Measuring before you order lumber
This calculator turns one measurement — total rise — into a full cut list. Get that number right and the species, stringer count and board feet all follow correctly.
Find your total rise
Hold a tape measure or a straight board plumb from the finished floor you're leaving to the finished floor you're arriving at. On an existing opening, drop a plumb bob from the top nosing line to the finished floor below.
Set your clear stair width
Measure wall-to-wall (or the finished width you're building to) — this decides how many stringers you need and how wide each tread and riser board has to be cut.
Pick closed or open risers, and your species
Closed risers add a full board per step to the list; open risers drop that line item entirely. Species and grade change which spans and treated-lumber flags apply below.
Read the compliance chips, then order with the waste factor applied
Green means the geometry sits inside IRC residential limits. The board feet total already the raw cut list — the "Purchase" figure adds your waste factor on top so you don't come up short at the job site.
The six formulas behind every result
Nothing on this page is a black box. Here's exactly what runs when you change a number, from step geometry through to the board feet you order.
Step Count & Riser
Total rise divided by your target riser, rounded to a whole step count, then re-divided for the exact riser you actually cut.
Tread Depth (2R+T rule)
Standard comfort formula, floored at the 10" IRC minimum tread depth.
Stringer Length
The straight-line hypotenuse of the stair triangle — the raw cut length before birdsmouth and notch allowance.
Stringer Board Length
Adds allowance for the birdsmouth cut and notch waste, then rounds up to a standard stocked lumber length.
Board Feet
The standard board-foot formula, using nominal thickness and width in inches. A 16' 2×12 = (2 × 12 × 16) ÷ 12 = 32 BF.
Purchase Quantity
Raw cut-list board feet inflated by your waste factor, rounded up to the next whole board foot before you order.
Walking through a real 108" rise, 36" wide
Same geometry as this site's Stair Rise and Run Calculator (a 9-foot basement stair), carried through to a full lumber list — the default this calculator loads with.
Geometry: steps, riser, tread, stringer
108" rise ÷ 7.5" target = 14.4, rounds to 14 steps. Re-dividing gives a 7.71" actual riser. The 2R+T rule wants a 9.57" tread, which is below the 10" IRC minimum, so it floors at 10". Total run for 13 treads is 130", and the stringer hypotenuse is √(108² + 130²) ≈ 169.0".
Stringer count and board length
At 36" clear width using the ~18" spacing rule of thumb: 36 ÷ 18 = 2, +1 = 3 stringers. Each needs 169" plus roughly 14" for the birdsmouth and notch waste = 183", which rounds up to the next stocked length: a 16-foot (192") 2×12.
Board feet
One 16' 2×12 = (2 × 12 × 16) ÷ 12 = 32 board feet. Three stringers = 96 BF raw. This is the number that scales directly with species price — swapping SPF for pressure-treated SYP changes cost per board foot, not the board-foot count itself.
Treads, risers, fasteners & purchase quantity
Closed risers add one board per tread and one per riser: 13 tread boards, 14 riser boards (one per step, including the top riser). With stair-tread hangers at one per stringer-to-tread connection, that's 3 stringers × 13 treads = 39 hangers. Applying a 10% waste factor to the 96 BF of stringer stock: 96 × 1.10 = 106 board feet to purchase.
The tread and riser board counts above assume one length of stock per piece — for exact finish-grade footage and cut optimization across standard board lengths, use the dedicated Tread and Riser Material Calculator linked below.
Choosing stringer species and grade
All four options below are commonly stocked for stair stringers. The right one depends on span, exposure, and budget — not just what's cheapest per board foot.
| Species & Grade | Typical Use | Relative Strength | Treated? |
|---|---|---|---|
| SPF #2 | Interior stairs, standard spans | Baseline | No |
| Douglas Fir-Larch #2 | Interior or covered exterior, longer spans | Higher than SPF [VERIFY locally] | No |
| Southern Yellow Pine #2 | Interior or covered exterior, longer spans | Higher than SPF [VERIFY locally] | No |
| SYP #2 Pressure-Treated | Exterior, ground-adjacent, deck stairs | Same as untreated SYP | Yes |
Relative strength ranking is a general framing convention, not a substitute for a species/grade-specific span table (e.g. IRC/AWC span tables). Confirm allowable span for your exact grade stamp before ordering, especially for stringers spanning further than roughly 6 feet unsupported.
IRC residential stair code, quick reference
This calculator checks your geometry against the two limits below. Stringer spacing, fastener schedules and treated-lumber requirements vary more by jurisdiction — treat those figures as planning estimates.
| Element | Residential (IRC) | Commercial (IBC) |
|---|---|---|
| Max riser height | 7.75" | 7" |
| Min tread depth | 10" | 11" |
| Riser variance across a flight | 3/8" | 3/8" |
| Min clear width | 36" | 44"+ (varies) |
| Stringer spacing (planning rule of thumb) | ≈16–18" o.c. [VERIFY] | Engineered per span table |
| Wood in contact with concrete/soil | Pressure-treated or naturally durable species required | Same |
Reference only — always confirm against your local jurisdiction's adopted code before building. The stringer spacing row is flagged because allowable spacing depends on tread material and load, not on geometry alone; see the Stringer Spacing Calculator linked below for an engineered figure.
Stringers, fasteners & board feet
Geometry gives you the shape. This section covers how that shape turns into a stringer count, a fastener count, and a number of board feet you actually order.
How many stringers
A commonly cited planning rule of thumb for stringer spacing [VERIFY]. A standard 36" wide stair lands on 3; wider stairs, or ones getting a heavy finish like tile or stone, typically need a 4th. Actual maximum spacing depends on tread material and load — see the Stringer Spacing Calculator for an engineered figure.
Board length per stringer
The straight-line stringer length is the hypotenuse only. Add roughly 14" for the birdsmouth cut at the top and notch waste, then round up to a stocked lumber length — 8', 10', 12', 14', 16', 18' or 20'.
Tread & riser board count
One board per tread, one per riser including the top riser at the upper floor line. Open-riser stairs drop the riser board line entirely, which this calculator reflects when Open is selected.
Fastener count
One connection point per stringer, per tread [VERIFY]. Stair-tread hangers count one per connection; structural screws are commonly specified two or more per connection — always follow the fastener manufacturer's load rating and spacing.
These are planning-stage material estimates, not a stamped structural design. A wide stair, an unusual load, treated-lumber fastener corrosion requirements, or a long single stringer span may need an engineer's sign-off regardless of what this calculator shows.
Common mistakes when ordering wood stair lumber
Most job-site material shortages trace back to one of these five planning errors, not to bad carpentry.
Ordering the raw cut length, not the stocked length
A 169" calculated stringer isn't a lumber-yard length. Always order the rounded-up stocked length (here, 16') — the raw hypotenuse will come up short once the birdsmouth and notch cuts are made.
Skipping the waste factor
Culled boards, miscuts, and defects are normal on a stringer run with notched cuts. Ordering exactly the raw board feet — with no cushion — is a common reason a crew is short a board mid-install.
Using untreated lumber where it contacts concrete or soil
Stringers landing on a concrete slab, or any stair framing in ground contact, needs pressure-treated or naturally durable lumber — code requirement, not a preference, in most jurisdictions.
Forgetting the top riser board on closed-riser stairs
The riser count equals the step count, not the tread count — one more riser board than tread boards. Ordering by tread count alone leaves the top riser uncut.
Guessing at fastener count instead of following the hanger spec
Stair-tread hanger and structural screw counts here are planning estimates. The manufacturer's load rating and spacing table — not a rule of thumb — determines the actual fastener schedule for a code-compliant connection.
When to use a wood stair calculator
This tool earns its keep specifically when you need a lumber list, not just a riser and tread number.
Material Take-Off & Ordering
Generating a board feet count before a lumber yard run or delivery order.
Bid & Estimate Prep
Pricing stringer, tread and riser stock by species before quoting a job.
Deck & Exterior Stair Builds
Sizing pressure-treated stringer stock for ground-adjacent or exterior stairs.
Home Renovation
Replacing a worn staircase and needing a full replacement cut list, not just dimensions.
New Construction Framing
Ordering stair-framing lumber ahead of the rough framing package.
DIY Planning & Budgeting
Understanding roughly how much lumber, and what grade, a project needs before committing.