How to use
- Measure vertically from the lower finished floor to the upper finished floor.
- Enter the tread depth you want to test.
- Set your maximum riser and minimum tread using the requirements for your project.
- Calculate, then compare the total run with the space available for the flight.
How the estimate is calculated
Riser count is total rise divided by your maximum riser, rounded up. Dividing total rise by that count gives equal risers. The number of treads is one less than the riser count because the upper floor is the final surface. Run equals tread count × tread depth. The geometric diagonal is √(rise² + run²), and the angle is atan2(rise, run).
Example: a 108 in rise with a 10 in tread, a 7.75 in maximum riser, and a 10 in minimum tread gives 14 risers at 7.71 in each. There are 13 treads and 130.00 in of horizontal run. The diagonal is 169.01 in and the stair angle is 39.72°.
Inputs that control this layout
| Planning input | Starting value | Meaning |
|---|---|---|
| Maximum riser | 7.75 in | Editable limit used to choose the count |
| Minimum tread | 10 in | Editable comparison threshold |
| Tread depth | 10 in | Chosen depth that determines run |
| Upper floor | One final surface | Treads = risers − 1 in this model |
The initial riser and tread values are planning defaults with context in the Viewrail stair guide. Check your local building code; many US codes are based on the IRC. The table is not a statement that these limits apply to your location or stair type.
Measure finished surfaces and allow for connections
Floor finishes change the total rise. Include the planned lower and upper flooring before laying out equal risers. This tool assumes a single straight flight without a landing or winder and does not place a nosing.
The diagonal is a geometric reference, not the length of a stock stringer board to purchase or a cut pattern. Top and bottom attachments, bearing, notches, and trimming affect the board. Have those details checked together with headroom, width, guards, and handrails before construction.
Common mistakes
- Do not count the upper floor as another tread while also using this model’s full riser count.
- A result marked within your entered limits checks only those inputs; it cannot verify a complete stair.
- Do not round each riser independently and let the rounding error collect at one step. Keep the full layout consistent.
Sources
Default-value context: Viewrail tread-depth and riser summary, for background on the starting values. Flight geometry is calculated directly; no building-code section or local limit is asserted here.
Related calculators
- Board Foot Calculator — lumber volume after dimensions are specified
- Square Footage Calculator — measure surrounding floor space
Frequently asked questions
Can I change the maximum riser?
Yes. It is an input because your project requirements may differ. A lower maximum can increase the riser count and the resulting run.
Why is there one fewer tread than risers?
The model ends at the upper finished floor, which serves as the final walking surface. It counts only the treads below that floor.
Does the stringer length tell me what board to buy?
It is only the diagonal of the rise and run. Connection details, bearing, cuts, and trimming require additional consideration before choosing stock.
What if my tread is below my entered minimum?
The calculator still shows the geometry and warns that the tread fails your comparison. Revise the layout and confirm the applicable requirements.