SettingsSettings for this calculationUS
The measured vertical clearance above the spiral stair treads/nosings.
Measure the minimum vertical clearance from the leading edge (nosing) of any tread to the underside of any overhead obstruction (framing, ceiling, or the stair's own structure above) along the full walking line of the stair.
Actual headroom clearance
6.5 ft
The clear headroom is at or above the 78 in (1.9812 m) in IBC Section 1011.3's spiral-stairway exception. That reduced clearance is available only where the stair also meets Section 1011.10's other spiral provisions — tread depth, riser height and diameter — none of which are checked here, and local amendments vary. Matching the figures quoted is not compliance. The rest of the requirement, and the installed work, are outside what this page can see.
- Required minimum (IBC 1011.3, spiral stair exception)
- 6.5 ft
They open the calculator with your figures already in it
Spiral Stair Headroom Clearance Calculator: 6.5 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Show calculation logicHide calculation logic
How this was calculated
Formula source(s)
- Per the International Building Code Section 1011.3 (verified against a regulatory-text mirror this session, up.codes): standard stairways require 80 inches (2032mm) minimum headroom, but 'Spiral stairways that comply with Section 1011.10 are permitted a reduced headroom clearance of 78 inches (1981mm / 1.9812m).'
Inputs used
- Actual Measured Headroom Clearance
- 6.5 ft
Intermediate steps
- Required minimum (IBC 1011.3, spiral stair exception)
- 6.5 ft
Confidence note: The clear headroom is at or above the 78 in (1.9812 m) in IBC Section 1011.3's spiral-stairway exception. That reduced clearance is available only where the stair also meets Section 1011.10's other spiral provisions — tread depth, riser height and diameter — none of which are checked here, and local amendments vary. Matching the figures quoted is not compliance. The rest of the requirement, and the installed work, are outside what this page can see.
What this calculation does not cover
- Compares against whatever is there on the day. The requirement is to the FINISHED surface, so a plastered soffit, a trim ring round the floor opening, a pendant light hung in the well or a thicker floor build-up all come off the figure after the framing has passed. The whole margin between the standard 80 in and this 78 in exception is 51 mm — about two inches of finish.
- 78 in is US model code and travels no further. In England the governing figure is Approved Document K: 2.0 m over a stair generally, relaxing to 1.9 m at the centre of the stair width only for a loft conversion, and with no spiral exception at all. A stair that satisfies IBC 1011.3 can still be short where that code applies.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Per the International Building Code Section 1011.3 (verified against a regulatory-text mirror this session, up.codes): standard stairways require 80 inches (2032mm) minimum headroom, but 'Spiral stairways that comply with Section 1011.10 are permitted a reduced headroom clearance of 78 inches (1981mm / 1.9812m).'
Which documents these citations point at
- International Building Code — Section 1011.3 (United States)Buildings other than the dwellings the IRC covers — occupancy, egress, fire resistance and structural provisions.
A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.
Cite this page
Your workspace
Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.