# Deck stair calculator

> Stairs for a 3′ rise: 5 risers of 7-3/16″, 4 treads and 3 stringers (2×12 × 8′), checked against the stair code. Lay out and cut stringers, treads, risers and the landing — to code.

## What to buy (Stairs for a 3′ 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 |
|---|---|---|---|
| **3 boards** | Pressure-treated 2×12 (2×12 × 8′) | 3 stringers at 17-1/4″ on center across 36″ (max 18″, DCA 6; minimum 3). Each is 4′ 6-1/2″ along the slope + 12″ for the end cuts. | Stringer stock. The deck guide (DCA 6) calls for 2×12 minimum. |
| **2 boards** | 5/4×6 treated deck board (5/4×6 × 14′) | 4 treads × 2 boards = 8 pieces at 36″. 14′ boards give 4 pieces each — the least waste. | Tread boards, 1″ thick × 5½″ wide. |
| **1 board** | Treated 1×8 (1×8 × 14′) | 4 risers at 36″. The top riser is your deck’s rim — add a board if it has no fascia. | Riser boards (7¼″ tall). |
| **3 connectors** | Adjustable stair-stringer connector (galvanized, adjustable) | One per stringer at the deck rim (DCA 6 shows connector attachment). | 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 deck screws. | Use exactly what the connector maker specifies. |
| **≈78 screws (1 box of 100)** | Coated deck screws (2½″ coated) | 2 screws per tread board at every stringer, 2 per riser board at every stringer, plus the kicker. | Exterior-rated screws for treads and risers. |
| **1 board** | Pressure-treated 2×4 (treated 2×4 × 8′) | Runs across the stringer bottoms and anchors them to the landing. | Treated against rot — for wood touching concrete or outdoors. |
| **10 bags** | Concrete mix, 80 lb (80 lb bags) | 48″ wide × 53″ deep (36″ clear in front of the bottom step + 10-3/4″ under the stringer feet + 6″) × 4″ thick = 5.89 cu ft; 80 lb bag ≈ 0.6 cu ft (Quikrete). | About 0.6 cu ft per bag. |
| **15 bags** | Base gravel (paver base) (0.5 cu ft bags) | 4″ of gravel under the pad, +20% because it compacts. | Crushed stone with fines; compacts into a firm, level base. |
| **4 boards** | 2×4 (2×4 × 8′) | Form boards around the 16′ 10″ pad perimeter. | Framing lumber, actually 1½″ × 3½″. |
| **8 stakes** | Wood stakes (12″–18″) | Two per side of the form. | Hold form boards in place. |
| **1 small box** | Concrete screws 3¼″ | 3 through the kicker into the concrete. | Anchor the bottom kicker board to the pad. |
| **1 × 8 ft + 3 brackets** | Graspable handrail + brackets (8 ft lengths + brackets) | Required with 4+ risers, on at least one side, 34–38″ above the nosings. | A rail you can wrap your hand around (1¼–2″ round). A flat 2×4 top doesn’t count. |

### In Canada (Stairs for a 914 mm 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:

- **3 boards, Pressure-treated 2×12:** 3 stringers at 438 mm on center across 914 mm (max 457 mm, DCA 6; minimum 3). Each is 1.39 m along the slope + 305 mm for the end cuts.
- **2 boards, 5/4×6 treated deck board:** 4 treads × 2 boards = 8 pieces at 914 mm. 4.27 m boards give 4 pieces each — the least waste.
- **1 board, Treated 1×8:** 4 risers at 914 mm. The top riser is your deck’s rim — add a board if it has no fascia.
- **3 connectors, Adjustable stair-stringer connector:** One per stringer at the deck rim (DCA 6 shows connector attachment).
- **1 box, Connector fasteners:** Structural screws or nails listed on the connector’s label — not deck screws.
- **≈78 screws (1 box of 100), Coated deck screws:** 2 screws per tread board at every stringer, 2 per riser board at every stringer, plus the kicker.

## The steps, in order

> **DIY OK: you can do this yourself with standard tools.** About 12–19 hours of work for this example.

1. Build the landing first (4″ gravel, 4″ concrete) and let it cure 2–3 days — you measure the rise to its top.
2. Measure the total rise from the top of the deck boards to the landing, straight down at the spot where the bottom step lands.
3. Set stair gauges on the framing square at 7-3/16″ rise and 10-1/4″ run. Mark 4 notches on the first 2×12.
4. “Drop” the stringer: cut 1″ off the bottom so the first step matches the rest once the tread is on.
5. Cut the notches with the circular saw, stopping at the lines. Finish each corner with a handsaw.
6. Test-fit the first stringer, then trace it onto the others.
7. Hang the stringers from the rim with connectors, 17-1/4″ on center; anchor the bottoms to the kicker.
8. Install riser boards, then treads: 2 boards per step, 1″ nosing overhang, ⅛–¼″ gap between boards.
9. Install a graspable handrail 34–38″ above the nosings.

## Tools (23)

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

| Tool | Need | Why |
|---|---|---|
| **Framing square** | **Must have** | Big steel L-square. With stair gauges it lays out stair stringers. |
| **Stair gauges** | **Must have** | Makes every notch identical |
| **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. |
| **Circular saw** | **Must have** | Handheld power saw for lumber and sheet goods. |
| **Handsaw** | **Must have** | Finish the notch corners — don’t over-cut with the circular saw |
| **Speed square** | **Must have** | Triangle square for marking square and angled cuts on lumber. |
| **4-ft level** | **Must have** | Checks plumb and level over a long span. |
| **Clamps (2)** | **Must have** | Hold stringers together to mark matching copies. |
| **Sawhorses** | **Must have** | Cutting support. |
| **Impact driver** | **Must have** | Drives long framing and deck screws without stripping. |
| **Cordless drill/driver** | **Must have** | Drills holes, drives screws, mixes small batches. |
| **Safety glasses** | **Must have** | Every cut, every nail, every time. |
| **Hearing protection** | **Must have** | Saws and nailers are loud enough to damage hearing. |
| **Work gloves** | **Must have** | Tack strip, block and lumber shred hands. |
| **Square shovel** | **Must have** | Cuts clean trench walls, moves gravel. |
| **Hand tamper** | **Must have** | Compacts soil and gravel in small areas. |
| **Mixing tub + hoe** | **Must have** | Mixes bagged concrete by hand. |
| **Concrete float + edger** | **Must have** | Smooths a fresh pad and rounds its edges. |
| **Wheelbarrow** | **Must have** | Moves gravel, soil and block. |
| **Hammer drill + masonry bit** | Rent | Drills the pad for the kicker’s concrete screws |
| **Miter saw** | Good to have | Clean tread and riser cuts |
| **Jigsaw** | Good to have | Cuts curves and notches. |

## Mistakes and how the math works

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

- **Forgetting to drop the stringer:** The bottom step ends up 1″ taller than the rest. Inspectors fail more than ⅜″ of variation — and people trip on it.
- **Measuring the rise at the deck edge:** Ground slopes. Measure straight down where the bottom step will actually land.
- **Over-cutting the notches:** Running the circular saw past the line cuts into the stringer’s strength. Stop short and finish by hand.

### What the calculator assumes

- IRC 2021 R311.7 / 2024 R318.7: risers ≤ 7¾″, treads ≥ 10″, ⅜″ max variation, width ≥ 36″, a 36″-deep landing top and bottom, max 151″ of rise per flight. (New Jersey’s amendments to the 2021 IRC allowed 8¼″ risers and 9″ treads; we design to the stricter IRC values.)
- Unit run 10¼″: two 5½″ boards (11¼″ tread) with a 1″ nosing (¾–1¼″ required when treads are under 11″).
- The deck surface is the top step: treads = risers − 1.
- Cut stringers: treated 2×12, at least 3, ≤ 18″ on center (DCA 6). Composite treads usually need ≤ 12″ — check your brand.
- Cut stringers span about 6 ft without mid support (DCA 6); keep ≥ 5″ of wood below the notches.
- Open risers above 30″ of total rise must stop a 4″ sphere; handrail at 4+ risers; guards where the side is > 30″ above grade.
- Landing pad: stair width + 12″, and 36″ clear in front of the bottom step plus the stringer bearing; 4″ concrete on 4″ gravel; 80 lb bag ≈ 0.6 cu ft (Quikrete). Some towns require frost-depth footings under stair stringers (NJ: 36″ in Mercer/Middlesex and north, 30″ south) — ask.

## 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 handrail is required:** Four or more risers need a graspable handrail 34–38″ above the nosings. 
- **Guards and a handrail are required:** Four or more risers need a graspable handrail 865–965 mm above the nosings. Open sides of steps more than 600 mm above the ground need a 900 mm guard with openings under 100 mm. Ontario: nothing to climb on between 140 and 900 mm above the steps — vertical balusters, no horizontal rails, cable or lattice in that zone. Confirm with your building department.
- **Permit likely needed:** A deck more than about 600 mm above the ground usually needs a building permit in Canada, and its stairs go with it — Ottawa, for example, needs one for an attached deck more than 600 mm up, or for a deck at the main entrance. This one is 0.91 m up. Confirm with your building department.
- **Frost depth:** A pad, or concrete steps with 1 or 2 risers, may sit on the ground; footings, where your municipality asks for them, go below the frost line: 1.2 m in Ontario municipal deck guides. Confirm with your building department.
- **Click Before You Dig:** Before you dig, request a free utility locate from Ontario Dig Authority (ontariodigauthority.ca) at least 5 business days ahead, and wait for the markings.

## Questions

### What materials do I need to build deck stairs?

For the worked example, a stairs for a 3′ rise, the Sheet counts 13 lines with waste included, starting with pressure-treated 2×12 (3 boards), 5/4×6 treated deck board (2 boards), treated 1×8 (1 board), adjustable stair-stringer connector (3 connectors). Each line's math is in the table above. Put in your own sizes in the [deck stairs calculator](https://app.studsheet.com/p/stairs) and every line is counted again.

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

About 12 to 19 hours for the worked example, in 9 steps. StudSheet stamps it **DIY OK**: you can do this.

### What tools do I need to build deck stairs?

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

## Ask about it

Stuck while you build deck stairs? Ask in the [Deck and porch stairs group](https://studsheet.com/forum/deck-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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