Stair Geometry ToolStaircase Rise, Run & Pitch Calculator
Design a comfortable, code-compliant staircase. Calculate equal riser heights, going, pitch angle and the Blondel comfort check from your floor-to-floor rise, verified against UK, India, US or European standards.
Why this calculation matters
Rise and going decide whether the flight passes inspection and whether it is comfortable. Unequal risers are the most common cause of stair falls.
Stair Geometry Tool
Staircase Rise, Run & Pitch Calculator
Finished floor to finished floor.
Horizontal length available. 0 = auto from Blondel.
Comfortable ~175mm.
| Parameter | Value | Standard | Check |
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On the US preset. These are IRC (residential) limits: riser max 7¾″ (197 mm), tread min 10″ (254 mm). IRC requires a nosing of ¾″ to 1¼″ on solid-riser stairs where the tread is under 11″. Commercial work follows the IBC instead, which is stricter: riser max 7″ (178 mm) and tread min 11″ (279 mm). Check which code your job falls under.
About Stair Geometry Tool
A comfortable, safe staircase follows precise relationships between riser height and tread depth (going). Too steep and it is tiring and dangerous; too shallow and it wastes space. This tool divides your floor-to-floor rise into equal risers, calculates the matching going, and checks the result against the Blondel comfort formula and your chosen building standard - showing each check in a clear pass/fail table. Carpenters use it as a stair rise and run calculator on site, and the classic staircase formula comfort check flags awkward geometry before you cut a stringer.
Where Is This Used?
Formulas & Standards
Number of risers = round(Total rise / Target riser)Actual riser = Total rise / Number of risers (all equal)Number of treads = Risers - 1Blondel formula: 2 x Riser + Going = 550-700 mmPitch angle = arctan(Riser / Going), keep under ~42 degHow the calculation works
The rise is divided into equal steps first, because every riser in a flight must be the same — unequal risers are the most common cause of stair falls. Everything else follows from that. The Blondel figure checks the step against an average stride: comfortable flights land between 600 and 640 mm.
Show the formula
Number of risers = total rise / target riser, rounded. Actual riser = total rise / number of risers. Treads = risers - 1. Going = total run / treads. Blondel = 2 x riser + going. Pitch = arctan(riser / going).Checked against the selected rule set for maximum riser, minimum going, Blondel range 550-700 mm and maximum pitch. Straight flights only, landing level with the finished floor. Not a regulatory approval.
References and what each one provides
- IS 883Bureau of Indian StandardsIndian code of practice for design of structural timber, including permissible stresses, joint design and deflection limits.
Unverified values are marked as such rather than presented as sourced.
Limitations of this calculation
Checks geometry against the rule set selected. It is not a regulatory approval. It does not account for headroom, handrail and balustrade requirements, landing dimensions, fire escape provisions, or local amendments to the regulation.
Do not use this for Building regulation approval, fire escape design, or accessibility compliance sign-off.
Figures are engineering estimates from the inputs and assumptions shown. Verify against the actual material and, where the result affects structure or safety, against a qualified professional.
- Blondel’s rule (1675): 2R + G = 600–660 mm
- Pitch = arctan(R/G)
Formula checked against the sources above by an automated regression test (tests/verify-phase2.js) that derives each expected value independently of this page. Last reviewed .
How to use this tool
- Enter the job details below, then press Calculate.
- Pick your building standard from the dropdown.
- Fill in total rise, total run, target riser height.
- Press Calculate.
Worked example
Common mistakes to avoid
- Forgetting the finished floor thickness at top and bottom. The first and last riser end up unequal — a trip hazard and a code failure.
- Letting risers vary. Most codes allow only a few millimetres of difference between the tallest and shortest riser.
- Designing the going too short to save space. Comfort rule: 2×riser + going ≈ 600–640 mm.
Frequently Asked Questions
Wood species data
Density, hardness and movement for 60 timbers