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🪜 Stair Calculator

Calculate the number of risers, actual riser height, tread depth, stringer length, and total stair run. Checks compliance with IBC (7¾" max riser, 10" min tread) and generates a material list.

Floor-to-floor height

Typical: 6"–7¾"

Typical: 10"–11"

Stair Code Requirements

ParameterIBC (Commercial)IRC (Residential)
Max riser height7¾" (196 mm)7¾" (196 mm)
Min tread depth10" (254 mm)9" (229 mm)
Min headroom80" (2032 mm)80" (2032 mm)
Min stair width44" (1118 mm)36" (914 mm)
Riser + tread17–18.5"17–18.5"
'What is the stringer length formula?', 'answer' => 'Stringer length = √(total run² + total rise²) — the Pythagorean theorem applied to the stair triangle. Total run = number of treads × tread depth. Number of treads = number of risers − 1 (the top landing is not a tread).'], ['question' => 'What is the IBC riser-plus-tread rule?', 'answer' => 'The "comfort rule" states that riser height + tread depth should equal 17–18.5 inches. This balances the steepness and walking comfort of the stairs. For example: 7" riser + 11" tread = 18" (ideal). Another check: 2 × riser + tread ≈ 24–25" (the "2R+T" rule).'], ['question' => 'What lumber size is used for stair stringers?', 'answer' => '2×12 lumber is the standard stair stringer material in residential construction. It must be at least 3.5" of solid wood below the cut-out (net depth after notching). For long runs or heavy loads, engineered LVL stringers may be required. Tread boards are typically 5/4 × 12" deck board or 2×12 lumber.'], ]" />

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