Stair Stringer Calculator — Rise, Run & Layout
Stair geometry diagram
Measure between finished floor levels. Inches accept decimals or fractions such as 7 3/4; millimetres accept decimals. A decimal comma is also accepted. Do not group thousands.
Editable stair examples
Optional: check vertical headroom below a horizontal upper floor. Measure the finished opening, not the framing rough opening.
2. Your stair geometry
- Riser height meets your 7 in preference.
- Going meets your 10 in preference.
- No available-run limit entered.
These checks compare your own dimensional preferences. They do not certify building-code compliance or structural capacity.
Floor opening and headroom
Drag to see the finished header move. The opening field also accepts lengths beyond the flight.
A horizontal ceiling across the full stair width is assumed. Beams, sloped ceilings, approach geometry and the upper landing need separate checks. This is a finished opening estimate, not a framing cut size or building approval.
Compare nearby riser counts
Choose a card to use that count. More risers reduce the rise per step; the run or going changes with your selected mode.
Understand the stringer length estimates
- One rise/run diagonal (unit of bridge)
- 12.207 in
- Layout length estimate: risers × unit of bridge
- 183.098 in
- Floor-to-floor envelope diagonal
- 175 in
- Geometric tread depth: going + nosing
- 11 in
- 2 × riser + going
- 24 in
The layout estimate is a planning allowance, not a finished cut length or a guaranteed stock minimum. Top and bottom connections, end cuts, tread thickness and the selected construction method affect the actual stringer. Do not cut lumber from the overall diagonal alone.
Why are there fewer treads than risers?
Why are there fewer treads than risers?
For one straight flight between finished floors, the upper floor supplies the final landing. With 15 equal rises there are 14 separate treads. The model excludes intermediate landings, winders, spirals and a separate top tread at the same level as the floor.
Rise, going and nosing
Rise, going and nosing
Riser height is total rise divided by the riser count. Going is the horizontal step spacing. Nosing projects beyond the riser below, so this planner adds it to geometric tread depth while keeping the going and floor run unchanged.
How the calculation works
How the calculation works
Automatic risers = ceiling(total rise ÷ preferred maximum), with at least two risers. Total run = (risers − 1) × going. Step pitch = atan(riser height ÷ going). In fit-to-space mode, going = available run ÷ (risers − 1). Display rounding does not change the calculated equal risers.
What is the stringer estimate?
What is the stringer estimate?
The unit of bridge is √(riser² + going²). Its product with the riser count is one way to estimate layout length. The overall diagonal √(total rise² + total run²) connects different endpoints and is shown separately. The BC Carpenter stair-systems training guide, printed pages 26 and 44, explains these estimating methods. Its local code dimensions are not applied here as US rules.
How much floor opening is needed?
How much floor opening is needed?
The optional indoor check measures headroom vertically from the line connecting the tread nosings. Required finished opening = (floor assembly thickness + clearance target) × going ÷ equal riser height. Use the slope of one step, not the floor-to-floor envelope diagonal. Clearance at the finished header = opening × equal riser height ÷ going − floor assembly thickness.
The opening is measured from the upper landing nosing. When its lower edge is beyond the first tread nosing, this flight-only model cannot give a header clearance. The full required length remains visible; approach and landing geometry need their own checks. The BC Carpenter Level 1 training guide, printed pages 30–32, explains the similar triangles and finished versus rough openings. Its local code targets and framing allowance are not applied as US rules.
Before construction
This is a geometry planner for one straight flight, up to 60 risers, 15 m total rise and 30 m total run. Verify local requirements and a suitable structural design, including supports and connections. The illustrated preferences are editable examples, not an approval to build.
Continue the project
Continue the project
For the landing surface, use the deck board layout calculator. For a separately measured straight railing bay, use the baluster spacing planner to check clear gaps after rounding tape marks. When quoting lumber, use the board-foot purchase tally. For a separately designed concrete landing, estimate material with the concrete calculator.
Plan a straight staircase, fit the available space and compare riser counts. See a proportional drawing and print your dimensions in inches or millimetres.
