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Stairs are one of the few builds where you can't just follow a cut list off the page, because the right dimensions depend entirely on the height you're covering. This plan teaches the calculation instead of a fixed set of numbers: divide your total rise by about 7" to get a whole number of steps, divide the total rise by that whole number to get the height of each step, then pick a tread depth you're happy with. The worked example here — a 16" total rise split into two 8" steps — is there to show the method, not because your stairs will be 16" tall.
Once the math is done, the actual building is repetitive: mark one stringer with a square set to your rise and run, cut it, then use it as a template to mark the rest. A rafter square with adjustable stops turns this from careful measuring into just lining the square up with your last mark and tracing — that's what makes "stair math" fast once you've done it once. Cut the inside corners of each notch with a hand saw after the circular saw does the two straight cuts; a circular saw blade is round and will overcut past the corner if you try to finish the notch with it alone.
| Item | Qty |
|---|---|
| 2x12 board, 8 ftStringers. Use 2x10 or 2x8 instead if your rise/run cuts leave enough solid wood below the notches — 2x12 gives the most margin. | 2 each |
| 2x6 board, 8 ftOne board for the ledger/back board, two for tread boards (two boards per tread, side by side, gives an 11" tread depth with a little nosing). | 3 each |
| Deck screws, 3" | 30 each |
Overall cost: $$. Lumber prices vary by region, species, and season, so we give a band rather than a figure we would only be pretending to know.
| Part | Qty | T × W × L |
|---|---|---|
| Stringers2x12Length is generous stock to notch from — mark and cut your rise/run pattern per your own calculated numbers, not this length directly. | 2 | 1 1/2" × 11 1/4" × 30" |
| Ledger / back board2x6Set stair width to 36" here; adjust to your own opening. | 1 | 1 1/2" × 5 1/2" × 36" |
| Tread boards2x6Two boards per tread for a two-step run, laid side by side with a small gap. | 4 | 1 1/2" × 5 1/2" × 36" |
Buy 4 boards at 8 ft.
1 board
3 boards
Assumes 8 ft stock, a 1/8" saw kerf, and buying each part at its own width. Change the board size or kerf on the full board plan →
Measure the overall height your stairs need to cover and the width you want them. Divide the overall height by about 7 and drop the decimal — that whole number is how many steps (rises) you need. Divide the overall height by that number of rises to get the exact height of each step.
Then decide your tread depth. If it doesn't matter exactly where the stairs land, two 2x6 boards side by side gives about an 11" tread with a little nosing — an easy, comfortable default. If your stairs must land at a specific spot, divide your total available run by the number of treads instead.
Set your speed square (or rafter square) to your calculated rise and run measurements. Line the square up with the edge of the stringer board and trace the rise/run notch. This first stringer is your template for every following one, so take the time to get it right.
Slide the square down the board, lining it up with your previous mark and the board's edge, and trace the next notch. Repeat for every step, then cut both stringers with a circular saw for the straight runs and a hand saw to finish each inside corner cleanly.
Screw the ledger/back board to the tops of both stringers, then attach that assembly to your landing or deck framing, checking it's level and that both stringers are plumb and evenly spaced for your stair width.
Starting at the bottom, screw down the first tread's two boards to the stringer notches, using a pencil laid on its side as a quick, repeatable gap spacer between the boards. Work your way up, checking each tread stays level, and screw every tread down securely.
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