Stair Calculator
Calculate riser count, tread count, total run, and approximate stringer length from total rise and target riser height. One shared length unit for all stair dimensions. Basic geometry only — verify local code.
Quick answers
What is the maximum stair rise?
The IRC limits a residential riser to 7 3/4 in (196 mm); the IBC limits a commercial riser to 7 in (178 mm). Both codes also cap the variation within one flight: the tallest riser may not exceed the shortest by more than 3/8 in. That uniformity rule is where stairs most often fail inspection, because every individual riser can be under the maximum and the flight still not comply.
Riser and tread limits by code
| Standard | Max riser | Min tread | Variation in one flight |
|---|---|---|---|
| IRC (one- and two-family homes) | 7 3/4 in | 10 in | 3/8 in |
| IBC (commercial and public) | 7 in | 11 in | 3/8 in |
This calculator produces geometry, not a compliance ruling. Local jurisdictions amend these figures, so confirm with your building department before cutting stringers.
How many steps do you need for a 19 inch rise?
Three risers of 6.33 in each. Two risers would need 9.5 in apiece, well over the 7 3/4 in residential maximum, so three is the minimum that complies. Three risers give two treads, because a flight that lands on a floor always has one fewer tread than riser.
What is a comfortable stair rise and run?
Around 7 in of rise with a 10 to 11 in tread is the usual comfortable target in residential work, which is why 7 in is this calculator's default. The classic checks are that rise plus run falls near 17 to 18 in and that twice the rise plus the run lands near 25 in. A taller riser saves floor space and costs noticeably more effort to climb.
How do you calculate rise and run for stairs?
Divide total rise by your target riser height and round up to get the riser count, then divide total rise by that count for the actual riser. Treads are always one fewer than risers, total run is treads multiplied by tread depth, and the stringer is the diagonal, the square root of rise squared plus run squared. Rounding up matters: it is what keeps every riser equal and under the maximum.
Assumptions
- Straight flight with uniform risers and treads.
- Target riser near 7 in (≈178 mm) is common in US residential work.
- Does not verify IRC or local code compliance.
- Landing platforms and headroom are not calculated.
- Total rise is floor-to-floor vertical distance.
- Stair width is optional and informational only.
Number of risers = ceil(total rise ÷ target riser height). Actual riser = total rise ÷ risers. Treads = risers − 1. Total run = treads × tread depth. Stringer ≈ √(rise² + run²). All lengths use your selected unit (converted via meters/inches internally).9 ft total rise, 7 in target riser
- Enter total rise as 108 in (or 9 ft with unit Feet — values convert). Risers = 108 ÷ 7 ≈ 15.4 → 16 risers (ceil). Actual riser = 108 ÷ 16 = 6.75 in. Treads = 15. Run = 15 × 10 in tread = 150 in. Stringer ≈ √(108² + 150²) ≈ 184.9 in.
What is the maximum stair riser height allowed by code?
Under International Residential Code Section R311.7.5.1 the maximum riser height in a dwelling is 7-3/4 inches (196 mm), measured vertically between the leading edges of adjacent treads, and the greatest riser height within any flight may not exceed the smallest by more than 3/8 inch (9.5 mm) [1]. Minimum tread depth is 10 inches (254 mm) under R311.7.5.2, measured horizontally between the vertical planes of the foremost projection of adjacent treads and at a right angle to the leading edge, with the same 3/8-inch uniformity limit [1]. Those two figures define the steepest legal residential stair: 7-3/4 up, 10 across.
Local codes govern. Jurisdictions adopt different IRC editions and amend them, some states permit or require different riser and tread limits, and commercial stairways under the IBC are shallower and wider than residential ones. This calculator is pure geometry: it divides your total rise into equal risers, subtracts one for the tread count, and multiplies treads by the depth you enter. It does not verify code compliance and does not check handrails, guards, landings, headroom, illumination, or stringer structure. Confirm the adopted code edition and any local amendments with your building department before cutting a stringer.
How do you calculate the number of steps for a given total rise?
Divide the total rise by your target riser height and round up to the next whole number, then divide the total rise by that count to get the actual riser. For a 108-inch floor-to-floor rise with a 7-inch target: 108 ÷ 7 = 15.43, round up to 16 risers, and 108 ÷ 16 = 6.75 inches per riser. Rounding up always pushes the actual riser below your target, which is the safe direction against the 7-3/4-inch maximum. Treads number one fewer than risers on a straight flight, because the upper floor serves as the final tread, so 16 risers give 15 treads.
Multiply treads by tread depth for the total horizontal run. Fifteen treads at 10 inches is 150 inches, or 12 ft 6 in of floor space — often the binding constraint in a remodel. Widen the tread to 11 inches and the same flight needs 165 inches. Measure total rise from finished floor to finished floor, including underlayment, tile, and hardwood on both levels; an unplanned 3/4-inch flooring buildup at the top is the most common cause of one odd riser. Enter every dimension in the same unit and let the tool convert when you change the unit selector.
How much headroom does a staircase need?
IRC R311.7.2 requires minimum headroom of 6 feet 8 inches (2,032 mm) in all parts of the stairway, measured vertically from the sloped plane adjoining the tread nosing or from the floor surface of the landing or platform [1]. Spiral stairs are treated separately: R311.7.10.1 permits a 26-inch minimum width with each tread having a 7-1/2-inch minimum depth measured 12 inches from the narrower edge, a rise of no more than 9-1/2 inches, and reduced headroom of 6 feet 6 inches [1]. Stairways must also be at least 36 inches (914 mm) in clear width above the permitted handrail height and below the required headroom height [1].
Two more dimensions constrain layout. A flight of stairs may not have a vertical rise greater than 12 feet (3,658 mm) between floor levels or landings, and every landing must measure at least 36 inches (914 mm) in the direction of travel and be no narrower than the stairway it serves [1]. The American Wood Council's prescriptive deck guide repeats both rules for exterior stairs and requires an intermediate landing once the total vertical height of a stairway exceeds 12 ft 0 in [2]. Handrails are required on any flight with four or more risers and must sit 34 to 38 inches above the sloped nosing plane [1][2].
How long does a stair stringer need to be for a 9 foot rise?
Use the Pythagorean theorem on rise and run. A 9-foot (108-inch) total rise divided into 16 risers of 6.75 inches gives 15 treads; at a 10-inch tread depth the total run is 150 inches. Stringer length is the square root of 108² + 150² = 11,664 + 22,500 = 34,164, so the stringer measures about 184.8 inches — 15 ft 5 in, the named result. Buy 16-foot stock and expect to trim. The pitch is arctan(108 ÷ 150) ≈ 35.8° from horizontal, comfortably inside the range most people read as a normal house stair.
That calculated diagonal is a minimum. Add length for the plumb cut at the top, the level cut at the bottom, any bearing block, and the notch geometry if you are cutting a sawtooth or housed stringer. The American Wood Council's deck guide requires exterior stair stringers of at least 2×12 nominal stock, limits stringer span, and allows a notched-and-bolted 4×4 post or an intermediate landing to shorten a long span [2]. Cutting a sawtooth notch removes material at the throat of the stringer, which is exactly why those span limits exist — have anything unusual verified by a designer.
Why must all stair risers be the same height?
Because people climb stairs by rhythm, not by sight. The IRC limits the difference between the largest and smallest riser in a flight to 3/8 inch (9.5 mm), and applies the same 3/8-inch limit to tread depth, to winder tread depth measured at the 12-inch walk line, and to nosing projection between two stories including the nosing at floors and landings [1]. A single riser outside tolerance is a recognized trip hazard and one of the most frequently cited stair defects at inspection. Uniformity is also why this calculator divides the rise into equal parts instead of letting you absorb a remainder in one step.
The remainder usually shows up at the bottom. If you frame from the top down and forget that the lowest riser sits on a slab that will later receive 1/2-inch tile, that riser finishes 1/2 inch short of every other one. The fix is to recompute the whole flight from finished floor to finished floor, not to shave one tread. Related uniformity details: nosing must project not less than 3/4 inch and not more than 1-1/4 inches on stairways with solid risers, is not required where tread depth is at least 11 inches, and the leading-edge radius may not exceed 9/16 inch [1].
How to measure
Measure vertical distance from finished floor to finished floor (or landing). Enter rise, riser, and tread in the same unit — inches for framing precision, or feet/meters for whole-story heights. Switching the unit converts all fields so 108 inches never becomes 108 feet.
What are the IRC stair dimension limits for homes?
| Requirement | IRC limit | Metric | Section |
|---|---|---|---|
| Maximum riser height | 7-3/4 in | 196 mm | R311.7.5.1 |
| Minimum tread depth | 10 in | 254 mm | R311.7.5.2 |
| Maximum variation within a flight | 3/8 in | 9.5 mm | R311.7.5.1 and R311.7.5.2 |
| Minimum headroom | 6 ft 8 in | 2,032 mm | R311.7.2 |
| Minimum clear stairway width | 36 in | 914 mm | R311.7.1 |
| Maximum vertical rise per flight | 12 ft | 3,658 mm | R311.7.6 |
| Handrail height above nosing plane | 34 in to 38 in | 864 mm to 965 mm | R311.7.8.1 |
Values from a building-department guide to the 2018 IRC. Locally adopted editions and amendments govern the actual project.
How many risers do you need for common floor-to-floor heights?
| Total rise | Risers at a 7 in target | Actual riser height | Treads | Total run at 10 in tread |
|---|---|---|---|---|
| 96 in (8 ft) | 14 | 6.86 in | 13 | 130 in |
| 105 in | 15 | 7.00 in | 14 | 140 in |
| 108 in (9 ft) | 16 | 6.75 in | 15 | 150 in |
| 112 in | 16 | 7.00 in | 15 | 150 in |
| 120 in (10 ft) | 18 | 6.67 in | 17 | 170 in |
| 126 in | 18 | 7.00 in | 17 | 170 in |
| 132 in (11 ft) | 19 | 6.95 in | 18 | 180 in |
Riser count is rounded up, which keeps the actual riser below the target and below the 7-3/4 in code maximum.
How does stringer length change with rise and run?
| Total rise | Total run | Stringer diagonal | Pitch from horizontal |
|---|---|---|---|
| 84 in | 110 in | 138.4 in | 37.4° |
| 96 in | 130 in | 161.6 in | 36.4° |
| 108 in | 150 in | 184.8 in | 35.8° |
| 120 in | 170 in | 208.1 in | 35.2° |
| 132 in | 180 in | 223.2 in | 36.3° |
| 144 in | 200 in | 246.4 in | 35.8° |
Diagonal is the square root of rise squared plus run squared. Add material for end cuts, bearing blocks, and notch depth.
Common mistakes
- Measuring to subfloor instead of finished floor height.
- Unequal risers after adjusting only the bottom step.
- Ignoring maximum riser height and minimum tread depth in local code.
- Changing the length unit without converting values (this tool converts automatically).
Frequently asked questions
What is the maximum riser height for residential stairs?
What is the minimum tread depth for stairs?
How much headroom is required above a staircase?
How many stairs do I need for a 9 foot rise?
Can stair risers be different heights?
How do you calculate stair stringer length?
Is this stair calculator code compliant?
Sources and references
Last updated:
- 2018 Residential Stair Guide, IRC Section R311.7 (riser, tread, headroom, width, landing, handrail requirements) — Town of Timnath, Colorado Building Department (2018)
- DCA 6: Prescriptive Residential Wood Deck Construction Guide (stair, stringer, landing, and handrail requirements) — American Wood Council (2015)
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