Awaiting expert review. This page covers safety or regulatory rules that change over time. It is kept out of search results until a qualified reviewer has checked it; the sources below are dated so you can verify each point.
Quick answer
Stair rise and run are the two dimensions of each step: the rise, or riser height, is the vertical distance from one tread nosing to the next, and the run, or tread depth, is the horizontal distance between those nosings, measured at a right angle to the tread edge.
For houses, the 2021 IRC allows a riser of up to 7-3/4 inches and a tread of at least 10 inches, and every step in a flight must match within 3/8 inch.
Quick facts
The key facts about Stair Rise and Run, with sources:
- Maximum riser (IRC)
- 7-3/4 inches, 2021 IRC R311.7.5.1 1
- Minimum tread (IRC)
- 10 inches, 2021 IRC R311.7.5.2 1
- Allowed variation
- 3/8 inch between largest and smallest in a flight 1
- Nosing
- 3/4 to 1-1/4 inches, unless the tread is at least 11 inches 1
- Headroom
- 6 feet 8 inches minimum 1
- Commercial comparison (IBC)
- 7-inch max riser, 11-inch min tread 2
- Stair injuries
- About 1.08 million U.S. emergency visits a year, 1990–2012 4
Key takeaways
- Rise is the step height; run is the step depth, both measured nosing to nosing.
- Houses under the 2021 IRC: riser no more than 7-3/4 inches, tread no less than 10 inches.
- Uniformity matters as much as size: risers and treads in one flight may differ by no more than 3/8 inch.
- Laying out a stair starts from the total floor-to-floor height, divided into equal risers.
- Rebuilding an existing stair may keep its old geometry only where the space truly does not allow a gentler slope, under the IEBC.
Rise and run in plain terms
A stair is a series of small vertical lifts and horizontal steps. Each lift is a rise; each step forward is a run.
Builders also talk about the total rise, the full height from one finished floor to the next, and the total run, the full horizontal length the stair takes up.
The 2021 International Residential Code (IRC) measures riser height vertically between the leading edges of adjacent treads, and tread depth horizontally between the foremost projections of adjacent treads, at a right angle to the tread’s leading edge 1. It also says carpets, rugs and runners are not counted in those dimensions 1.
Rise and run together set the stair’s steepness. A tall rise with a short run makes a steep, ladder-like stair. A low rise with a deep run makes a gentle stair that needs more floor space.
- Riser heightVertical, nosing to nosing; 7-3/4 in. max (IRC)
- Tread depthHorizontal, nosing to nosing; 10 in. min (IRC)
- NosingFront edge overhang; 3/4 to 1-1/4 in.
- StringerThe sloped board that carries the treads
- Handrail34 to 38 in. above the nosing line
- Headroom6 ft 8 in. above the nosing line
Dimensions from 2021 IRC Section R311.7. They are model code values; your jurisdiction may amend them. Source: [1]
How a stair is laid out from rise and run
A stair designer works from the total rise down to each step. The order matters, because every step must come out equal.
- Measure the total rise from finished floor to finished floor, including flooring that is not yet installed.
- Divide by the maximum riser. Total rise ÷ 7.75 inches gives the fewest risers allowed; round up to a whole number 1.
- Find the actual riser. Total rise ÷ that number of risers gives the equal riser height.
- Count treads. A straight flight has one fewer tread than risers, because the top floor is the last step.
- Set the run. Choose a tread depth of at least 10 inches; multiply by the tread count for the total run 1.
- Check the rest. Confirm headroom of 6 feet 8 inches, landings at top and bottom, and a flight rise no more than 12 feet 7 inches between landings 1.
Designers often round the riser count up by one more to get a gentler stair, if the floor space allows the longer run.
Rise and run rules by stair type (2021 IRC)
| Stair type | Max riser | Min tread | Other key limits |
|---|---|---|---|
| Standard straight stair | 7-3/4 in. 1 | 10 in. 1 | 36 in. clear width; 3/8 in. max variation |
| Winder treads | 7-3/4 in. 1 | 10 in. at the walkline; 6 in. at any point 1 | Walkline 12 in. from the inside of the turn |
| Spiral stair | 9-1/2 in. 1 | 6-3/4 in. at the walkline 1 | 26 in. clear width; 6 ft 6 in. headroom |
| Alternating tread device | 9-1/2 in. 1 | 5 in. tread; 8-1/2 in. projected 1 | Not a means of egress except small lofts |
| Ship’s ladder | 9-1/2 in. 1 | 5 in.; 8-1/2 in. with nosing 1 | Not a means of egress except small lofts |
| Commercial stair (IBC, for comparison) | 7 in. max, 4 in. min 2 | 11 in. 2 | Applies to buildings under the IBC |
Example: laying out a basement stair for a 108-inch floor-to-floor height
A worked layout using the 2021 IRC limits 1. The total rise is an example value; always measure finished floor to finished floor.
| Step | Figure | How it was worked out |
|---|---|---|
| Total rise | 108 in. | Example: basement slab to finished first floor |
| Fewest risers allowed | 108 ÷ 7.75 = 13.9, round up to 14 | IRC max riser 7-3/4 in. |
| Actual riser height | 108 ÷ 14 = about 7-23/32 in. (7.71 in.) | Under the 7-3/4 in. limit |
| Number of treads | 14 − 1 = 13 | Top floor is the last step |
| Total run at 10 in. treads | 13 × 10 = 130 in. (10 ft 10 in.) | IRC min tread 10 in. |
| Gentler option: 15 risers | 108 ÷ 15 = 7.2 in. riser; 14 treads × 10.5 in. = 147 in. | More comfortable, needs about 17 in. more floor |
| Landings | At least 36 in. deep at top and bottom of a straight run | IRC R311.7.6 |
Riser height = Total rise ÷ Number of risers (where Number of risers = Total rise ÷ 7.75, rounded up)
Total rise- Finished floor to finished floor, in inches
7.75- IRC maximum riser height in inches
Total run- (Number of risers − 1) × tread depth
Every riser and tread in a flight must then fall within 3/8 inch of the others.
Source: [1]
The math shows why stair space is hard to find in remodels. A code-minimum basement stair here needs nearly 11 feet of run plus landings, and a more comfortable one needs over 12 feet.
Where rise and run come up in a remodel
Basement finishing. Old basement stairs are often steep and uneven. A basement finish that makes the space habitable is when inspectors and owners look hardest at the stair.
Additions and attic conversions. A new addition or attic room needs a code stair, and its footprint often decides the floor plan.
Flooring changes. Adding thick tile or a new subfloor at the top or bottom changes the first or last riser. A 3/4-inch change can push a flight past the 3/8-inch variation limit 1.
Inspection. Inspectors measure risers and treads at framing and final. Our guide to permits and approvals explains when those inspections happen.
Plan for the finished floors
Measure total rise from finished floor to finished floor. If a hardwood floor will go on the upper level and tile on the lower, add and subtract those thicknesses before you cut stringers, or the top and bottom steps will not match.
Why correct rise and run matter
Getting it right
- Steps the body can predict, which reduces trips and missteps.
- A stair that passes inspection on the first visit.
- Room for handrails, nosings and headroom that work together 1.
- Easier use for children, older adults and people carrying loads.
What the rise-and-run rule does not cover
Rise and run set geometry. They do not set slip resistance, lighting, handrail grip or guard height, each of which has its own rule. The IRC handles lighting in R303.7 and R303.8, handrails in R311.7.8 and guards in R312 1.
They are also minimums for safety, not comfort targets. A stair built to the 7-3/4 inch and 10 inch limits is steeper than the 7 inch and 11 inch stair the International Building Code (IBC) requires in most other buildings 2. Many designers aim between the two in homes where space allows.
Finally, the IRC exempts some stairs: those not serving a building, porch or deck, and those leading only to nonhabitable attics or crawl spaces 1.
What drives the cost of fixing or rebuilding a stair
We do not publish stair prices. The drivers are whether the stringers can be kept, whether the opening in the floor above must grow to give headroom, the stair shape (straight, L-shaped with a landing, or winders), materials, and finish work such as handrails and balusters.
Enlarging a floor opening often means new headers and joist work, which needs engineering and a permit.
Small fixes, such as adjusting the first or last riser to match, cost far less than a new stair, so measure early. Our cost guide explains contingencies for surprises like this, and the timeline tool shows where stair work falls in a project.
A well-built stair lasts as long as the house; finish treads and handrails wear and can be replaced.
How a new or rebuilt stair moves through a remodel
- Measure total rise and available run; sketch the stair with the IRC limits 1.
- If the floor opening must change, have an engineer design the framing.
- Apply for the permit; stair work is structural and life-safety work in most jurisdictions.
- Cut and install stringers, treads and risers; fireblock between stringers at the top and bottom of the run 1.
- Inspector checks framing, riser and tread uniformity, headroom and landings.
- Install handrails and guards, then finish treads.
- Final inspection confirms finished dimensions, since flooring changes the end risers.
Keeping a stair safe
- Fix loose treads and nosings right away.
- Keep runners tight; loose carpet changes the effective tread.
- Keep lights working at top and bottom.
- Check handrails for wobble and secure brackets into framing.
- Keep stairs clear of stored items.
Warning signs of a stair problem
- One step that feels different, often the top or bottom after new flooring.
- Treads under 10 inches or risers over 7-3/4 inches in an old stair 1.
- Missing handrail on a flight with four or more risers 1.
- Low headroom where people duck at the same spot.
- Sagging or cracked stringers, or treads that flex.
Stairs are structural and life-safety work
Changing a stair often means cutting floor joists to enlarge the opening, which needs an engineered design, a permit and a licensed contractor. Do not cut joists or stringers without that. Stair-related injuries lead to about a million U.S. emergency visits a year 4.
Structural signs, such as sagging stringers, call for a contractor or engineer. Dimensional issues are worth raising with a contractor before any remodel near the stair.
Code rules: 2021 IRC R311.7, IBC 1011 and IEBC 503
2021 IRC (new work in houses). Section R311.7.5.1 limits riser height to 7-3/4 inches and the difference between the largest and smallest riser in a flight to 3/8 inch; open risers more than 30 inches above the floor below may not pass a 4-inch sphere.
Section R311.7.5.2 requires treads of at least 10 inches with the same 3/8-inch tolerance. Section R311.7.5.3 sets nosings of 3/4 to 1-1/4 inches, not required where treads are at least 11 inches.
Sections R311.7.1, R311.7.2 and R311.7.3 set 36 inches of clear width, 6 feet 8 inches of headroom, and a maximum 12 feet 7 inches of rise per flight.
Section R311.7.6 requires landings, and R311.7.8 requires a handrail 34 to 38 inches high on flights with four or more risers 1.
2021 IBC (other buildings). Section 1011.5.2 sets risers of 4 to 7 inches and treads of at least 11 inches, with an exception for Group R-3 and similar occupancies 2.
2021 IEBC (existing buildings). Section 503.1, Exception 1, says an existing stairway need not comply with IBC Section 1011 where the existing space and construction does not allow a reduction in pitch or slope; Section 506.3 says the same for a change of occupancy 3.
Many jurisdictions apply similar logic to houses through local amendments or the IRC’s existing-building provisions, so ask your building department how it treats a replacement stair.
These are model codes; states and cities adopt editions and amend them. A licensed building official or ICC-certified inspector makes the call on your project.
Rise and run vs related stair rules
| Rule | What it controls | 2021 IRC value |
|---|---|---|
| Rise and run | Step height and depth | 7-3/4 in. max riser; 10 in. min tread 1 |
| Handrail requirements | Grip, height, continuity | 34 to 38 in. high on 4+ risers 1 |
| Guards | Fall protection at open sides | 36 in. at landings; 34 in. on stair sides 1 |
| Headroom | Clearance overhead | 6 ft 8 in. 1 |
| Stair width | Clear passage | 36 in. above handrail height 1 |
| Glazing near stairs | Safety glass in hazardous locations | Within a 60 in. arc of the bottom nosing and under 36 in. high 1 |
Stair myths
- Myth A small difference between steps does not matter.
- Reality The IRC caps the difference at 3/8 inch in a flight because feet expect each step to match 1.
- Myth House stairs follow the 7/11 rule.
- Reality That is the IBC rule for most buildings; houses under the IRC allow 7-3/4 inch risers and 10 inch treads 12.
- Myth Carpet counts toward tread depth.
- Reality IRC dimensions exclude carpets, rugs and runners 1.
- Myth Old stairs must always be rebuilt to current code.
- Reality The IEBC lets existing stairs stay where space does not allow a gentler slope; local rules decide 3.
- Myth Spiral stairs follow the same numbers.
- Reality Spiral stairs have their own limits, such as 9-1/2 inch risers 1.
How stair rules change by place
Stair geometry has no climate variable; the local variable is the code edition and its amendments. Each state adopts its own IRC edition and some amend stair dimensions or the treatment of existing stairs.
For example, Minnesota’s amendment to the IEBC lets existing stairs remain with risers up to 8-1/4 inches and runs of at least 9 inches, and lets a replacement stair keep its original rise and run where meeting those limits is technically infeasible 5.
Ask your building department which edition applies and how it treats a replacement stair before design. Exterior stairs in snowy places also need attention to drainage on landings, which the IRC allows to slope up to 1 in 20 where water must drain 1.
When to fix rise and run, and what to do next
Fix it when you are finishing a basement, adding a floor or attic room, or changing floor heights at either end of a stair. Those are the moments when the stair is inspected and when the cost of getting it right is lowest.
Start by measuring the total rise and the space you have, then run the example math above. If the result does not fit, talk with a designer about an L-shaped stair with a landing or winders, and with an engineer about enlarging the opening. Our guide to choosing a remodeling contractor helps with the hire.
- If New stair in an addition or attic
- Then Design to IRC R311.7 from the start
- If Existing stair, only end risers off after new flooring
- Then Adjust the top or bottom riser to within 3/8 inch
- If Existing stair steeper than code, space is fixed
- Then Ask the building official about the existing-stair allowance
- If Floor opening too small for headroom
- Then Engineer the opening before redesigning the stair
Questions about Stair Rise and Run
What is the maximum stair riser height for a house?
Under the 2021 IRC, a riser may be no more than 7-3/4 inches, measured between the leading edges of adjacent treads. The tallest and shortest risers in a flight may differ by no more than 3/8 inch. Your state or city may amend this, so check the code edition your building department uses.
What is the minimum stair tread depth?
The 2021 IRC requires treads of at least 10 inches, measured horizontally between the front edges of adjacent treads. Treads in a flight must match within 3/8 inch. If a tread is less than 11 inches deep, the stair also needs a nosing that projects 3/4 to 1-1/4 inches.
How do you calculate stair rise and run?
Measure the total rise from finished floor to finished floor. Divide it by 7.75 inches and round up to get the number of risers. Divide the total rise by that number for the actual riser height. Treads are one fewer than risers; multiply by the tread depth for the total run.
What is the 7-11 rule for stairs?
It refers to a 7-inch maximum riser and 11-inch minimum tread, the limits the 2021 International Building Code sets for most non-residential and multifamily stairs. Houses built under the IRC may use steeper stairs, up to 7-3/4 inch risers and 10-inch treads.
How much can stair steps vary?
No more than 3/8 inch. The 2021 IRC says the greatest riser height in a flight may not exceed the smallest by more than 3/8 inch, and the same tolerance applies to tread depth and to nosing projection. New flooring at the top or bottom often breaks this rule.
Do I have to bring old stairs up to code in a remodel?
Not always. The 2021 IEBC says an existing stairway need not comply with current stair rules where the existing space and construction do not allow a reduction in pitch. How your jurisdiction applies that to a house varies, so ask the building official before you plan the work.
What headroom is required over stairs?
The 2021 IRC requires at least 6 feet 8 inches of headroom, measured vertically from the sloped line connecting the tread nosings, or from the landing floor. Spiral stairs may have 6 feet 6 inches. Low headroom often means the floor opening above must be enlarged.
Does carpet count in stair measurements?
No. The 2021 IRC says riser and tread dimensions are measured exclusive of carpets, rugs and runners. Measure to the hard surface of the tread. Thick carpet can still make treads feel shorter, so consider it in design even though it is not counted.
How many steps need a handrail?
Under the 2021 IRC, a handrail is required on at least one side of each flight with four or more risers. It must be 34 to 38 inches above the line connecting the nosings and continuous for the full flight, with grip sizes set by the code.
Sources
- ICC, 2021 International Residential Code, Chapter 3 Building Planning (R302.11, R308.4.7, R311.7, R312.1.2), retrieved .
- ICC, 2021 International Building Code, Chapter 10 Means of Egress (1011.5.2), retrieved .
- ICC, 2021 International Existing Building Code, Chapter 5 Prescriptive Compliance Method (503.1 Exception 1, 506.3), retrieved .
- Blazewick DH et al., Stair-related injuries treated in United States emergency departments, Am J Emerg Med 2018;36(4):608-614 (PubMed abstract), retrieved .
- Minnesota Administrative Rules 1311.0503 (state amendment on existing stairways), retrieved .
Expert review
Written by the HyreRemodel Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Riser, tread, nosing, width, headroom, landing, handrail, guard and glazing rules were read from 2021 IRC Chapter 3 on ICC Digital Codes; IBC limits from 2021 IBC Section 1011.5.2; the existing-stair allowance from 2021 IEBC Sections 503.1 and 506.3.
Injury figures come from the Blazewick et al. abstract on PubMed. The layout example is our arithmetic on the IRC limits. This page is held noindex until an ICC-certified inspector or building official reviews it. No prices are given.
Suggest a correction. We fix errors and say what changed.