings. Do not shrink one merely to force a fit.

Headroom and the floor opening

Headroom is one of the most important stair checks and one of the easiest to oversimplify.

The calculator uses the upper flight and estimates:

headroom = effective opening length × riser ÷ going − upper-floor thickness.

It also rearranges the relationship:

required opening length = (minimum headroom + floor thickness) × going ÷ riser.

This model does not replace a section drawing. Verify soffits, beams, finishes and the walking line.

Why alternative configurations matter

A small change in riser count can affect every other result. Fewer risers create taller steps and usually a shorter stair. More risers create lower steps but add treads and increase run.

The alternatives table lets a designer compare:

• riser count;
• exact rise and going;
• pitch and 2R + G;
• overall plan dimensions;
• number of passed checks.

The smallest footprint is not always best; comfort, headroom and structure may justify a larger stair.

England planning example

Approved Document K gives guidance for building work in England. For a private stair, its table includes risers from 150 to 220 mm, goings from 220 to 300 mm and a maximum pitch of 42 degrees. It also gives a 2R + G relationship from 550 to 700 mm.

Approved Documents allow other compliance routes, and a calculator profile does not guarantee approval.

France public-access example

French accessibility provisions for stairs normally open to the public set a minimum width of 1.20 m between handrails, a maximum step height of 16 cm and a minimum going of 28 cm. The same provisions also address contrasting nosings, tactile warning surfaces, lighting and handrails on both sides.

Other building categories use different requirements; a residential profile is not a public-access profile.

Germany workplace example

BAuA’s ASR A1.8 states that workplace stairs may use rises from 14 to 19 cm, goings from 26 to 32 cm and pitch angles from 24 to 36 degrees. The dimensions remain boundary values that must still be respected after permitted manufacturing and installation tolerances.

Public administration, schools, childcare and outdoor stairs use different ranges.

Sweden planning example

Boverket’s current safety guidance requires at least 2.00 m clear height in stairs and communication spaces. Its guidance also emphasises handrails, consistent geometry and safe movement.

Eligible projects may still use older BBR guidance until the end of June 2026; it recommends at least 0.25 m tread depth in or next to buildings.

Uniformity and finished dimensions

Keep every riser and going consistent. People develop a rhythm, so unexpected differences increase trip risk.

Before fabrication, confirm:

• lower and upper floor finishes;
• tread thickness and nosing;
• landing build-up;
• structural support levels;
• connections and tolerances.

Stringer length and preliminary materials

For each flight:

stringer length = square root of flight rise² + flight run².

The calculator multiplies this length by stringer count and waste. Tread and riser-board volumes are purchasing estimates, not structural design.

Handrails, guarding and balusters

The calculator estimates handrail length from flight stringer lengths and landing allowance. Baluster count follows the selected maximum spacing.

It does not determine guarding height, openings, handrail profile, posts or fixing strength.

Cost estimate

The calculator combines:

• tread-board volume;
• riser-board volume;
• stringer volume;
• landing area;
• handrail length;
• baluster count;
• labour per riser;
• other fixed project cost.

Estimated total = material items + railing items + labour + fixed cost.

Add stock lengths, fixings, finishing, transport, demolition and professional fees where relevant.

Practical workflow

1. Measure the finished floor-to-floor rise.
2. Measure available length, width and floor opening.
3. Select the intended stair layout.
4. Choose the correct regional and building-use limits.
5. Run automatic optimisation.
6. Compare the top alternatives.
7. Check headroom on a section drawing.
8. Confirm landings, handrails and guarding.
9. Have the structure designed and reviewed.
10. Update prices and material sizes before ordering.

Common mistakes

• measuring slab-to-slab instead of finished floor levels;
• using the same count for risers and treads;
• including nosing in the going;
• checking pitch but not 2R + G;
• ignoring floor thickness in headroom;
• forcing a landing below the stair width;
• forgetting to check the rotated footprint;
• treating regional example limits as approval;
• using material volume as structural sizing;
• fabricating before final floor finishes are known.

Frequently asked questions

Official sources

• UK Government: Approved Document K
• Légifrance: accessibility provisions for public stairs
• BAuA: ASR A1.8 Verkehrswege
• BAuA: designing safe stairs
• Boverket: safe stairs and ramps
• Boverket: stair guidance under older BBR rules

Sources reviewed: 22 June 2026.