What a 8-inch riser paired with a 9-inch tread actually gives you — pitch, comfort, and code status — plus the calculator to size a full flight.
An 8-inch riser with a 9-inch tread is non-compliant under IRC 2021 (max riser 7.75″, min tread 10.0″), and non-compliant under the IBC commercial standard (max riser 7.0″, min tread 11.0″).
This pair is one step's geometry. To size a complete flight for your floor-to-floor height, enter your total rise in the calculator and it will hold the riser near 8″ while checking every code limit.
An 8-inch riser with a 9-inch tread produces a 41.6-degree pitch, which is at the upper limit of buildable residential pitch for a staircase. In practice that means it is strictly space-saving and best reserved for secondary access. Its Blondel value of 25.0 inches lands right in the 24–25 inch Blondel comfort band, so it should feel natural underfoot.
Across a typical flight of about 14 treads, the 9-inch tread depth works out to roughly 9.8 feet of horizontal run — a compact footprint. Note that this pairing does not meet the residential IRC because the 8-inch riser exceeds the IRC's 7.75-inch maximum and the 9-inch tread is under the IRC's 10-inch minimum, so it would need adjustment before use in a typical home.
Reach for this pairing when floor space is tight and a steeper, more compact stair is acceptable — for example a secondary, basement, or loft stair rather than the primary staircase. Whatever your floor-to-floor height, the calculator below will hold the riser near 8 inches, divide the rise into uniform steps, and check the result against the code you select.