Free calculator
Stair Calculator: Rise, Run, Treads & Stringers
Enter your total rise and get the full stair layout — riser count and height, tread count, total run, stringer length, stair angle, and how many 2×12 stringers to buy. The math follows typical IRC guidance (7.75″ max riser) and every step is shown. The math runs entirely in your browser.
By HowMuchBuild Editorial TeamCalculation reviewedUpdated October 2026
Floor-to-floor (or ground-to-deck) height, measured vertically.
Deeper treads = more comfortable, longer run.
36″ is a typical residential minimum.
Based on typical International Residential Code guidance (7.75″ max riser, 10″ min tread). Stairs are safety-critical — verify riser, tread, handrail, and guard requirements with your local building department before you build.
Estimated cost
What will it cost?
Enter your local store prices — prices vary by region.
2×12 stringer boards
2 boards
—
Estimate — prices vary by store and region. Check your local store for current pricing.
Stair layout
5
risers
4
treads
7.20″
each riser
3 ft 8.0 in
total run
4 ft 8.9 in
stringer length
39.3°
stair angle
2
stringers (2×12)
3.7 ft
run in feet
How we calculated it
- Risers = ⌈36″ ÷ 7.75″ (IRC max)⌉ = 5 risers
- Actual riser = 36″ ÷ 5 = 7.20″ each
- Treads = 5 − 1 = 4; total run = 4 × 11″ = 44.0″
- Stringer length = √(36² + 44.0²) = 56.9″ (4 ft 8.9 in)
- Stair angle = atan(36 ÷ 44.0) = 39.3°
- Stringers = 2 (typical for a 36″ wide stair)
Code check: this tool counts risers and treads — it does not approve your stair. Riser/tread limits, handrails, guards, headroom, and landings are all regulated; requirements vary by jurisdiction and by whether the stair is interior, exterior, or egress. Verify with your local building department before you cut stringers.
Worked example: 36″ total rise, 11″ treads, 36″ wide
A small porch stair: 36 inches of total rise, 11-inch treads, 36 inches wide. Step by step:
- Risers: ⌈36″ ÷ 7.75″⌉ = ⌈4.65⌉ = 5 risers
- Actual riser height: 36″ ÷ 5 = 7.20″ each (under the 7.75″ max)
- Treads: 5 − 1 = 4 treads; total run = 4 × 11″ = 44″ (3 ft 8 in)
- Stringer length: √(36² + 44²) = √3,232 = 56.9″ (4 ft 8.9 in)
- Stair angle: atan(36 ÷ 44) = 39.3°
- Stringers: 36″ wide → 2 stringers, cut from 2×12 lumber
Riser count reference (7.75″ max)
How many risers common total rises need, and how tall each one ends up:
| Total rise | Risers | Each riser |
|---|---|---|
| 30″ | 4 | 7.50″ |
| 36″ | 5 | 7.20″ |
| 42″ | 6 | 7.00″ |
| 48″ | 7 | 6.86″ |
| 60″ | 8 | 7.50″ |
The formulas
Risers
Risers = ⌈ total rise ÷ 7.75″ ⌉ — round up so no single riser exceeds the IRC maximum. Actual riser = total rise ÷ risers — always round up the count, never the height.
Treads and total run
Treads = risers − 1 — the upper floor is the last “tread.” Total run = treads × tread depth. Deeper treads lengthen the run and flatten the stair angle.
Stringer length and angle
Stringer = √(rise² + run²) — the hypotenuse of the stair triangle. Angle = atan(rise ÷ run), converted to degrees. Each stringer is cut from one continuous 2×12 board.
Stringer count
2 stringers up to 36″ wide, 3 for wider stairs — typical layout guidance. Wide stairs and heavy use may need more; your local code governs.
Frequently asked questions
What is the maximum riser height allowed by code?
The International Residential Code (IRC) allows a maximum riser height of 7.75 inches and requires a minimum tread depth of 10 inches. The tallest and shortest risers in a flight must also be within 3/8 inch of each other. These are typical code figures — your local jurisdiction has the final word, so verify before you build.
How many stringers does my stair need?
As a typical layout, use 2 stringers for stairs up to 36 inches wide and 3 stringers for wider stairs. Very wide stairs may need more — stringer spacing rules vary, so check your local code. The calculator above applies the 2/3 rule from your stair width.
What is a comfortable stair angle?
Stair angle = arctangent(rise ÷ run). A 7-inch riser with an 11-inch tread gives about 32.5°, which most people find comfortable. Angles roughly between 30° and 37° feel normal for residential stairs; steeper than that starts to feel like a ladder.
Do stairs need a landing?
Typically, yes — the IRC generally requires landings at the top and bottom of a stairway, at least as wide as the stair and at least 36 inches deep in the direction of travel. Long straight runs may also need intermediate landings. Confirm landing rules locally before framing.
What is the difference between a tread and a riser?
The tread is the horizontal board you step on; the riser is the vertical face between treads. A flight with 5 risers has 4 treads — the top 'tread' is the upper floor or landing itself.
What lumber should I use for stair stringers?
2×12 lumber is the typical choice because the sawtooth cut removes a lot of material — you need the full 11¼-inch depth for strength. Use pressure-treated lumber for exterior stairs. Each stringer must be cut from one continuous board; never splice a stringer mid-span.
How do I measure total rise?
Measure vertically from the finished surface at the bottom (ground, patio, or lower floor) to the finished surface at the top (deck boards, upper floor). Use finished surfaces, not framing — flooring thickness changes the number.
What this calculator doesn't do
Layout math is geometry; a safe stair is code compliance. Handrail height and graspability, guard strength, headroom, nosing projection, and landing dimensions are all regulated and vary by jurisdiction — and the 3/8-inch uniformity rule means sloppy cuts can fail inspection even when the math is right. Use this page for the layout, then build to your local code (or hire a carpenter who does).
Keep estimating