Calculate rise, run, number of steps, stringer length, and all materials needed. Checks IRC and IBC building code compliance automatically. Includes a visual stair diagram. Updated .
Check your stair dimensions against IRC (International Residential Code) and IBC (International Building Code) requirements. Use the Design tab to calculate dimensions first.
Complete material list for your stair project. Calculate from the Design tab first. Includes a 10% waste factor.
The sum of one riser plus one tread should equal 17-18 inches for a comfortable, safe staircase. A 7-inch riser with a 10-inch tread (sum: 17) feels natural to climb. A 7.5-inch riser with a 10.5-inch tread (sum: 18) also works well. Never exceed 7-3/4 inch rise or go below 10-inch tread per IRC code. Consistent riser height is critical, even a 3/8 inch variation can cause trips.
Building a staircase requires precise calculations to ensure safety, comfort, and code compliance. The relationship between rise (the vertical height of each step) and run (the horizontal depth of each tread) directly determines how comfortable and safe stairs are to climb. Stairs that are too steep feel tiring and dangerous; stairs that are too shallow waste space and feel awkward.
The classic ergonomic formula for comfortable stairs is: 2 × Rise + Run = 24"–25". For a 7" rise: 2 × 7 = 14, so run should be 10–11". For a 6.5" rise: run should be 11"–12". This formula, developed by 17th-century French architect François Blondel, has been validated by centuries of stair building and remains the gold standard for comfortable stair design.
| Dimension | IRC Minimum / Maximum | Recommended | Notes |
|---|---|---|---|
| Riser height | Max 7¾" (7.75") | 6¾"–7¼" | All risers must be within 3/8" of each other |
| Tread depth | Min 10" | 11"–11½" | Measured from nosing to nosing |
| Stair width | Min 36" | 36"–42" | Clear width between handrails |
| Headroom | Min 6'8" (80") | 7'0" | Measured vertically above stair nosing |
| Nosing projection | ¾"–1¼" | 1" | Overhang of tread beyond riser below |
| Landing depth | Min 36" | Equal to width | At top and bottom of stair |
| Handrail height | 34"–38" | 36" | Required if 4+ risers |
| Guardrail height | Min 36" | 42" | Required if open side 30"+ above floor |
Total rise is the vertical distance from the top surface of the lower floor to the top surface of the upper floor. For a deck, it's from the ground to the top of the decking. Measure this precisely, an error of even half an inch throws off all your riser heights. If your floor-to-floor measurement is, say, 108.5 inches, the calculator distributes that across the number of risers to give you even, code-compliant riser heights.
Stringer length = √(Total Rise² + Total Run²). This is the Pythagorean theorem applied to the hypotenuse of the right triangle formed by the stairs. A typical 9-foot ceiling stair with 11" treads: √(108² + 154²) = √(11664 + 23716) = √35380 ≈ 188" (about 15.7 feet). This is the minimum board length needed for each stringer, in practice you'll use a 16-foot 2×12.
Essential for consistent stringer layout, lock in your rise and run measurements
View on Amazon →Properly mounted handrail brackets are required by code for all staircases
View on Amazon →A circular saw is essential for cutting stair stringers accurately and cleanly
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