Stair Calculator for Safe, Code-Compliant Steps
This stair calculator turns a floor-to-floor height into the exact dimensions you need to build a comfortable, code-compliant staircase. Enter the total rise and a riser height (or step count) and it works out the number of steps, actual riser height, tread depth, stair angle, and stringer length in seconds.
It is built for builders, deck contractors, architects, and DIY remodelers who want measurements that actually pass inspection. Every result is checked against standard building-code limits, scored with the comfort rule (2R + T), and drawn as a side-view diagram so you can see the staircase before you cut a single board.
How to Use the Staircase Calculator
Choose a calculation mode
Pick By Total Rise if you only know the vertical height, or By Rise + Run if you know both the vertical and horizontal distances.
Select your unit system
Switch between mm (metric) and in (imperial). Existing values convert automatically when you toggle units.
Enter the total rise and rise method
Type the floor-to-floor height, then choose Fixed Riser Height or Fixed Number of Steps. The riser height is then adjusted so every step is exactly equal.
Add tread depth and optional details
In By Total Rise mode, enter the tread depth (in By Rise + Run it is computed for you). Add Nosing and Stair Width for material estimation, or open Headroom Check to enter the floor opening and floor thickness.
Read your results
Review the results grid, compliance checks, comfort-rule badge, material estimate, and stringer notch detail. The SVG diagram updates live as you type.
Features
Two Calculation Modes
Use By Total Rise when you set the tread depth yourself, or By Rise + Run to compute tread depth from the horizontal distance.
Fixed Riser or Fixed Steps
Specify a preferred riser height and get the step count, or set the number of steps and get the riser height. Either way, all steps come out exactly equal.
Metric and Imperial Units
Switch between millimeters and inches with one click. Inputs convert automatically and all results display in the selected unit.
Real-Time Calculation
Results, compliance checks, and the diagram update instantly as you type — no calculate button to press.
Building Code Compliance
Each dimension is checked against standard limits — riser 100–196 mm, tread ≥ 254 mm, nosing 19–32 mm, angle 30°–37°, width ≥ 914 mm, headroom ≥ 2,032 mm — with a pass or warning badge.
Comfort Rule (2R + T)
The 2R + T formula is rated Optimal (600–650 mm), Acceptable (550–700 mm), or Poor with a color-coded badge so you know how the stairs will feel underfoot.
Headroom Clearance Check
Enter the floor opening length and floor thickness to verify clearance against the 2,032 mm (6' 8") minimum.
Material Surface Area
Add the stair width to estimate tread and riser surface areas separately, plus the combined total, in m² or ft².
Stringer Notch Detail
Get the plumb cut, level cut, notch depth, and minimum board width (notch depth plus 89 mm of remaining wood) for cutting your stringers.
Interactive SVG Diagram
A scaled side-view drawing shows rise, run, riser height, tread depth, nosing, stringer length, and angle, displaying up to 20 steps for clarity.
Building Code Reference Table
A built-in table lists the standard requirement for each stair parameter so you can compare your design against code at a glance.
Frequently Asked Questions
How do I calculate the number of steps?
Divide the total rise by a comfortable riser height (around 175–180 mm / 7"), then round up to the nearest whole number — that is your number of risers. The calculator does this for you in Fixed Riser Height mode and then evens out the riser height so all steps match. The number of treads is one less than the number of risers.
What is the standard stair rise and run?
Most building codes keep the riser (rise) between 100 mm and 196 mm (about 4"–7.75") and require a tread (run) of at least 254 mm (10"). A riser near 175–180 mm (7") paired with a tread of 254–280 mm is widely considered the most comfortable combination for residential stairs.
What is the 7-11 rule for stairs?
The 7-11 rule is a common rule of thumb: a riser of about 7 inches with a tread of about 11 inches gives stairs that feel natural to climb. It lines up closely with the comfort rule (2R + T): 2 × 7" + 11" = 25", which falls right inside the optimal 600–650 mm band this calculator uses.
What is the comfort rule (2R + T)?
The comfort rule takes twice the riser height plus the tread depth. A result between 600 and 650 mm (about 24"–25.5") indicates stairs that feel natural to walk on. The calculator rates your design as Optimal (600–650 mm), Acceptable (550–700 mm), or Poor outside those ranges.
How do I measure a stair stringer length?
The stringer is the diagonal board that supports the steps. Its length is the hypotenuse of the total rise and total run — the square root of (rise² + run²). This calculator works it out automatically and also gives the stringer notch detail: plumb cut, level cut, notch depth, and the minimum board width needed to leave at least 89 mm (3.5") of wood behind each notch.
What is a comfortable stair angle?
The stair angle is the incline measured from horizontal. Comfortable residential stairs usually fall between 30° and 37°. Steeper angles are harder to climb, while shallower ones need more floor space. The compliance check flags an angle outside this range with a warning.
What is nosing and is it required?
Nosing is the part of the tread that overhangs the riser below, adding walking surface without increasing the total run. Codes typically allow 19 mm to 32 mm (0.75"–1.25"). Nosing is optional here — leave it blank and the calculation simply proceeds without it.
How is headroom calculated?
Headroom is the vertical clearance between the stair surface and the structure above. Open the Headroom Check section and enter the floor opening length and floor thickness; the calculator derives the clearance from those plus the rise and run and compares it to the 2,032 mm (6' 8") minimum.
Is my data stored or shared?
No. All calculations happen entirely in your browser. Your measurements and results are never sent to any server or saved anywhere.
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