Stair Calculator
Risers, treads, total run and headroom — checked against the reference you pick.
Straight flight
= 108" (9')
= 7 1/2"
= 10"
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Stairs · Result
CalculatedRISER HEIGHT
riser height 7 11/16"
- Risers
- 14
- Treads
- 13
- Total run
- 10' 10"
- Angle
- 37.6°
2021 IRC reference check — within the limits checked. Local requirements may differ.
Reference profile 2021 IRCA reference check is not a compliance determination; local amendments differ.
SettingChangeLimits come from the 2021 International Residential Code reference profile — R311.7.1, R311.7.2, R311.7.3, R311.7.5.1, R311.7.5.2 (screenshots 01–03). This is the standard checked against, not a determination of the code governing this project: A reference check against the 2021 IRC, not a determination of the code governing this project: adoption, local amendments, occupancy and building type are not modelled.
SUGGESTED DEFAULTCode references & assumptions · 2
How this result is supported
- SUGGESTED DEFAULTLimits come from the 2021 International Residential Code reference profile — R311.7.1, R311.7.2, R311.7.3, R311.7.5.1, R311.7.5.2 (screenshots 01–03). This is the standard checked against, not a determination of the code governing this project: A reference check against the 2021 IRC, not a determination of the code governing this project: adoption, local amendments, occupancy and building type are not modelled.
- ASSUMPTION
- ASSUMPTIONA flight of n risers has n − 1 treads; the top floor is not a tread
- CONVENTION
What do these evidence labels mean?
- PRIMARY-VERIFIED
- directly supported by one authoritative primary source, quoted with section/page/figure
- CROSS-VERIFIED
- independently supported by two or more appropriate authoritative sources
- DERIVED
- mathematically derived from PRIMARY-VERIFIED values; the derivation is preserved in data and in code
- INTERPRETED
- a source exists but translating it into calculator behaviour required interpretation
- CONVENTION
- recognised trade practice, not a mandatory provision
- ASSUMPTION
- product/design assumption or useful default with no authoritative basis
- UNVERIFIED
- insufficient authoritative evidence
Code references and product data are quoted in the units their source uses.
Reference checks are informational, not compliance determinations.
How stair is calculated
This calculates STRAIGHT flights — one run from floor to floor with no turn in it. Winders, landings and switchbacks change both the geometry and the code provisions that apply, and a number from this page should not be carried onto them.
The total rise is divided evenly by the riser count, because risers in a flight must be equal — an uneven one is the classic trip hazard and every reference limits how much they may vary. The tread count is one less than the riser count, since the upper floor itself is the last tread.
Alternatives either side of your riser count are shown because the choice is usually a trade-off rather than a calculation: one more riser makes each one shorter and the flight longer, and which you want depends on the space you have.
The reference check reports what the selected document says about riser height and tread depth. It names the document it read; it does not tell you whether your stair may be built, and local amendments differ.
riser height = total rise ÷ riser count
tread count = riser count − 1
The top landing is the last tread.
total run = tread count × tread depth