# Stair stringer calculator

> Inside stairs, 8′ 9″ rise: 14 risers of 7-1/2″, 13 treads, 4 stringers (2×12 × 16′) and 11′ 4-1/2″ of floor space. Stringers, treads, risers, skirt boards and a handrail for a straight run or one with a landing — laid out to the code’s rise, run and headroom.

## What to buy (Inside stairs, 8′ 9″ rise)

Every line shows the quantity to buy and how StudSheet got it: the spacing, the waste and the package size, so you can check it before the supply house or the quote.

| Buy | Material | How StudSheet counts it | What it is for |
|---|---|---|---|
| **4 boards** | 2×12 framing lumber (2×12 × 16′) | 4 stringers at 11-1/2″ on center across 36″ (at most 12″ under ¾″ plywood; at least 3). Each is 14′ 4-1/4″ along the slope + 12″ for the end cuts. | Actually 1½″ × 11¼″. Joists, rafters, rims and ledgers. |
| **1 board** | Pressure-treated 2×4 (treated 2×4 × 8′) | Across the stringer feet, screwed into the slab: treated, because it sits on concrete. | Treated against rot — for wood touching concrete or outdoors. |
| **4 connectors** | Adjustable stair-stringer connector (galvanized, adjustable) | One per stringer where it hangs from the header. | Galvanized bracket that ties each stringer to the deck rim. |
| **1 box** | Connector fasteners (as the connector maker specifies) | Structural screws or nails listed on the connector’s label — not drywall or deck screws. | Use exactly what the connector maker specifies. |
| **1 small box** | Concrete screws 3¼″ | 3 through the kicker into the slab. | Anchor the bottom kicker board to the pad. |
| **1 box** | 3″ framing screws | The wall-side stringers screwed into every stud they cross, 3 at each. | Construction screws for framing by hand. (16d nails if you use a nailer.) |
| **3 sheets** | Plywood ¾″, 4×8 (¾″ 4×8 sheets) | 13 treads 11-1/2″ deep (the 10-1/2″ run + 1″ of nosing) + 1 spare and 14 risers 7-1/2″ tall, ripped from 4×8 sheets: 2 pieces 36″ long from each 8′ strip. | Ripped into treads and risers for stairs that get carpet (glued and screwed to every stringer so they don’t squeak), or cut into the side forms for concrete steps. |
| **4 tubes** | Construction adhesive (10 oz tubes) | A bead on every stringer under each tread and behind each riser: about a tube per 4 treads. Glue is what keeps stairs from squeaking. | Glue bead under plates; stops squeaks and creep. |
| **≈216 screws (3 boxes of 100)** | 3″ framing screws (2½″ construction screws) | 2 per stringer through every tread and riser. | Construction screws for framing by hand. (16d nails if you use a nailer.) |
| **1 box** | Finish nails (15 or 16-ga) (15-gauge, 2″) | Skirt boards and the odd trim piece. | Face-nail the first and last rows where the flooring nailer can’t reach. Pre-drill hardwood. |
| **1 board** | Primed skirt board, 1×12 (1×12 primed × 16′) | One along each wall: the slope + 12″ for the level ends. | The finished board along the wall above the treads, cut to the stair’s slope: treads, risers and carpet butt into it. |
| **2 newels** | Box newel post (box newel) | Top and bottom of each open side, bolted into the stringer and the floor framing. | The heavy post at the ends and turns of an inside railing, fastened into the floor framing or the stringer. |
| **2 kits** | Newel mounting kit (lag or bolt kit) | One per newel: a lag or bolt kit that ties it into the framing so it can’t wobble. | A bolt or lag kit that ties the newel into the framing so it can’t wobble. |
| **26 balusters** | Wood balusters (1¼″ square or turned) (36″ and 41″, square top) | 2 per tread × 13 treads: 10-1/2″ treads leave gaps under 4⅜″. A short and a long one on each tread. | Inside balusters, set into the treads or a shoe rail and up into the handrail. |
| **1 length** | Handrail, graspable profile (graspable profile × 16′) | On top of the balusters between the newels, 36″ above the nosings: graspable, so it’s the handrail too. | The inside rail on top of the balusters. Its profile is graspable, so on stairs it is the handrail as well as the top of the guard. |
| **1 quart** | Trim & door paint (satin or semi-gloss enamel) | 14 sq ft of skirt boards × 2 coats at 350 sq ft/gal = 0.08 gal. | Semi-gloss — wipeable. |

### In Canada (Inside stairs, 2.67 m rise)

Set to Canada, the Sheet works the job out again for Ontario: metric sizes, bag sizes, the frost depth and the code notes. It doesn't just convert feet to meters. The first lines:

- **4 boards, 2×12 framing lumber:** 4 stringers at 292 mm on center across 914 mm (at most 305 mm under 19 mm plywood; at least 3). Each is 4.37 m along the slope + 305 mm for the end cuts.
- **1 board, Pressure-treated 2×4:** Across the stringer feet, screwed into the slab: treated, because it sits on concrete.
- **4 connectors, Adjustable stair-stringer connector:** One per stringer where it hangs from the header.
- **1 box, Connector fasteners:** Structural screws or nails listed on the connector’s label — not drywall or deck screws.
- **1 small box, Concrete screws 83 mm:** 3 through the kicker into the slab.
- **1 box, 76 mm framing screws:** The wall-side stringers screwed into every stud they cross, 3 at each.

## The steps, in order

> **PRO STEP: most of it is DIY-friendly; one step needs a licensed pro.** About 18–28 hours of work for this example.

1. Measure the total rise where the stairs go, finished floor to finished floor (add the flooring thickness top and bottom if it isn’t down yet).
2. Check the opening: at least 10′ 8-3/4″ long from the header back, so the nosing line stays 6′ 8″ below its edge all the way up.
3. Lay out the first stringer: stair gauges on the framing square at 7-1/2″ rise and 10-1/2″ run, 13 notches; then drop the bottom by the tread thickness (3/4″) so the first step matches.
4. Cut the notches, stopping at the lines; finish each corner with a handsaw. Test-fit, then trace the other stringers and cut the skirt boards to match.
5. Hang the stringers from the header with connectors, 11-1/2″ on center; screw the wall-side ones into the studs; kick the bottom with a treated 2×4 screwed into the slab.
6. Risers then treads: glue and screw each one, the riser first (squeak-free); keep every riser within ⅜″ of the next.
7. Handrail: 34–38″ above the nosings, returned to the wall at both ends, brackets into studs about every 4 ft.
8. Guards on the open side: newels at the top and bottom bolted into the framing, 2 balusters per tread, the handrail on top at 36″ above the nosings.
9. Paint the skirt boards: two coats of enamel over the primer.
10. Ready for carpet: sink every screw head, fill gaps over ⅛″, and sweep (the Carpet stairs Sheet counts the carpet).

## Tools (24)

Must-have tools first, then the ones that help and the ones to rent for the day.

| Tool | Need | Why |
|---|---|---|
| **Framing square** | **Must have** | Lays out every notch |
| **Stair gauges** | **Must have** | Clamp on the square so every notch is identical |
| **Circular saw** | **Must have** | Cuts the notches and rips the treads |
| **Handsaw** | **Must have** | Finishes the notch corners: don’t over-cut with the circular saw |
| **Miter saw** | **Must have** | Treads, risers and skirt boards cut square and clean |
| **Jigsaw** | Good to have | Skirt-board notches and odd cuts |
| **Tape measure (25 ft)** | **Must have** | The red boxes every 16″ on the blade are stud spacing. |
| **Carpenter's pencil** | **Must have** | Flat, doesn't roll away, marks rough lumber. |
| **4-ft level** | **Must have** | Every tread level both ways |
| **6-ft level** | **Must have** | Checks the stringers in line and the skirt boards straight |
| **Chalk line** | Good to have | Snaps the stringer line on the wall |
| **Clamps (2)** | **Must have** | Hold stringers together to mark matching copies. |
| **Sawhorses** | **Must have** | Cutting support. |
| **Cordless drill/driver** | **Must have** | Drills holes, drives screws, mixes small batches. |
| **Impact driver** | **Must have** | Drives the stringer and tread screws |
| **Caulk gun** | **Must have** | Construction adhesive under every tread |
| **Stud finder** | **Must have** | Finds the studs for the stringers and the handrail brackets |
| **Finish nailer (15/16-ga)** | Good to have | Skirts and risers, fast and with small holes |
| **Hammer drill + masonry bit** | Rent | Drills the slab for the kicker’s concrete screws |
| **Safety glasses** | **Must have** | Every cut, every nail, every time. |
| **Hearing protection** | **Must have** | Saws and nailers are loud enough to damage hearing. |
| **N95 dust masks** | **Must have** | Sawdust, and sanding the finish between coats |
| **Work gloves** | **Must have** | Tack strip, block and lumber shred hands. |
| **Step ladder (6 ft)** | **Must have** | For the header and the top of the handrail |

## Mistakes and how the math works

### Mistakes that cost a callback or a second trip

- **Measuring the rise before the finish floors:** New flooring at the top or bottom makes the first or last step taller or shorter than the rest — measure finished floor to finished floor.
- **Forgetting to drop the stringer:** The bottom step ends up 3/4″ taller than the rest. Inspectors fail more than ⅜″ between steps, and people trip on it.
- **Headroom checked only at the top step:** The tightest spot is under the opening’s edge: measure 6′ 8″ straight up from the nosing line there.
- **Nails only:** Treads and risers glued and screwed don’t squeak; nailed ones do within a year.
- **A handrail that just stops:** Return each end to the wall or a newel so a sleeve or a bag strap can’t catch on it.

### What the calculator assumes

- IRC 2021 R311.7 / 2024 R318.7: risers ≤ 7¾″, treads ≥ 10″ (nosing ¾–1¼″ when the tread is under 11″), ⅜″ max variation, width ≥ 36″, headroom 6′ 8″ along the nosing line, at most 12′ 7″ (151″) per flight, handrail 34–38″ at 4+ risers; guards over a 30″ drop (R312; R321 in the 2024 IRC).
- Layout: 14 risers of 7-1/2″ (from 7-1/2″ preferred) and 13 treads of 10-1/2″ run + 1″ of nosing; the upper floor is the top step. 2R + T = 25.5″ (24–25″ is comfortable).
- Stringers: 2×12, cut, at most 12″ apart under ¾″ plywood treads (typical), at least 3, hung from the header with connectors; at least 3½″ of wood left below the notches.
- Headroom: 6′ 8″ measured straight up from the line along the nosings to the underside of the floor above (the floor 11-1/4″ thick at the opening), so the opening runs back from the header at least 10′ 8-3/4″.
- Pull-down attic ladders aren’t counted here; a fixed stair to an attic needs a full-size opening, which is structural work.

## Code, permits and safety

The Sheet sets its code notes for the job's state or province. These are New Jersey's and Ontario's; the [code reference](https://studsheet.com/codes) has more. Always confirm with your building department.

- **A guard on the open side:** The open side is more than 30″ above the floor, so it needs a guard at least 34″ tall (measured from the nosings) with openings under 4⅜″ (IRC R312.1; R321.1 in the 2024 IRC): 2 balusters per tread, a newel at the top and the bottom bolted into the framing, and the handrail on top. Solid newels are the hard part; the Railings Sheet lays out other styles.
- **A handrail is required:** Stairs with 4 or more risers need a graspable handrail 34–38″ above the nosings on at least one side (IRC R311.7.8; R320 in the 2024 IRC). It runs the whole flight, ends returned to the wall or a newel, 1½″ from the wall.
- **Permit likely needed:** A new or replaced stair is structural work: New Jersey towns usually want a construction permit, with a framing inspection. Ask your town’s construction office.

## Questions

### What materials do I need to build basement or interior stairs?

For the worked example, a inside stairs, 8′ 9″ rise, the Sheet counts 16 lines with waste included, starting with 2×12 framing lumber (4 boards), pressure-treated 2×4 (1 board), adjustable stair-stringer connector (4 connectors), connector fasteners (1 box). Each line's math is in the table above. Put in your own sizes in the [inside stairs calculator](https://app.studsheet.com/p/istairs) and every line is counted again.

### How long does it take to build basement or interior stairs, and can I do it myself?

About 18 to 28 hours for the worked example, in 10 steps. StudSheet stamps it **PRO STEP**: dIY with a pro for one step.

### What tools do I need to build basement or interior stairs?

24 in all. The must-haves start with framing square, stair gauges, circular saw, handsaw, miter saw, tape measure (25 ft). On the Sheet you mark each one as owned, to buy or to rent.

## Ask about it

Stuck while you build basement or interior stairs? Ask in the [Interior and basement stairs group](https://studsheet.com/forum/interior-stairs) of the StudSheet community with this Sheet attached. Homeowners who've done it and verified pros answer, and anyone can read it.

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