Stair stringer calculator

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.

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.

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).

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

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.

The Sheet sets its code notes for the job's state or province. These are New Jersey's and Ontario's; the code reference 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.

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 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.

Stuck while you build basement or interior stairs? Ask in the Interior and basement stairs group of the StudSheet community with this Sheet attached. Homeowners who've done it and verified pros answer, and anyone can read it.

• Carpentry and framing for contractors: run this takeoff at your own prices, send the estimate, and get it signed and the deposit paid.
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• Build a storage shed (8′ × 10′ shed): A stick-built gable or lean-to shed: foundation, floor, wall framing, rafters, sheathing, siding, roofing, doors — every board counted, with the permit size limits where you live.
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• All 45 Sheets, across 16 trades.
• Code reference: frost depths, guard heights, stairs, retaining walls.