Measure Total Rise
Measure from the surface of the lower finished floor to the surface of the upper finished floor. This is the single most critical measurement — get it exact.
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A stair stringer calculator determines IRC-compliant riser height, tread depth, stringer length, and cut angles from your total rise measurement. It verifies dimensions against building code maximums and outputs fractional-inch measurements ready for marking on a framing square.
Stair Dimensions
Measure from finished floor to finished floor above
IRC min: 10" (excl. nosing)
Typical: ¾" – 1¼"
Stringer Results
Risers
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Riser Height
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Bottom Riser Cut
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Treads
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Tread Depth
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Stringer Length
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Plumb Cut
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Stair Angle
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Total Run
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Stringer Profile
Enter your total rise and hit Calculate to see the stringer profile.
How It Works
Auto-Calculate Risers
StairMaster divides total rise by an ideal 7" target to find the number of risers, adds one where that would push the riser past the 7¾" maximum, then calculates exact riser height to 1/16" precision.
IRC Code Check
Every dimension is checked against IRC R311.7: max 7¾" riser, min 10" tread, max ⅜" variance between risers. Red/green badges show compliance instantly.
Cut Your Stringers
The SVG diagram shows exact notch dimensions. Set your framing square to the riser and tread measurements, mark your 2×12, and cut. Then drop the stringer — take one tread thickness off the bottom seat, because a tread board lands on every notch but on neither floor.
Why Precise Stringer Layout Matters
Building code exists because uneven stairs cause falls. The International Residential Code (IRC R311.7) limits maximum riser height to 7¾ inches and requires minimum tread depth of 10 inches. More importantly, the maximum variance between the tallest and shortest riser in any flight is just ⅜ inch. Eyeballing it won't pass inspection. StairMaster calculates every dimension to 1/16" precision so every step feels identical underfoot. Enter your floor-to-floor height, and the calculator determines the number of risers, exact riser height, stringer length, and the plumb cut angle for your speed square — all verified against IRC code before you pick up a saw. It also gives you the bottom riser cut, which is not the same number: a tread board sits on every notch but on neither floor, so the stringer has to be dropped by one tread thickness or the first step ends up a full board proud of the rest and the top step the same amount short.
Frequently Asked Questions
What is the building code for stair riser height?
The International Residential Code (IRC R311.7) limits maximum riser height to 7¾ inches (196mm) and requires minimum tread depth of 10 inches (254mm). The maximum variation between any two risers in the same staircase is 3/8 inch. Local codes may be stricter — always verify with your building department.
How do you calculate the number of stair risers?
Divide the total rise (floor-to-floor height) by your target riser height (typically 7" to 7.5"). Round to the nearest whole number — that is your riser count. If that count leaves a riser taller than 7¾", add one more riser. Then divide the total rise by that count to get your exact riser height. Every riser must be identical within 3/8".
What angle should stair stringers be cut at?
Stair stringer angle depends on your specific rise/run ratio. Comfortable stairs typically fall between 30° and 37°. The cutting angle is calculated as arctan(riser height / tread depth). For a 7" riser and 10" tread, that is arctan(7/10) = 35°, which is considered ideal for residential stairs. That 35° is the pitch of the stair and the setting for your framing square; the plumb cut you mark across the board is its complement, 90° - 35° = 55°.
Why is the bottom stair riser cut shorter than the others?
Because a tread board lands on every notch in the stringer but on neither floor. Cut all the notches identically and the first step finishes one tread thickness taller than the rest while the top step finishes the same amount shorter — a 2 inch spread on 5/4 decking, against the IRC limit of 3/8 inch. The fix is to drop the stringer: cut the bottom seat down by exactly one tread thickness before you set it. After the drop, every finished riser is identical and the variance is zero.