Stair parts made in Montana
Stair Stringer Calculator
Estimate the geometry of a straight cut stringer in inches. This layout aid reports stair counts, pitch and an estimated uncut throat; it does not size a structural member or approve a stair for construction.
Calculate a straight stringer layout
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Enter finished floor-to-floor rise, either total horizontal run or tread depth, and the actual board width measured across its face. Nominal lumber size is not its actual width.
Check your local code; requirements vary by jurisdiction.
Rise, run and stock width
Riser count uses the same 7.75 in planning maximum as our tread calculator. Divide total rise by riser count; the upper floor serves as the last tread, so tread count is one less.
Pitch comes from one repeated rise/run unit. The flight diagonal uses total floor-to-floor rise and total horizontal run; these are different reference lines when the top floor serves as the last tread.
Estimated throat is actual stock width minus the perpendicular depth of a repeated rise/run notch. It assumes the outer layout corners lie on the stock edge. Edge offsets, saw overcuts and end details reduce or change the usable section.
Before cutting or ordering
Diagonal length is not a finished board cut length. Top attachment, bottom bearing, tread thickness and any extra stock must be detailed separately.
Have a qualified builder or engineer check species, grade, thickness, span, spacing, loads, attachments and the remaining throat. No universal safe throat is established by this calculator.
Measure each finished step before requesting flooring-matched treads and risers.
Common questions
How do I calculate a stair stringer?
Find a consistent riser height and tread depth, then calculate the pitch and notch geometry. This calculator estimates the layout; a builder or engineer must check structural sizing and end connections.
Is stringer length the same as board length?
No. The reported flight diagonal is the hypotenuse of total rise and total run. Top and bottom details, layout offsets and extra stock determine the board length.
What is stringer throat?
The uncut depth remaining below the notches, measured perpendicular to the sloping stock edge. The estimate here assumes outer notch corners on that edge.
Which angle does the calculator show?
Pitch is the angle of one repeated rise/run unit above horizontal. Its complement is the angle to vertical. A saw setting depends on the cut and tool reference.
Does this calculator confirm code compliance?
No. It is a layout aid, not structural design or a code approval. Check your local code and have the complete stair reviewed before construction.
Ready for your stair parts?
Pricing and turnaround are confirmed on your written quote.