Stair Calculator (Rise, Run and Stringers)

A staircase calculator and stair builder: steps, exact rise and run, stringer length, landings and a cut list, checked against code.

Project Details
Enter your measurements and requirements
Results
Calculated estimates for your project
Risers (steps)13
Riser height7-3/8" (7.385 in)
Treads12 at 10"
Total run120" (10' 0")
Stringer length153-11/16" (12' 9-11/16"), cut from a 14 ft 2x12
Angle36.4 degrees
Stringers4
Comfort (2R + T)24-3/4" (comfortable)
Code checkPasses IRC R311.7
Rough materials cost$392

Turn these numbers into a build plan.

  • 13 at 7.38" risers
  • 10" tread depth
  • 120.0" total run
Materials List
Recommended materials and quantities
Stringers, PT 2x12 x 14 ft4 ($179)
Treads, 5/4x6 x 8 ft deck boards (2 per tread)9 ($99)
Risers, 1x8 x 8 ft (optional, closed risers)5 ($45)
Stringer hangers or ties4 ($24)
Structural and deck screws1 box each ($45)
7-3/8" rise10"Total run 120"13 risers, 36.4 degThroat 5-5/16"
Drop the bottom of the stringer by the tread thickness: first riser cuts to 6-3/8".
Other riser counts for the same rise
RisersRiserRunCode
128"110" (9' 2")Fails
137-3/8"120" (10' 0")Passes
146-7/8"130" (10' 10")Passes

Turn this into a build plan in Blueprint: the cut list becomes a shopping list, the stringer layout a step-by-step checklist, and the measurements go with you to the lumber yard on your phone. Need the framing square marks for every step? Open the stair stringer calculator. Pouring a pad at the bottom? Use the concrete stairs calculator or sonotube calculator.

Next you will need

Stair Stringer CalculatorLumber Calculator

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Project plan · built from your numbers

13-riser stair, 96" total rise

13 risers at 7.38" and 12 treads at 10" for a 120.0" total run, built on 4 cut 2x12 stringers.

Materials
$552
Time
2 weekends
Level
Advanced
8 steps 9 tools 7 materials
  1. 1

    Confirm code and permit

    Most codes cap rise at 7-3/4" and require a 10" minimum tread, with all risers within 3/8" of each other. Your layout is 7.38" by 10". Stairs attached to a deck or house usually need a permit, so check before buying lumber.

    • Rise and run within local code
    • Permit pulled if required
    • Handrail and guard rules noted
  2. 2

    Measure the real total rise

    Set a level straightedge off the top landing and measure straight down to where the bottom stair lands. Re-run the numbers if it differs from 96".

    • Rise measured at the landing spot
    • Landing level and solid
    • Landing pad placed
  3. 3

    Lay out the first stringer

    Clamp stair gauges to the framing square at 7.38" and 10". Mark 12 treads and 13 risers along the board, then cut the bottom riser to 6.38" (one tread thickness less) so every step comes out even.

    • All marks from the same board edge
    • Bottom riser dropped by tread thickness
    • Top plumb cut marked
01 · Your numbers
Risers
13 at 7.38"
Tread depth
10"
Total run
120.0"
Est. cost
$552
02 · The plan

8 steps · 9 tools · 7 materials

5 more steps, the full tool list and a shopping list you can check off as you go.

03 · Finished

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13-riser stair, 96" total rise

Finished in 2 weekends · $552 DIY

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Borrow these 9 tools from neighborsFull how-to guide: Build stairs

How to calculate stairs

Worked example: a 96 in rise with a 7-1/2 in target riser is 96 / 7.5 = 12.8, so 13 risers of 7-3/8" (7.38 in). That gives 12 treads of 10 in for a 120 in run, and a 12' 9-11/16" stringer cut from a 14 ft 2x12.

  1. Measure the total rise. Finished floor to finished floor, or deck surface to the ground where the bottom step lands, on a level line.
  2. Count the risers. Divide the rise by your target riser (7 to 7-3/4 in) and round up. Exact riser = rise / risers.
  3. Set the tread and run. Treads = risers minus 1. Total run = treads x tread depth (10 in or more).
  4. Check comfort and code. 2 x riser + tread should land between 24 and 25 in, riser 7-3/4 in max, tread 10 in min, headroom 6 ft 8 in.
  5. Lay out and cut the stringers. Mark the riser and tread with a framing square and stair gauges, drop the bottom by the tread thickness, cut one, test it and copy it.

Rise and run rules

Keep every riser within 3/8 in of the others, 7-3/4 in or less, and every tread 10 in or more. Comfortable stairs land between 24 and 25 in on 2R + T: 7 in risers with 11 in treads (the 7-11 rule) or 7-1/2 in with 10 in. Steeper is a ladder; shallower wastes floor space and feels awkward.

Stair layout by total rise (7-3/4 in max riser, 10 in treads)
Total riseRisersRiserTreadsRunStringer
24 in46"330"3' 2-7/16"
36 in57-3/16"440"4' 5-13/16"
48 in76-7/8"660"6' 4-13/16"
60 in87-1/2"770"7' 8-3/16"
84 in117-5/8"10100"10' 10-5/8"
96 in137-3/8"12120"12' 9-11/16"
108 in147-11/16"13130"14' 1"
120 in167-1/2"15150"16' 1/16"
144 in197-9/16"18180"19' 2-1/2"

Stair code (IRC R311.7)

Model IRC R311.7 values; your city may amend them, so confirm with the building department
ItemRequirement
Riser height7-3/4 in max; risers within 3/8 in of each other
Tread depth10 in min, nosing to nosing
Nosing3/4 to 1-1/4 in where treads are under 11 in
Headroom6 ft 8 in min, measured from the nosing line
Width36 in min clear above the handrail
Handrail34 to 38 in above the nosings, on 4 or more risers
Guard36 in high where the side drops more than 30 in; openings under 4 in
Flight151 in max rise between floors or landings
LandingAt least as deep as the stair is wide, 36 in min

Stairs with a landing

Any flight rising more than 151 in needs a landing, and an L or U turn fits a long stair into a smaller room. Split the risers between the two flights, keep every riser the same height, and make the landing at least as deep as the stair is wide. Each flight gets its own stringers.

Deck stairs

Two 5/4x6 deck boards make an 11-1/4 in tread; pick the deck preset and the calculator uses it. Land the stringers on a concrete pad or pavers, never bare soil: size it with the concrete stairs calculator, the sonotube calculator or the footing rebar calculator. Four or more risers need a handrail.

Cutting the stringers

For framing square marks at every step, the first-riser drop and the throat left in the board, use the stair stringer calculator. The stair building cheat sheet walks through layout, hangers and treads, and the deck calculator prices the deck above.

Stair terms

TermMeaning
Total riseVertical distance from the lower finished floor to the upper one
RiserThe vertical part of a step, and its height
TreadThe horizontal part you step on; tread depth excludes the nosing
NosingThe tread's overhang past the riser below
RunHorizontal length of the whole stair
StringerThe notched board that carries the treads
ThroatWood left below the notches of a cut stringer
HeadroomClear height above the nosing line

Stair calculator FAQ

How many steps for an 8 ft rise?

96 in needs 13 risers of 7-3/8" (12 treads) at the 7-3/4 in maximum, or 14 risers of 6-7/8" for an easier climb.

How many steps for a 9 ft rise?

108 in needs 14 risers of 7-11/16" and 13 treads; 15 risers of 7-3/16" is gentler.

What is the ideal rise and run?

About 7 to 7-1/2 in rise and 10-1/2 to 11 in run. The 2R + T rule says twice the riser plus the tread should be 24 to 25 in; the old 7-11 rule (7 in rise, 11 in run) fits it.

How long is a stringer for N steps?

Stringer length = sqrt(total rise^2 + total run^2). A 4-step deck stair (30 in rise, 10 in treads) is about 3' 6-7/16"; buy an 8 ft 2x12.

When is a landing required?

When one flight rises more than 151 in (12 ft 7 in). A landing must be at least as deep as the stair is wide, 36 in minimum.

How many stringers for a 36 or 48 in wide stair?

With stringers 16 in on center, a 36 in stair takes 4 and a 48 in stair 5 (12 in on center for composite treads). Three is a common minimum for 36 in with 2x treads.

2x12 vs 2x10 stringers?

Use 2x12 for cut stringers: it keeps at least 3-1/2 in (often 5 in) of wood below the notches. A 2x10 is only enough for short flights or for housed stringers.

How do I calculate stairs with a landing?

Split the risers between the flights (the calculator puts the extra on the lower flight) and add the landing depth to the run. A 160 in rise with an L landing is 11 + 10 risers with the landing at 6' 11-13/16".

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