What are stair risers?

The vertical board between two horizontal stair treads. Closed risers (most common) are solid 1×8 PT boards. Open risers leave the gap open between treads (modern aesthetic). IRC R311.7.5.1 requires risers to be ≤ 7.75″ tall + open-riser gaps ≤ 4″ sphere — open risers are usually NOT residential-compliant.

How many risers does a 5-step stair have?

5 risers — same as step count. Each riser is the vertical face between two treads. The bottom riser sits on grade, the top riser meets the deck edge. Risers can be cut from 1×8 stock for typical 7.25″ riser height (1×8 actual is 7.25″, perfect fit).

Are open risers code-compliant?

Rarely for residential. IRC R311.7.5.1 requires open-riser openings to be small enough that a 4″ sphere CANNOT pass. For a typical 7″ riser with 1″ tread thickness, the opening is 6″ — too big. Open risers ONLY work IRC-compliantly on very low decks (≤ 5″ riser height = ≤ 4″ opening). Most modern 'open riser' designs you see require a permit variance OR they're commercial stairs (different rules).

What size lumber for stair risers?

1×8 PT pine (7.25″ actual) for the standard 7-7.5″ riser height. 1×6 PT (5.5″ actual) for shorter risers (5-5.5″ low-deck applications). 1×10 PT (9.25″) for over-tall risers (rare — only if you're hiding the gap behind a thicker face). Composite risers in matching sizes (Trex, TimberTech, Fiberon all sell 1×8 fascia/riser stock).

How wide should stair risers be?

Match the stair width — typically 36-48″. IRC R311.7.1 requires stairs over flights to be ≥ 36″ clear width. For 3 ft stair: 36″ riser board (cut from 8ft stock with waste). For 4 ft: 48″ piece (cut from 5ft or 10ft stock). Always one continuous board per riser — no butt joints in the middle.

Do I need risers if I have stringers?

Yes for closed-riser stairs (most builds). The riser board fits BETWEEN the stringer's cut faces, finished face-out. It also provides crucial vertical support to the tread above (prevents tread sag). Skipping risers = visually unfinished + tread support compromised. The only legit no-riser design is open-riser (which has its own IRC restrictions).

Should risers match the deck boards?

Aesthetic choice. Most decks: composite risers in matching color = polished look ($4.10/LF). Budget builds: PT pine risers painted to match composite ($1.95/LF + paint). Premium builds: PVC risers ($5.20/LF) for moisture resistance + matching aesthetic. Don't mix PT raw + composite — looks unfinished.

How tall can my stair risers be?

IRC R311.7.5.1: max 7.75″ — strictly enforced by inspectors. Steps over this are dangerous (CPSC injury data shows 80% of stair falls correlate with steeper-than-spec stairs). Most comfortable: 7″. Steep-but-legal: 7.5″. Code maximum: 7.75″. Above 7.75″ = automatic inspector callback regardless of design intent.

How do I install closed risers?

Cut each riser to stair-width length. Pre-finish (paint or stain) all 6 sides before install — once mounted, the bottom edge is hard to coat. Slide into the cut notch in each stringer pair (the rise cut between two run cuts). Face-screw from outside the stringer at top + bottom (4 screws per riser). The tread above sits ON TOP of the riser board, hiding the top fastener.

Stair · riser count + IRC compliance

Stair Riser Calculator

Riser board count + linear ft + material cost for any stair style. Closed (standard, 1 board per step), open (no boards — modern aesthetic, IRC-restrictive), skirt-only (side panels). Auto-validates IRC R311.7.5.1: max riser 7.75″ + open-riser openings ≤ 4″ sphere. 4 materials (PT/cedar/composite/PVC).

IRC R311.7.5.13 styles4 materials

3·Riser styles

7.75″·IRC max

4″·Sphere test

Auto·Compliance flag

Inputs

Step countrisers count

Stair widthft

Riser heightIRC max 7.75″

Style

Material

Risers · closed

515 lf · $29

Risers

closed

Linear ft

3ft × 5

Material cost

pt pine

IRC R311.7.5.1 compliance

5 closed risers @ 7.25″

IRC R311.7.5.1

Standard closed-riser stair. 5 riser boards × 3 ft = 15 LF. Material: pt pine @ $1.95/LF.

Risers cut from 1×8 PT pine (7.25″ actual covers up to 7.25″ riser). Open-riser openings must be smaller than a 4″ sphere — usually NOT compliant for residential at typical riser heights.

How to use

How to use the deck calculator in 3 steps.

Enter step count + stair width

Step count from Number of Steps Calculator. Stair width 3 ft typical (36″), 4 ft for wider, 5 ft for grand entry.

Enter riser height per step

From Number of Steps Calculator. Typically 6.5-7.5″. The riser height drives both lumber selection and open-riser compliance.

Pick style

Closed (most common — solid riser between treads). Open (no riser board — modern look, IRC-restrictive). Skirt-only (riser side-panel covers stringer end but no individual risers — non-standard).

Pick material

PT pine 1×8 ($1.95/LF — standard). Cedar ($3.20). Composite ($4.10 — matches deck). PVC ($5.20 — premium).

How we calculate

How DeckMath calculates the result — IRC 2021 sources.

The Stair Riser Calculator counts riser boards + linear feet + material cost for any stair style (closed, open, skirt-only). Auto-validates IRC R311.7.5.1: max riser 7.75″ + open-riser openings ≤ 4″ sphere. Closed risers use 1×8 PT typically (covers 7.25″ riser). Open risers expose the under-stair void (modern look) but require the opening to be small enough that a 4″ sphere can't pass — limits riser height to ~5″ for compliance, which means most open-riser stairs aren't IRC-compliant for residential.

IRC references

IRC R311.7.5.1 — Riser max 7.75″ + uniformity ±3/8″
IRC R311.7.5.1 — Open riser openings ≤ 4″ sphere passage

IRC 2021 R311.7.5.1 riser + sphere passage tests. Lumber pricing 2026-Q1.

Riser count

count = step_count (for closed); 0 (for open or skirt-only)

Closed-riser stairs have one riser board per step. Open-riser stairs have NO riser boards (the void IS the design). Skirt-only puts the riser material as side-panels only.

Riser linear feet

lf = riser_count × stair_width

5 closed risers × 3 ft = 15 lf. Each piece 1×8 (or matching size for non-7.25″ risers).

Open-riser compliance

opening = riser_height - tread_thickness; must be ≤ 4″ per IRC R311.7.5.1

Open-riser opening = riser height minus the tread thickness (~1″). For 7″ riser: 7 - 1 = 6″ opening → FAILS IRC 4″ sphere test. Only sub-5″ risers (very low decks) make open-riser stairs IRC-compliant for residential.

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Deck calculator questions, answered.

Number of Steps Calculator

IRC-compliant step count from total rise + ideal step height. Auto-enforces IRC R311.7.5.1 max riser 7.75″ + uniformity ±3/8″. Pair with Stringer Length + Rise & Run calcs.

Stair Tread Calculator

Tread board count, total LF + waste, riser boards, fasteners — across 6 materials (PT, composite, Ipe, Cumaru, cedar). IRC R311.7.5 cross-validated.

Deck Stair Calculator

Risers, treads, stringer hypotenuse, and BoM for any deck height — IRC 2021 R311.7 compliant with auto handrail + landing-pad sizing.