CalcLibrary

Stair Calculator

Plan a straight staircase from total rise, target maximum rise per step, and tread depth. Get a practical layout with riser count, exact rise per step, tread count, total run, stringer length, and stair angle before you cut stringers or buy materials.

Units
m
cm
cm
Examples

A 2.85 m rise, 19 cm maximum rise, and 28 cm tread depth gives a long, comfortable run.

Recommended Riser Count
15
Exact Rise per Step
19 cm
Tread Count
14
Total Run
3.92 m
Stringer Length
4.85 m
Stair Angle
36 °

Top-landing assumption: 15 risers create 14 treads. Lowering the maximum rise usually adds risers; deeper treads increase run and usually flatten the angle.

Local building rules vary. Use this tool to plan a straight-stair layout, not to claim compliance, approval, or safety certification.

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Examples

How It Works

Formula

n=⌈Rhmax⁡⌉n = \left\lceil \frac{R}{h_{\max}} \right\rceil

h=Rnh = \frac{R}{n}

t=n−1t = n - 1

L=t⋅dL = t \cdot d

S=R2+L2S = \sqrt{R^2 + L^2}

θ=arctan⁡(RL)\theta = \arctan\left(\frac{R}{L}\right)

Variables

RR

Total rise between the two finished levels

hmax⁡h_{\max}

Maximum rise you will allow for one step

nn

Riser count, rounded up to a whole number

hh

Exact rise per step after the total rise is divided across all risers

tt

Tread count, assuming a top landing

dd

Depth of one tread

LL

Total run of the stair

SS

Stringer length in the side profile

θ\theta

Stair angle(°)

Enter total rise, the maximum rise you want per step, and tread depth. The calculator chooses the smallest whole riser count that keeps the exact rise per step at or below your limit. It then assumes a straight stair with a top landing, so tread count equals risers minus one. From there it computes total run, stringer length, and stair angle for the resulting layout.

Frequently Asked Questions

01Why is tread count one less than riser count?
This planner assumes a straight stair finishing at a top landing. You step onto the landing after the final riser, so the stair run has one fewer tread than risers.
02What happens if I lower the maximum rise per step?
The calculator adds risers until the exact rise per step falls at or below your limit. More risers usually means a gentler stair, but it also means more total steps to build.
03What happens if I make the treads deeper?
Deeper treads increase total run because each tread adds more horizontal distance. The stair usually becomes shallower, and the stringer gets longer.
04What does stringer length represent here?
It is the straight-line diagonal from the bottom of the stair to the top landing in this simple side profile. It helps you estimate the overall stringer geometry before detailed cut layout.
05How is this different from triangle math or material estimators?
Triangle calculators solve abstract side relationships, and material estimators count boards, sheets, or volume. This tool turns level-to-level rise plus stair assumptions into a practical straight-stair layout you can judge for fit.
06Does this confirm code compliance?
No. Local building rules vary by project and location. Use this calculator to plan geometry, then confirm your final stair design against the rules that apply where you are building.

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