Staircase Calculator
Enter floor height, target rise and going to compute the number of steps, actual rise, total run, stair angle and a Hong Kong residential compliance check.
Input Data
Results
At a glance:A stair flight is sized by step count = ⌈total height(mm) ÷ target rise⌉; actual rise = total height ÷ steps; total run = going × (steps − 1); stair angle = arctan(actual rise / going); 2R+G = 2×actual rise + going (a comfort measure). Hong Kong residential stairs commonly use rise ≤ 175 mm and going ≥ 250 mm; the tool flags compliance against this guideline. This is a preliminary check only and must follow the actual Building (Construction) Regulations.
Formula
Steps = ⌈height(mm) ÷ target rise⌉
Actual rise = height ÷ steps
Total run = going × (steps − 1)
Angle = atan(actual rise ÷ going)
2R+G = 2 × actual rise + going
Example: 3m, 170mm rise, 260mm going → 18 steps, 33.2°, 2R+G 600
$$n = \left\lceil \frac{H_{mm}}{R_t} \right\rceil$$$$R = \frac{H_{mm}}{n}$$$$Run = G(n-1)$$$$\theta = \arctan\!\left(\frac{R}{G}\right)$$$$2R+G = 2R + G$$How to Use
- Enter the total floor height (m).
- Enter the target rise per step (mm).
- Enter the going per step (mm).
- The tool outputs steps, actual rise, total run, angle, 2R+G and compliance.
Case Studies
Village house stair
Floor height 3 m, target rise 170 mm, going 260 mm.
18 steps; actual rise 166.7 mm; total run 4.42 m; angle 33.2°; 2R+G 593 mm.
Rise < 175 and going > 250, compliant with the residential guideline.
Steep stair adjustment
3 m, 200 mm rise, 220 mm going.
15 steps; 2R+G 620 mm but rise exceeds 175 → flagged non-compliant.
Lower the rise and widen the going to comply.
FAQ
Why steps − 1 for total run?
The run is the sum of the n−1 going gaps between n steps, not n×going; the top step meets the landing.
What does 2R+G mean?
A comfort measure: 2×rise + going (mm). Common comfortable range about 550–700 mm; too large or small feels awkward.
Is the compliance check legal?
It is a preliminary check against the common Hong Kong residential guideline (rise ≤ 175 mm, going ≥ 250 mm); actual design must follow the Building (Construction) Regulations and a professional survey.
Related Tools
References
Content review: Calculatorism Construction Team. Results are for reference only; please refer to the relevant authorities for the official figures.