Stair Calculator

Enter your floor-to-floor height. Get risers, treads, step dimensions, and stringer length instantly.

Also flags basic IRC code checks (max rise, min run, 2R + R comfort) — verify anything critical with your local building department.

Rise: — vertical height of one step
Stringer: — diagonal structural support
Run: — horizontal depth of one tread
Tread: — walking surface
Nosing: — overhang past riser below

For quick planning and sanity checks — always verify with your local building code before cutting stringers.

Stair anatomy — left-column callouts identify each structural part via horizontal leaders to the feature. Dimensions show total rise, stringer height, total run, stringer length (L = √(R² + T²)), and the stair angle. Hover or tap any callout to highlight its definition in the glossary below.

Calculate Your Stairs

Start from a preset:

Click any preset to fill the form and recalculate. Each field keeps its own unit — change any row's unit independently.

Total rise · typical: 8–10 ft (96–120 in)

9 ft floor = 108 in. Measure floor-to-floor including finished surfaces.

Rise · typical: 7 in (comfortable), max: 7¾ in (IRC)

How do you want to enter the run?

Per-step: enter each tread's run (typical 10–11"). Total: enter the full horizontal span your stairs need — we'll split it across the treads.

Run · typical: 10–11 in, min: 10 in (IRC)

Your Stairs

Number of risers: 15
Number of treads: 14
Rise: 7.2" 18.3 cm
Total run: 12' 10" 391.2 cm
Stringer length: 15' 4-1/16" 467.5 cm
2×Rise + Run: 25.4"

Alternate configurations

For your inputs, these tread counts are all valid. The recommended pick passes every IRC check and sits closest to the 2R+R ergonomic target (~25"). Click a neighbour to try it.

The IRC checks shown here cover dimensional rise/run minimums only. They don't certify the full design — local amendments, structural detailing, and install quality also determine code compliance. Confirm with your local building department before construction.

Show all valid configurations

Treads	Rise	Run	2R+R	IRC check

✓ Passes IRC dimensional checks (R311.7.5)

This compares your dimensional inputs against IRC 2021 minimums only. It does not certify the full design — local amendments, structural detailing, and install quality also determine code compliance. Confirm with your local building department before construction.

What was checked · 3 IRC provisions

Rise within IRC maximum — actual 7.2", standard ≤ 7.75" IRC §R311.7.5.1 ↗
Rise above IRC minimum — actual 7.2", standard ≥ 4" IRC §R311.7.5.1 ↗
Run meets IRC minimum — actual 11", standard ≥ 10" IRC §R311.7.5.2 ↗

Not checked by this calculator · 8 other IRC provisions

This calculator verifies dimensional rise/run only. The following IRC requirements must be verified separately with your local building authority:

Stair width (≥ 36") · IRC §R311.7.1
Headroom clearance (≥ 6'8") · IRC §R311.7.2
Handrail height (34–38") and graspability · IRC §R311.7.8
Rise variation within a flight (≤ 3/8") · IRC §R311.7.5.1
Nosing projection (3/4"–1 1/4") · IRC §R311.7.5.3
Landing required every 12' of rise · IRC §R311.7.6
Guardrail + baluster spacing · IRC §R312
Local jurisdiction amendments to IRC · IRC §(varies)

Based on International Residential Code (IRC) 2021. Local jurisdictions may adopt different editions or add amendments — always confirm with your local building department before construction.

Build notes — first-step cut adjustment

1st step cut depth (bottom stringer): 5.95" 15.1 cm
1st step walking surface (with tread): 7.2" 18.3 cm

Cut the bottom stringer shorter than the others by exactly the tread thickness (1.25"). When you lay the bottom tread on top of that cut, the finished first step matches every other step — no tripping hazard. (Standard mount only; for flush-mount this adjustment is not needed.)

📋 Your Build List

78 items ready to buy — quantities update as you change inputs above.

🛒 Build cart at Home Depot →

Estimate only — not a professional bill of materials. Verify every quantity against your actual cut list, site conditions, and local building authority before purchasing. This list is not engineering, architectural, or contracting advice. See our full disclaimer for details.

Affiliate disclosure: CraftedCalcs earns commission on purchases made through the links below. We only recommend items we'd use ourselves and that fit the stair you just calculated. The commission doesn't change your price.

3 Pressure-treated 2×12 stringer 16' PT lumber Home Depot
14 Oak stair tread 11" × 42" Home Depot
14 1×8 riser board Primed pine, 42" cut-to-fit Home Depot
42 Simpson LSC stair connector Galvanized steel, pre-bent Home Depot
1 Box of 3" structural screws ~100 count per box Home Depot

Click each item to see its current price at Home Depot. Quantities assume a single flight with the dimensions shown above; adjust if your project has landings, turns, or exposed sides.

The Math

Number of risers = round(total_rise ÷ target_rise)
rise = total_rise ÷ number_of_risers
number_of_treads = number_of_risers − 1
total_run = number_of_treads × run
Ergonomic check: 2 × rise + run should be 24–26"

Stringer geometry branches by mount type:

Standard mount (deck is top tread, risers = treads + 1):
  stringer_span   = total_rise − rise
  stringer_length = √(stringer_span² + total_run²)
  stair_angle     = atan(rise ÷ run)

Flush mount (top tread flush with deck, risers = treads):
  stringer_span   = total_rise
  stringer_length = √(total_rise² + total_run²)
  stair_angle     = atan(total_rise ÷ total_run)

The stringer (the diagonal support board) follows the Pythagorean theorem — but WHICH triangle depends on how the stringer attaches. In standard mount the deck surface itself acts as the top tread, so the physical stringer board spans from the lower floor to the second-to-last tread (total rise minus one rise). In flush mount the stringer top is level with the deck, so it spans the full total rise. Both mounts are common in residential construction and the choice affects lumber length + angle. The 2R+R ergonomic rule has been used since Nicolas-François Blondel documented it in 1672; it matches the natural gait of human walking.

Source: IRC R311.7.5 + standard residential carpentry practice

How This Calculator Works

Three numbers drive every staircase: total rise (how tall — from finished floor to finished floor), rise (vertical height of one step), and run (horizontal depth of one tread). Get these right, and everything else — number of steps, stringer length, landing position — falls out of the math.

The calculator rounds the number of risers to the nearest whole number, then recalculates the actual rise per step so every step in the flight is equal. This is required by code: the tallest and shortest riser in a flight can't differ by more than 3/8 inch. A flight with uneven steps is a trip hazard and a code violation.

Inputs explained

Total rise: measure from the finished floor at the bottom to the finished floor at the top. Include carpet, tile, or hardwood thickness. Common residential values: 96 (8 ft), 108 (9 ft), 120 (10 ft).
Rise: the per-step vertical. 7 inches is the comfort standard. The IRC maximum is 7¾"; stairs designed right at the max often feel steep.
Run: the per-step horizontal (a.k.a. tread depth in IRC language). 10 inches is the IRC minimum. 11 inches is common for residential; commercial + public stairs often run 12 inches.

What the outputs mean

Stringer length is the diagonal — order your stringer lumber at this length plus a few inches for attachment. A standard 16-foot 2x12 covers most 9-foot residential stairs. 2×Rise + Run is the ergonomic check; if this number falls outside 24–26 inches, the stairs may feel awkward even if code-compliant.

Standard mount vs. flush mount — and why it changes the stringer math

Under the hood there are two physical ways a stringer attaches at the top, and the formulas differ between them. Toggle the mount type in Advanced mode if your build uses flush mount.

Standard mount (default): the deck or upper-floor surface itself is the top tread. The stringer board spans from the lower floor up to the second-to-last tread and hangs beneath the upper-floor framing via a joist-hanger connector. Stringer board height = total rise − one rise. This is the common residential convention and matches how most carpenters cut a 2x12 against a framing square.
Flush mount: the top of the stringer is cut level with the upper-floor surface; the first tread board then sits on top of the stringer at deck height. The stringer spans the full total rise. Flush mount adds one extra tread of horizontal footprint and is often chosen when ground-slope or appearance allows.

Our formulas branch automatically on the mount type you pick. The stringer length we report is the minimum length of 2x12 you need for the physical board itself — order a bit longer to allow for cuts and attachment flats. The stair angle we report is the actual slope of the stringer board, which in standard mount equals the per-step slope atan(rise ÷ run) and in flush mount is the overall diagonal atan(total rise ÷ total run).

Same total rise, same slope — only the stringer board differs. In standard mount the stringer is cut one rise shorter and the deck itself is the top tread. In flush mount the stringer spans the full floor-to-floor height and its top tread sits level with the deck. CraftedCalcs branches the stringer length, stringer height, and angle formulas automatically based on the mount type you select.

Formula convention follows standard residential carpentry practice and IRC §R311.7.5 ↗ . Pythagorean geometry traces to classical trigonometry; Blondel's 2R+R ergonomic rule dates to 1672.

Common Mistakes

The seven errors that most often cause failed inspections or awkward stairs.

Measuring finished vs subfloor: if you measure before flooring goes in, the actual rise increases when tile or hardwood is laid. Always measure with the final floor thickness included — or add it to your total rise before calculating.
Uneven top or bottom riser: the top riser's height is affected by floor thickness above; the bottom is affected by what you land on (tile, concrete slab). IRC requires variation ≤ 3/8" across the flight. Plan for these differences or adjust your cut accordingly.
Forgetting the nosing: if treads have a 1" nose overhang, the visible run is smaller than (number of treads × run). Include the nose projection in your run number or subtract it from the total run before cutting the stringer.
Ignoring proportion and scale: a perfectly code-compliant stair can still feel steep or awkward. Use the 7-11 rule (2 × rise + run ≈ 25") as the ergonomic target even when code allows more aggressive ratios.
Overlooking light and visibility: stairs tucked into dim corners become trip hazards. Plan for a switch at top AND bottom, and consider a natural-light source if routing allows. IRC requires a light switch at each end of a stair with 6+ risers.
Choosing style over practicality: open-riser stairs, floating designs, and ultra-thin treads look modern but fail code in many jurisdictions (e.g., baluster spacing and maximum 4" spheres). Verify visual choices against IRC §R311.7 + IRC §R312 before buying materials.
Inadequate safety hardware: handrail is required for any flight of 4+ risers ( IRC §R311.7.8 ). Guardrails with < 4" baluster spacing are required wherever the stair edge is 30"+ above grade. Budget for these upfront — retrofitting is expensive.

What Else You'll Need

Calculator output covers the headline material. This list is the full bill — the fasteners, brackets, sealants, and safety hardware beginners typically forget to buy on the first trip.

Structural

Stringers Home Depot

Qty: 2 stringers for widths ≤ 36"; 3 for wider · 2×12 pressure-treated (exterior) or straight-grain 2×12 (interior). Order length = stringer length × 1.05 to allow waste.
Stringer top brackets Home Depot

Qty: 1 per stringer · Simpson LSC or equivalent joist hanger — secures stringer to top header.
Tread material Home Depot

Qty: 14 treads (example run) · 5/4 deck boards OR solid 1"–1¼" hardwood (oak, maple) for interior.
Riser boards · optional Home Depot

Qty: 15 risers (example run) · ½" or ⅝" paint-grade for closed-riser stairs. Skip for open stairs.

Fasteners

Tread screws Home Depot

Qty: ~4 per tread per stringer · 2½" or 3" deck screws (exterior) or #10×2½" wood screws (interior). Pre-drill to prevent splits.
Riser nails/screws · optional Home Depot

Qty: ~6 per riser · Finish nails or 2" trim-head screws. Only if using risers.
Construction adhesive · optional Home Depot

Qty: 1 tube per 4–5 treads · Liquid Nails or PL Premium on tread-to-stringer contact — prevents squeaks.
Hanger nails or SD screws Home Depot

Qty: Per bracket spec · 1½" Simpson SD screws for LSC brackets (galvanized for exterior).

Safety + Code

Handrail Home Depot

Qty: Length of stringer × 1.1 · 1½"–2" round (IRC §R311.7.8 ↗ graspable). Continuous top-to-bottom for any flight of 4+ risers.
Handrail brackets Home Depot

Qty: Every ~48" of run + 1 at top + 1 at bottom · Rated 200 lb minimum. Metal or powder-coated.
Guardrail + balusters · optional Home Depot

Required if stair is > 30" above grade (IRC §R312 ↗). 36" residential height, balusters spaced < 4" apart.
Non-slip nosing treatment · optional Home Depot

Adhesive strips or rubber inserts for exterior/high-traffic stairs.

Finish

Stain or sealant for treads Home Depot

Exterior: penetrating oil (Cabot, Ready Seal). Interior: 2–3 coats oil-based poly.
Stain for risers + stringer sides · optional Home Depot

Paint-grade primer + 2 coats latex for closed-riser paint finish.
Carpet or tread pads · optional Home Depot

If finishing over bare wood — order 10% more than tread count for stair carpet pattern match.

Affiliate disclosure: CraftedCalcs earns commission on purchases made through the Home Depot links above. We only recommend items we'd use ourselves. The commission doesn't change your price.

15 items across 4 categories. Quantities assume standard residential practice — adjust up for longer spans, complex geometry, or pro-grade specification.

Stair Terminology

14 terms — every one is a standard stair-code definition or a calculator input. Expand to browse.

Rise: The vertical height of one step — from the top of one tread to the top of the next. Every riser in a flight must be equal (within 3/8").; IRC §R311.7.5.1 ↗ · Max 7¾" for residential; min 4".
Run: The horizontal depth of a single tread — not including the nosing overhang. Sometimes called "going" or "tread depth".; IRC §R311.7.5.2 ↗ · Minimum 10" in residential construction.
Total Rise: The full vertical distance from the finished floor at the bottom of the stairs to the finished floor at the top. Measure with finished surfaces (tile, hardwood) in place — or add their thickness.
Total Run: The full horizontal distance the stairs span — equal to (number of treads) × (run per tread). Determines how much floor space the staircase occupies.
Tread: The horizontal surface of each step — the part you walk on. Typically cut from 2× dimensional lumber or prefabricated stair treads, often 1" or 1 1/4" thick.; IRC §R311.7.5.2 ↗ · Tread depth and surface requirements are specified alongside run.
Nosing: The rounded or squared edge of a tread that projects beyond the riser below. Improves footing and visual alignment.; IRC §R311.7.5.3 ↗ · Allowed projection: ¾" to 1 1/4".
Stringer: The diagonal structural board that supports the treads and risers — runs from the top floor to the bottom. Residential stairs typically use 2×12 pressure-treated (exterior) or straight-grain 2×12 (interior). Stringer length follows the Pythagorean theorem: √(totalRise² + totalRun²).; IRC §R311.7.5 ↗ · The IRC specifies tread + riser requirements that together govern stringer cut geometry.
Headroom: The vertical clearance above the stairs — measured from the nosing line (imaginary diagonal through each nosing) to the lowest obstruction above (ceiling, beam, floor joist).; IRC §R311.7.2 ↗ · Minimum 6'8" (80") above the nosing line. A common reason for failed inspections.
Stair Width: The clear horizontal width between handrails (if any), measured at their narrowest point. Important for moving furniture and emergency egress.; IRC §R311.7.1 ↗ · Minimum 36" clear width for residential stairs.
Handrail: The graspable rail running alongside the stairs for support. Must be continuous from top to bottom of any flight with 4+ risers.; IRC §R311.7.8 ↗ · Height 34–38" above nosings; graspable diameter 1¼" to 2" (round) or equivalent.
Guardrail: The protective barrier — usually with balusters — wherever the stair or its landing is more than 30" above the surface below. Prevents falls off the side.; IRC §R312 ↗ · Height 36" residential, 42" commercial. Baluster gaps < 4".
Landing: A flat platform interrupting a stair run — required at the top and bottom, and every 12' of vertical rise for long flights. Also required where stairs change direction.; IRC §R311.7.6 ↗ · Minimum 36" in the direction of travel; matches the stair width otherwise.
Winder: A tapered tread in a stair that changes direction without a flat landing — the narrow end of the tread is at the inside of the turn. Code limits the narrow-end width.; Narrow end minimum 6"; at 12" from the narrow end, tread must be at least 10" deep.
Mount Type: How the top of the stringer meets the upper floor: "standard" (stringer bolts to the face of the top floor framing, top tread flush with the floor) or "flush" (stringer cut so the top tread IS the top floor — eliminates a last step).; Affects step count and top-riser height — gets this wrong and your top step is uneven.

Frequently Asked Questions

How do I calculate how many stairs I need?

Divide your total rise (floor-to-floor height in inches) by the rise you want per step (typically 7 inches for comfortable stairs). Round to the nearest whole number. That's your number of risers. The number of treads is always one less than the number of risers, because the top floor acts as the final tread.

For a 108" (9 ft) total rise: 108 ÷ 7 = 15.4, rounded to 15 risers. That gives you 14 treads and a comfortable 7.2" step.

What is the 7-11 rule for stairs?

The 7-11 rule sets stair proportions by pairing a 7-inch riser with an 11-inch tread. This ratio (also expressible as "2 × rise + run ≈ 25") produces a walking rhythm that matches the natural human gait — climbing feels steady rather than steep, and descending feels secure rather than cramped. A 7" rise with an 11" run gives 2(7) + 11 = 25, landing squarely in the ergonomic sweet spot of 24-26 inches.

The rule is not in the IRC as a hard requirement, but it underlies why IRC §R311.7.5.2 ↗ mandates minimum 10" treads and IRC §R311.7.5.1 ↗ caps risers at 7¾". Stairs that deviate — say, 8" rise with 9" run (2(8)+9=25, same "math" but much steeper) — feel awkward despite the arithmetic. Keep rise at 7" and run at 11" whenever layout allows; it's why it became a rule.

What is the standard rise and run for stairs?

Per the International Residential Code (IRC §R311.7.5 ↗): maximum rise is 7¾ inches, minimum is 4 inches. Minimum run (tread depth) is 10 inches. The ergonomic "rule of 25": 2 × rise + run should equal 24–25 inches for comfortable walking. A 7" rise with an 11" run gives 2(7) + 11 = 25 — the sweet spot.

How do you calculate stringer length?

Use the Pythagorean theorem: stringer length = √(total rise² + total run²). For a 108" rise and 154" total run: √(108² + 154²) = √(11,664 + 23,716) = √35,380 ≈ 188.1 inches, or roughly 15 feet 8 inches. Add a few inches for attachment at top and bottom — most carpenters round up and trim.

What is the maximum rise allowed by code?

The IRC (IRC §R311.7.5.1 ↗) sets the maximum rise at 7¾ inches for residential stairs. Commercial stairs are typically limited to 7 inches max. Exceeding the max rise is both a code violation AND a trip hazard — your stairs should be rejected during inspection if any rise exceeds 7¾ inches. Variation between steps must be under 3/8 inch (the largest and smallest riser can differ by no more than that).

Do I need a handrail on stairs?

The IRC (IRC §R311.7.8 ↗) requires a handrail on any stairway with four or more risers. The handrail must be 34–38 inches above the nosing, be graspable (1¼–2 inches in diameter for round), and run continuously from top to bottom. A guardrail (IRC §R312 ↗; 36" residential, 42" commercial) is required wherever the floor level is 30" or more above the surface below.

How much does a stair stringer weigh?

A typical 2x12 pressure-treated pine stringer for a 9-foot staircase (about 16 feet in length) weighs approximately 45–55 pounds. Most residential stairs use 2 or 3 stringers — middle stringer recommended if treads span more than 36 inches. LVL (laminated veneer lumber) stringers are lighter and straighter but more expensive.

Can I DIY stair construction?

For interior or deck stairs up to a standard 9-foot rise, yes — with care. The math here gets you the design; the build requires accurate cutting, level installation, and attention to building code. For commercial stairs, stairs with landings + turns, curved/spiral stairs, or any load-bearing structural element, hire a licensed contractor. When in doubt, consult your local building inspector before starting — rejection after construction is expensive.