Last updated: 2026-09-24
Quick Answer
Enter your total rise - the finished floor-to-floor height in inches - and the calculator handles the rest: riser count, exact riser height, treads, stringer length and cuts, and the stairwell opening needed for 6'8" headroom. An 8-foot ceiling plus a 10"-12" floor system is about 106"-108" of rise, which works out to 14 risers of 7-9/16" to 7-11/16". All results are flagged against IRC 2021 requirements.
Inputs you'll need
- Total rise: finished floor to finished floor, in inches
- Target riser height (default 7.5", IRC max 7.75")
- Tread run, nosing to nosing (default 10.5", IRC min 10")
- Nosing overhang (3/4" to 1-1/4" when the run is under 11")
- Closed or open risers
- Stair width (IRC min 36" clear)
- Where the stair goes: through a floor (interior) or up to a deck
- Upper floor thickness, for the stairwell opening (interior stairs)
- Top of the stringer: one step down (standard) or flush with the floor
Related tools: Deck Railing Calculator, Framing Cost Calculator, and Board Foot Calculator.
Finished floor to finished floor. An 8' ceiling plus a 10"-12" floor system above is about 106"-108".
Code max 7-3/4". Most stairs: 7"-7-1/2".
Nosing to nosing, not the board depth. Code min 10".
Code min 36"
3/4"-1-1/4" (required under an 11" run)
Interior stair under a floor: we size the stairwell opening for 6'8" headroom.
Top tread is one step below the upper floor; the floor is the last step. Most common.
Your stair
Risers
14
steps up
Treads
13
the floor is the top step
Each riser
7‑11/16"
Each tread run
10‑1/2"
Riser adjusted from 7-1/2" to 7-11/16" so every step comes out equal.
Key measurements
Side view, drawn to scale
Laying out the stringer on the 2x12
Mark notch 1 at 5" from the bottom end, then measure every notch from that first mark (don't add up one step at a time):
Cutting the stringer (bottom two steps, close up)
Cut it in this order
- 1Sight down the 2x12 and put the crown (the hump) up. The notches go on that edge.
- 2Clamp stair gauges on your framing square: 7-11/16" on the tongue (rise), 10-1/2" on the blade (run).
- 3Mark 13 notches along the edge. Measure each one from the first mark using the list, so small errors don't add up.
- 4Mark the floor cut (level) at the bottom and the plumb cut at the top.
- 5Cut the first rise 1" short (6-11/16"), the tread thickness, so every finished step is 7-11/16".
- 6Cut the notches with a circular saw, stop at the inside corners and finish with a handsaw or jigsaw.
- 7Test-fit this stringer, then use it as the pattern for the other 2.
How the numbers are worked out
- 1
How many risers
108 ÷ 7.5 = 14.4 → 14 risers (rounded to the nearest whole step)
- 2
Exact riser height
108 ÷ 14 = 7.714" → 7-11/16"Rounding to 1/16" is short by 3/8" over 14 steps. Mark the heights from the list below instead of stepping off one setting, or the top step comes out tall.
- 3
How many treads
14 − 1 = 13 treads (the upper floor is the top step)
- 4
Total run
13 × 10.5 = 11' 4-1/2"
- 5
Stringer length
√(108² + 136.5²) = 14' 6-1/16". The cut stringer fits in 14' 5-1/2" of board; with 2" to trim, buy 16' 2x12s.
- 6
Bottom cut (stringer drop)
7.71 − 1 tread = 6-11/16" for the first rise on the stringer
- 7
Wood left under the notches
11-1/4" board − 6.22 notch depth = 5-1/16" (5" or more is the target)
- 8
Stairwell opening
1 nosing + (80 + 12 floor) × 10.5 ÷ 7.71 = 10' 6-1/4", measured back from the top of the stair
Story pole: top of each tread, measured from the floor
Mark these on a straight board (or the stringer) so rounding never adds up.
IRC code checks
Rules of thumb (not code)
Check with your local building department; some areas amend the IRC.
| Item | Qty | Size |
|---|---|---|
| Stringers, 2x12 (about 18" apart) | 3 | 16' |
| Treads (run + nosing deep) | 13 | 11-1/2" × 36" |
| Riser boards | 14 | 7-11/16" × 36" |
Stringer count follows the American Wood Council deck guide (DCA 6): at least three cut stringers, no more than 18" apart. Riser boards are ripped to fit under each tread; add 10-15% for waste and defects.
Quick Answer
For a 9' 0" floor-to-floor rise you need 14 risers at 7-11/16" each and 13 treads at 10-1/2". Total run: 11' 4-1/2". Stringer length: 14' 6-1/16"; stairwell opening at least 10' 6-1/4".
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Stair Design & Code Guide
Building code requirements and calculation methods for residential stairs.
Standard Stair Dimensions & Building Code
IRC residential code requires a maximum 7-3/4" rise and minimum 10" run per step, with minimum 36" width for interior stairs.
- Maximum riser height: 7-3/4" (7.75 inches)
- Minimum tread depth: 10 inches (nosing not counted)
- Minimum width: 36 inches clear above handrail height
- Maximum variation: 3/8" between tallest and shortest riser
- Headroom: Minimum 6'-8" clearance above the stair nosing line
- Handrail height: 34"–38" measured from stair nosing
The comfort rule: 2 × Riser + Tread = 24"–25". A 7" rise with an 11" tread (25") is considered ideal.
Key Takeaways
- Max riser: 7-3/4", min tread: 10"
- Min width: 36" clear (residential)
- Comfort rule: 2 × Rise + Tread = 24"–25"
How to Calculate Number of Stairs
Divide total rise (floor-to-floor height) by desired riser height to determine the number of steps needed.
- Typical floor-to-floor height: about 106"–108" with an 8' ceiling, about 118" with a 9' ceiling (ceiling height plus the floor framing above)
- Example: 108" total rise ÷ 7.5" per riser = 14.4 → round to 14 risers
- Actual riser: 108" ÷ 14 = 7.71" per step (within code)
- Number of treads: one fewer than risers when the top of the stringer is one step down (14 risers = 13 treads); equal to risers with a flush top
- Total run: 13 treads × 10" = 130" (10'-10") horizontal distance needed
Always measure actual floor-to-floor height, not assumed height. A 1/2" measuring error doesn't spread out; it all lands in the top or bottom step, which is more than the 3/8" riser variation the IRC allows.
Key Takeaways
- Number of risers = total rise ÷ riser height
- Treads = risers minus 1 (standard top), or equal to risers (flush top)
- Always measure actual floor-to-floor (not assumed)
Worked examples: common stair configurations
These show how the math works for typical residential scenarios. Run them through the calculator above to verify.
| # | Scenario | Calculation |
|---|---|---|
| 1 | Interior stairs, 97" total rise |
Risers = round(97 / 7.5) = 13 Actual riser = 97 / 13 = 7.46" (IRC pass) Treads = 13 - 1 = 12 Total run = 12 × 10.5" = 126" (10.5 ft) Stringer length = sqrt(97² + 126²) = 159.0" Order 3 stringers, 14 ft 2×12s (the cut stringer fits in about 158-1/2") |
| 2 | Deck stairs, 4-ft deck height (48" total rise) |
Risers = round(48 / 7.5) = 6 Actual riser = 48 / 6 = 8.0" -- fails IRC (max 7.75") Adjust to 7 risers: 48 / 7 = 6.86" (IRC pass) Treads = 7 - 1 = 6 Total run = 6 × 10.5" = 63" (5.25 ft) Stringer length = sqrt(48² + 63²) = 79.2" - order 8 ft 2×12s |
Quick-reference: rise vs. stringer lumber by floor height
Stringer length is always longer than total run or total rise - it's the hypotenuse. The cut stringer fits in about that length of board; buy the next even length.
| Example | Total rise | Risers | Riser height | Total run (10.5" treads) | Stringer length | 2×12 to buy |
|---|---|---|---|---|---|---|
| 97" (low basement) | 97" | 13 | 7-7/16" | 126" (10.5 ft) | ~159" | 14' |
| 8' ceiling + framing | 108" | 14 | 7-11/16" | 136.5" (11.4 ft) | ~174" | 16' |
| 9' ceiling + framing | 118" | 16 | 7-3/8" | 157.5" (13.1 ft) | ~197" | 18' |
| Deck, 3 ft | 36" | 5 | 7-3/16" | 42" (3.5 ft) | ~55" | 8' |
| Deck, 4 ft | 48" | 7 | 6-7/8" | 63" (5.25 ft) | ~79" | 8' |
Stair layout mistakes worth avoiding
- Measuring rise from subfloor instead of finished floor. If you're adding flooring at top or bottom, it changes the total rise. Measure from finished surface to finished surface, or account for the flooring thickness in your calc.
- Rounding the riser count down. If 97" divided by 7.5" gives 12.93 risers, you need 13 risers - not 12. Using 12 pushes each riser to 8.08" which fails IRC code.
- Stepping off one rounded riser setting. 108" ÷ 14 = 7.714", which rounds to 7-11/16". Step that off 14 times and you land at 107-5/8", 3/8" short, so the top step comes out 8-1/16" (over code). Mark each tread height from the floor instead (the calculator lists them).
- Not checking stringer throat depth. After cutting the notches for treads and risers, the solid wood left under the deepest notch (the throat) should be about 5" or more on a 2×12 (the basis of the American Wood Council deck guide, DCA 6). Go too deep and the stringer is structurally compromised.
- Forgetting the landing at the top. With a standard (one step down) stringer, the upper floor is the top step, so treads = risers minus 1. A flush-mounted top adds one more tread and one more run. Easy to miss when planning footprint.
- Ordering stringers too short. Lumber comes in even lengths, and the cut stringer needs its full layout length plus a little to square the ends. A 159" stringer fits a 14-foot 2×12 (168"); a 12-foot (144") is too short.
- Ignoring headroom at the top of the stair opening. The 80" clearance applies along the entire stairway, including where the stair passes through the upper floor. Model it in the calculator before framing the opening.
Sources
Related tools
- Deck Railing Calculator - Linear feet of railing, post count, and balusters for any deck layout
- Framing Cost Calculator - Estimate labor and lumber costs for wall and floor framing
- Board Foot Calculator - Convert stringer and tread dimensions to board feet for pricing lumber
- Concrete Footing Calculator - Size footings and get concrete quantities for stair landings and posts
Once you have your stair layout dialed in, EstimationPro turns the job into a priced, line-item estimate. Send it from EstimationPro and it follows up with your client for you.
How to Use This Calculator
Measure the total rise
Measure the vertical distance from the finished floor at the bottom to the finished floor at the top. This is your total rise in inches. An 8-foot ceiling (96") plus a 10" to 12" floor system above works out to about 106" to 108".
Set riser and tread dimensions
Adjust the desired riser height (default 7.5") and tread depth (default 10.5"). The IRC requires a maximum 7.75" riser and minimum 10" tread. Set the nosing overhang: code requires 3/4" to 1-1/4" when the tread run is under 11".
Choose mount type and width
Choose whether the stair runs through a floor (interior) or up to a deck, and whether the top of the stringer sits one step down (standard) or flush with the floor (adds one tread and one run). Set stair width, minimum 36" per IRC. For interior stairs, enter the upper floor thickness so the stairwell opening is sized for 6'8" headroom.
Review code compliance and materials
Check green/red/yellow compliance badges for IRC requirements. Check the Lumber list for stringer, tread, and riser board quantities. Toggle Imperial/Metric or Fractions, and print results for the job site.
Stair Calculation Formulas
Number of Risers = Total Rise ÷ Target Riser Height, rounded to the nearest whole number
(if that makes a riser taller than 7-3/4", use one more riser)
Actual Riser Height = Total Rise ÷ Number of Risers
Number of Treads = Number of Risers − 1 (standard), or = Number of Risers (flush-mounted top)
Total Run = Number of Treads × Tread Run
Stringer Length = √(Total Rise² + Total Run²)
2×12 to Buy = the cut stringer's full length + 2" to trim, rounded up to an even number of feet
First Rise Cut on the Stringer = Riser Height − Tread Thickness
Stairwell Opening = Nosing + (80" + Upper Floor Thickness) × Tread Run ÷ Riser Height
(+ one Tread Run for a flush-mounted top)
Riser + Tread Comfort Rule: Riser Height + Tread Run = 17" to 18" (rule of thumb, not code)Where:
- Total Rise
- = Vertical distance from finished floor to finished floor (inches)
- Total Run
- = Horizontal distance from first riser to last riser (inches)
- Riser + Tread
- = Should equal 17" to 18" for comfortable stairs (comfort rule)
- Min Headroom
- = 80 inches (6 feet 8 inches) per IRC R311.7.2
- Max Riser Height
- = 7.75 inches per IRC R311.7.5.1
- Min Tread Depth
- = 10 inches measured nosing-to-nosing per IRC R311.7.5.2
- Nosing
- = 3/4" to 1-1/4" required when tread depth < 11" per IRC R311.7.5.3
- Min Width
- = 36 inches clear per IRC R311.7.1
Stair Building Code Quick Reference (IRC 2021)
| Requirement | IRC Code | Value |
|---|---|---|
| Maximum Riser Height | R311.7.5.1 | 7.75" |
| Minimum Tread Depth | R311.7.5.2 | 10" |
| Nosing (tread < 11") | R311.7.5.3 | 3/4" to 1-1/4" |
| Maximum Riser Variation | R311.7.5.1 | 3/8" |
| Minimum Width | R311.7.1 | 36" |
| Minimum Headroom | R311.7.2 | 6'8" (80") |
| Handrail Height | R311.7.8.1 | 34" to 38" |
| Guard Required (drop > 30") | R312.1.1, R312.1.2 | 36" min (34" min on open sides of stairs, from the nosing line) |
| Open risers (more than 30" up) | R311.7.5.1 | Gap must not pass a 4" sphere |
| Max rise of one flight | R311.7.3 | 151" (12'7") |
Stair Terminology Glossary
- Riser --
- The vertical board between treads. Riser height is the vertical distance from one tread surface to the next.
- Tread --
- The horizontal surface you step on. Depth is measured from the front edge (nosing) to the back where the next riser meets.
- Stringer --
- The diagonal structural member (typically 2×12 lumber) that supports the treads and risers. With cut stringers, use at least 3, no more than 18" apart.
- Nosing --
- The front edge of a tread that projects past the face of the riser below. Required by IRC when tread depth is less than 11 inches.
- Total Rise --
- The total vertical distance from the finished floor at the bottom to the finished floor at the top of the stairway.
- Total Run --
- The total horizontal distance of the stairway, calculated as the number of treads multiplied by the tread depth.
- Throat --
- The narrowest point of a notched stringer, measured perpendicular to the stringer edge. On a cut 2×12, aim for about 5" or more (the basis of the American Wood Council deck guide, DCA 6).
- Stairwell Opening --
- The rectangular hole in the upper floor that the stairway passes through. Must be large enough to maintain 80" headroom clearance.
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Frequently Asked Questions
What is the maximum riser height allowed by code?
What is the minimum tread depth for stairs?
How do I calculate stringer length?
What is the riser plus tread rule?
How much headroom do stairs need?
How many stairs do I need for a 9-foot ceiling?
What is the difference between standard and flush mount stringers?
How wide do residential stairs need to be?
How do I calculate stairwell opening size?
What size lumber do I need for stair stringers?
How many stairs do I need for 8 feet of rise?
What is the rise and run for deck stairs?
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- How to Estimate Construction Jobs: A Step-by-Step System
- Construction Takeoff: How to Do a Quantity Takeoff
Values are from the 2021 IRC. Many jurisdictions amend it, so confirm with your local building department.
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