Spiral Staircase Calculator — Rise, Going & Stringer Length
Design a spiral staircase by entering the floor-to-floor height, outer diameter, centre pole diameter, number of steps, and number of turns. Get rise per step, tread going at the walking line, rotation per step, and stringer (handrail) length.
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mm
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Rise within comfortable 150–220 mm range
- 1
Walking line radius
75 + ⅔ × 725 = 558.3Placed at two-thirds of the clear step width from the pole — where a foot naturally lands (BS 5395-2). - 2
Going at walking line
2π × 558.3 × 1 ÷ 13 = 269.9 - 3
Rise per step
2,700 ÷ 13 = 207.7
How does this calculator work?
rise = H/n. Going = 2π·R_walk·t/n, where R_walk = pole radius + ⅔ × step width. Stringer = √((2π·R_walk·t)² + H²). For H = 2700 mm, OD = 1600 mm, pole = 150 mm, 13 steps, 1 turn: rise ≈ 208 mm, going ≈ 261 mm, stringer ≈ 3048 mm. Aim for rise 150–220 mm and going 190–260 mm.
Formula
How this is calculated
A spiral staircase is a helix: each step rises by a fixed amount and rotates by a fixed angle around the central column. The rise per step equals the total floor-to-floor height H divided by the number of steps n. The "going" — the horizontal tread depth at the walking line — is the arc length of the walking line per step: going = 2π·R_walk·t / n, where t is the number of full turns and R_walk is the radius of the walking line. By convention the walking line is placed at two-thirds of the clear step width from the centre pole; this is where a person's foot naturally falls and where building standards (BS 5395-2, EN 14115) require the going to be measured.
The stringer is the helical element supporting the treads. At the walking-line radius, its total arc length is C = 2π·R_walk·t, and because it also rises H vertically, the stringer length is the helix hypotenuse √(C² + H²). The outer and inner stringers are longer and shorter respectively.
Comfort guidance (residential): rise 150–220 mm and going at the walking line 190–260 mm. Minimum clear step width between pole and balustrade is typically 600 mm for residential use. All inputs are in millimetres — to work in inches, substitute consistently and compare rise/going limits multiplied by 0.0394 (mm to in).
Frequently asked questions
The walking line is the arc where a person's foot naturally lands — placed at two-thirds of the step's clear width from the central pole. Building standards require that the tread going is measured at this line, not at the outer or inner edge.
One full turn (360°) is common for compact stairs connecting two floors. A 1.5- or 2-turn staircase gives a larger rotation per step or more steps for the same height, but needs more floor area for entry and exit.
IBC Section 1011.10 and EN 14115 allow spiral stairs serving occupied floors with an outer diameter as small as about 1200 mm (≈ 4 ft), though 1500–2000 mm is more comfortable. Always verify with your local building authority — requirements vary by jurisdiction and occupancy type.
Also known as
TG we-Calculate Editorial Team. (2026). Spiral Staircase Calculator — Rise, Going & Stringer Length [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/spiral-staircase-calculator
TG we-Calculate Editorial Team. "Spiral Staircase Calculator — Rise, Going & Stringer Length." TG we-Calculate. 2026. https://we-calculate.com/calculator/spiral-staircase-calculator.
TG we-Calculate Editorial Team, "Spiral Staircase Calculator — Rise, Going & Stringer Length," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/spiral-staircase-calculator
@misc{wecalculate_spiral_staircase_calculator, title = {Spiral Staircase Calculator — Rise, Going & Stringer Length}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/spiral-staircase-calculator}}, year = {2026}, note = {TG we-Calculate} }
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