Calculate the perfect staircase dimensions. Enter total rise height and get the optimal number of steps, riser height, tread depth, stringer length and total going — with building code compliance checking.
Building Code GuidanceSVG Diagram
Staircase Dimensions
Number of Risers—
Actual Riser Height—
Number of Treads—
Tread Depth (going)—
Total Going (horizontal run)—
Stringer Length—
Stringer Angle—
2R + T Comfort Rule—
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Results are based on NCC/building code guidance (Australia). Local requirements may vary. Always consult a licensed builder or structural engineer before construction.
Standard Staircase Dimensions and Building Codes
Australian building code (NCC Volume One and Two) sets minimum and maximum dimensions for stair components to ensure safe, comfortable use:
Riser height: 115mm minimum, 190mm maximum for private stairs (residential). 115–180mm for public buildings.
Tread depth (going): 240mm minimum for private stairs, 250mm minimum for public stairs.
Stair width: 1000mm minimum for public stairs; 820mm common for residential.
Nosing: 15–25mm recommended. Rounded or bevelled nosing reduces trip hazard.
Handrails: Required on at least one side when there are 3 or more risers. Height 865–1000mm above nosing line.
International codes vary: IRC (USA) allows up to 220mm riser and 280mm minimum tread; UK Building Regs require 2R + T between 550–700mm for private stairs.
The 2R + T Rule Explained
The 2R + T formula is a centuries-old ergonomic rule from architect Francois Blondel (1675) that ensures stairs match the natural human walking stride. The formula states:
2 × Riser Height + Tread Depth = 550mm to 700mm
A result of 550–600mm feels steep; 630mm is generally considered ideal for most adults; 700mm feels shallow and can cause a shuffling gait. For example, a riser of 175mm and tread of 280mm gives 2×175 + 280 = 630mm — the sweet spot. This tool calculates the 2R+T value and flags any result outside the 550–700mm range as potentially non-compliant.
Frequently Asked Questions
The ideal riser height for residential stairs is 175mm–190mm. Australian building code (NCC) allows 115–190mm for private stairs and 115–180mm for public stairs. A riser of 175mm is the most comfortable for the average adult stride and is widely used as the design target. Risers above 190mm feel steep and tiring; risers below 150mm can cause people to trip or shuffle.
The minimum tread (going) depth for residential stairs in Australia is 240mm under NCC, though 280–300mm is recommended for comfort and ease of descent. Public stairs require a minimum of 250mm. Nosing overlaps of 15–25mm can extend the effective foot-landing area without increasing the total going of the staircase, making a shallower tread feel more spacious.
Stringer length is the diagonal measurement of the staircase frame, calculated using Pythagoras' theorem: Stringer = sqrt(totalRise² + totalGoing²). The total going equals the number of treads multiplied by the tread depth. For example, 16 risers of 175mm (total rise 2800mm) and 15 treads of 250mm (total going 3750mm) gives a stringer length of sqrt(2800² + 3750²) = approximately 4676mm or 4.68m. Add 150mm at each end for seat cuts.
The 2R + T rule states that twice the riser height plus the tread depth should equal between 550mm and 700mm for a comfortable staircase. This ergonomic formula dates from the 17th century and ensures stairs match the natural human stride length. A result of 630mm is widely considered optimal. For example: riser 175mm, tread 280mm → 2×175 + 280 = 630mm. Stairs outside this range may be technically code-compliant but will feel uncomfortable to use.