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Stair Rise and Run Calculator

Lay out a straight stair from total rise, target riser, available run, minimum tread, width, and landing length, then check geometry and plan area.

Floor-to-floor rise (mm)Target maximum riser (mm)Available horizontal run (mm)Entered minimum tread (mm)Stair clear width (mm)Entered landing length (mm)

Whole riser count-

Actual equal riser height (mm)-

Tread count for one straight flight-

Available run per tread (mm)-

Two risers plus one tread (mm)-

Actual tread minus entered minimum (mm)-

Overall stair angle-

Stair and entered landing plan area (m²)-

Decision view

Stair geometry and comfort-rule gauge

Stair geometry and comfort-rule gaugeA scaled flight labels total rise, available run, equal risers, tread depth, angle, and the two-riser-plus-tread comfort value.

Exact scenario comparisonTarget maximum riser (mm) changes while all other entered assumptions remain constant.

Target maximum riser (mm)	Whole riser count	Actual equal riser height (mm)	Tread count for one straight flight	Available run per tread (mm)	Two risers plus one tread (mm)	Actual tread minus entered minimum (mm)	Overall stair angle	Stair and entered landing plan area (m²)

How to use Stair Rise and Run Calculator

Enter total rise and a target maximum riser.
Enter the usable horizontal run and minimum tread.
Enter stair width and landing length.
Inspect the drawn staircase, dimension labels, and comfort gauge.

Calculator guide

Understanding Stair Rise and Run Calculator

A stair must divide total rise into equal whole risers while fitting its treads within the available run. This calculator exposes the integer rounding, actual riser and tread dimensions, comfort relationship, angle, and landing footprint.

Count first Whole risers control all subsequent geometry.

Equal heights Total rise is divided evenly.

One fewer tread A floor-to-floor flight ends at the upper floor.

Code still governs Geometry checks are not approval.

Calculation method

How the calculation works

Round riser count upward from total rise and target riser, distribute equal rise, then reconcile tread count, available run, comfort rule, angle, and plan area. Round the rise up to a whole riser count, divide total rise equally, use one fewer tread than risers, divide available run among treads, and calculate comfort and angle.

Detailed calculation process

Resolve whole risers before checking tread geometry

The defaults fit a 2,850 mm rise into 4,200 mm of horizontal run with a 180 mm target riser.

General formula: N_r = ceil(H/r_t); r = H/N_r; N_t = N_r-1; t = L/N_t; C = 2r+t; θ = atan(H/L); A_plan = (L+L_land)W/10^6 The ceiling creates enough equal risers to stay at or below the target height. A floor-to-floor straight flight has one fewer horizontal treads, so the available run is divided by that count.

What each symbol means

H / L Total vertical rise and available horizontal run, in mm.

r_t / r Target and actual equal riser height, in mm.

N_r / N_t Whole riser count and tread count, unitless.

t Actual tread depth, in mm.

C / θ Two-riser-plus-tread comfort value in mm and stair angle in degrees.

W / L_land / A_plan Stair width and landing length in mm, and plan area in m².

Worked substitution with the default inputs

1. Choose a whole riser count: N_r = ceil(2,850/180) = ceil(15.8333) = 16 risers Rounding up prevents the actual riser from exceeding the entered target.

2. Equalize riser height: r = 2,850/16 = 178.125 mm All modeled risers share the same height.

3. Fit the treads: N_t = 16-1 = 15; t = 4,200/15 = 280 mm The default tread exceeds the 250 mm minimum by 30 mm.

4. Check comfort and angle: C = 2×178.125 + 280 = 636.250 mm; θ = atan(2850/4200) = 34.1597° The comfort expression and geometric angle describe different aspects of the same flight.

5. Convert footprint to square metres: A_plan = (4,200+1,000)×1,000/1,000,000 = 5.200 m² One million square millimetres equals one square metre.

The default layout uses 16 equal 178.125 mm risers and 15 treads of 280 mm, with a 636.25 mm comfort value, 34.16° angle, and 5.20 m² plan footprint.

Stair geometry

Read every rise and run on the drawn flight

The engineering sketch scales the step pattern and adds a decision gauge for the comfort relationship.

Rise dimension Finished-floor vertical height.

Run dimension Horizontal flight extent.

Step module Equal actual riser and tread.

Comfort gauge The 2r+t value shown against a reference band.

Worked situations

Practical examples

2,850 mm divided by a 180 mm target requires 16 risers.
Fifteen treads across 4,200 mm are 280 mm each.
The default plan footprint is 5.20 m².

Better inputs

Useful tips

Measure finished-floor to finished-floor rise.
Check headroom, nosings, handrails, landings, and occupancy rules separately.
Use the actual rather than target riser in comfort checks.

Before relying on the result

Limitations and common mistakes

The model represents a straight idealized flight.
Winders, curved stairs, structural stringers, headroom, guards, and detailed code rules are excluded.
Local building and accessibility requirements govern final design.

Reference

Key terms

Riser: Vertical height between consecutive treads.
Tread: Horizontal going assigned to each step.
Comfort rule: A proportional check based on two risers plus one tread.

Important note

Calculated from the entered measurements and stated coverage or quantity rules. Confirm field dimensions, waste, product requirements, structural conditions, and local codes before purchasing or building.

Frequently asked questions

Why round the riser count up?

Rounding down would make each riser taller than the entered target.

Why are there fewer treads than risers?

The upper floor serves as the final walking surface in this straight-flight model.

Does a passing comfort value prove code compliance?

No. It is only one geometric rule of thumb.

Is the landing included in stair angle?

No. Angle uses the flight rise and available run only.