Stairs by floor height · 12 ft
Stairs for a 12 ft floor-to-floor height
12 ft (144″) from floor to floor takes 21 risers of 6 7/8″ and 20 treads 11″ deep: a pitch of 32°, and two risers and a going make 24 3/4″, an easy stride. A straight flight is 18′ 4 1/2″ long and needs an opening of 11′ 7 1/4″ in the floor above.
How it’s worked out
The fewest risers that keep each at most 18 cm (7″) high, all the same: 12′ ÷ 21 = 6 7/8″. The going follows the stair builders’ rule that two risers and a going make a stride of about 63 cm (25″). There is one tread fewer than risers: the last riser goes up to the upper floor itself.
If 12 ft is your ceiling height, the stair is taller: add the floor above it, usually 10–14″.
More or fewer steps
Fewer risers make a shorter, steeper stair; more make a longer, easier one.
| Risers | Each riser | Going | Pitch | Run of a straight flight | How it walks |
|---|---|---|---|---|---|
| 19 | 7 9/16″ | 9 13/16″ | 38° | 14′ 9 3/16″ | treads under the IRC’s 10″ |
| 20 | 7 3/16″ | 10 1/4″ | 35° | 16′ 2 1/2″ | comfortable |
| 21 | 6 7/8″ | 11″ | 32° | 18′ 4 1/2″ | comfortable (drawn here) |
| 22 | 6 9/16″ | 11 13/16″ | 29° | 20′ 8 1/16″ | comfortable |
The IRC (US homes) allows risers up to 7¾″ and asks for treads of at least 10″, 6′8″ of headroom and a width of 36″; states and towns amend it. Check the code that applies to yours.
This stair in each layout
Each drawn for 12 ft: the flights 36″ wide, the spiral 5 ft across, the square one in a 6 ft stairwell. The size is over the treads. Pick one for its plan, its sizes and its parts.
Change anything
A different width, a turn the other way, closed risers, a steel frame: open the stair in uCAD and set it in the panel, or tell the AI what the stair has to fit into.
Other heights
Other heights: 11 ft 9 in · all heights
Measured between finished floors. A few centimetres change the riser, not the count, until a riser passes 18 cm.