Stair Calculator
Lay out a code-compliant staircase with a live diagram.
Live Layout
15 risers · 14 treadsThese are example numbers. Tap any field below and enter your own measurements — every result updates instantly as you type.
Total Rise is required. Add a Total Run to lock the exact geometry — otherwise the targets below size the stairs.
Required — finished floor to finished floor.
Optional — leave blank to size the run from targets.
Guideline — sets how many risers the rise is divided into.
Guideline — used when no Total Run is given.
Finished tread stock — dropped from the bottom stringer cut.
Cut List
Code Check — 1 issue
Tools for this job
SponsoredGear we'd reach for on this job. As an Amazon Associate, BuildCalc earns from qualifying purchases — at no extra cost to you.
Coming in BuildCalcPro
Save jobs, export estimates as PDF, set custom local material prices. Vote on what to build first.
Join the waitlistCode checks reference IRC R311.7 residential limits. Always confirm against your local building code before cutting.
How the stair calculator works
BuildCalc's stair calculator turns one measurement — your total rise, floor to floor — into a complete cut list. It divides the rise into equal risers, derives the exact riser height and tread depth, and draws a live diagram you can check before cutting. Enter a total run to lock the geometry exactly, or leave it blank and let your target tread depth size the staircase.
Every layout is checked against IRC R311.7, the residential stair code: a maximum riser height of 7-3/4 inches and a minimum tread depth of 10 inches, plus comfort guidelines like the 2R + T rule. The cut list also includes the bottom riser cut — shortened by one tread thickness so the finished steps come out equal once treads are installed.
Guides
- How to calculate stair stringers (with IRC code rules) — math, code limits and a worked example for a 9 ft rise.
- How many stair stringers do I need? — spacing rules by tread material (wood, composite, metal) and stair width.
Stair calculator FAQ
How do I calculate stair stringers?+
Start with the total rise — finished floor to finished floor. Divide it by a target riser height (around 7 to 7-3/4 inches) and round to the nearest whole number for the riser count. The exact riser height is the total rise divided by that count. The tread count is one less than the riser count, and the stringer length is the diagonal: the square root of total rise squared plus total run squared.
What is the maximum riser height allowed by code?+
The International Residential Code (IRC R311.7.5) sets the maximum riser height for residential stairs at 7-3/4 inches. BuildCalc flags any layout that exceeds it.
What is the minimum stair tread depth?+
IRC requires a minimum tread depth of 10 inches, measured between the nosings. Deeper treads are more comfortable; the calculator warns you when a layout falls below the minimum.
What is the bottom riser cut, or stringer drop?+
Once treads are installed, each finished tread adds its own thickness on top of the step. To keep every finished step equal, the bottom of the stringer is cut shorter by one tread thickness. BuildCalc lists this bottom riser cut separately in the cut list.
What is a comfortable stair angle?+
Most comfortable stairs fall between 30 and 37 degrees. Steeper than about 37 degrees starts to feel like a ladder; shallower than 30 degrees uses a lot of floor space. BuildCalc reports the exact angle for your layout.
Do I need a total run to use the stair calculator?+
No. Total rise is the only required input. If you enter a total run, the calculator locks the geometry and divides it into exact treads. Leave it blank and your target tread depth sizes the run instead.