DeckMath
railing · guardrail · stair handrail · IRC R312

Railing Linear Feet Calculator

How much railing do you actually need? DeckMath sums perimeter minus house-attached sides minus gates, plus angled stair handrail (hypotenuse), with material-specific post spacing (4-6′ o.c.). 5 tiers from PT cap ($24/lf · DIY) to tempered glass ($105/lf · luxury). Auto IRC R312 guard-height flag + R311.7.8 stair-handrail check.

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Get 2–3 free quotes
4 shapes · rect / L / U / custom5 materialsIRC R312 + R311Auto post countBoM + share + PDF
5·Material tiers
4-6′·Post spacing o.c.
36/42″·Guard height
R312·IRC code

Inputs

Deck shape

Main rectangle

ft

ft

Full perimeter56′
Open (after attached)40′
Guard LF (after gates)40′
in

⚠ IRC R312 — 36″ guardrail required.

Stairs

in

in

Hypotenuse / stringer5.48′
Handrail LF (all stairs)5.48′

Results

IRC R312 guardrail required (36″) · IRC R311 stair handrail required · DIY tier 1

Total railing
order 48.66′ (7% waste)
Posts
6′ max o.c.
Project total
Low $4,056 · Northeast
$/lf installed
Low $89

Perimeter diagram

16′12′house1 stair
Railing required (40′) House-attached (no rail) Stair (5.48′ handrail)

Guardrail required — 36″ off grade ≥ 30″

IRC R312.1.1 + R312.1.2

IRC R312.1.2 mandates a 36″ minimum guardrail on the open sides of decks more than 30″ above grade. 40 LF of guardrail in the BoM.

Stair handrail required — 5 risers ≥ 4

IRC R311.7.8.1 + R311.7.8.4

IRC R311.7.8.1 requires a handrail on at least one side of stairs with 4+ risers. 5.48′ hypotenuse per side · one side × 1 stair = 5.48 LF of angled handrail. Returns at top + bottom (R311.7.8.4) included as bracket-kit line item.

Post spacing — max 6′ o.c. (12 posts total)

IRC R312.1.4 + manufacturer spec

6′ max post spacing meets IRC R312.1.4 + manufacturer spec. Composite sleeves slip over a 4×4 PT structural post.

4″ sphere rule — opening limit verified

IRC R312.1.3.1 + R312.1.3.3

IRC R312.1.3.1 requires that a 4″ sphere cannot pass through any guardrail opening. Baluster centers at ≤4″ (use the Baluster Spacing Calculator to size individual baluster placement once total LF is set). Stair triangle (R312.1.3.3) limited to 4-3/8″ — handrail brackets account for this.

Material tier 1 — DIY-friendly

Manufacturer install spec

Best value mid-market. Color-matched cap, 25-yr warranty, no repaint. DIY-friendly w/ pre-cut kits.

Composite cap rail w/ aluminum balusters (Trex Signature / TT Classic)
49 lf ordered · 45 lf actual · 7% waste · $42/lf installed-equiv
49 lf
$2,044
Composite-sleeve 4×4 posts (matching cap)
12 posts · 10 guard + 2 stair posts · max 6′ o.c.
12 post
$1,020
Surface-mount post bases (Simpson APB / DTT2Z)
12 post bases bolted through decking into framing
12 ea
$312
Stair handrail brackets + returns (IRC R311.7.8.5)
4 brackets · code-compliant 1.5″ wall clearance · returns at top/bottom
4.0 ea
$56
Materials subtotal
$3,432

Cost breakdown

Materials
$3,157 – $3,432
Labor
$899 – $1,099
Soft costs
$0 – $0
Subtotal
$4,056 – $4,530
Contingency (8%)
$362
Project total
$4,056 – $4,893
Cost per linear foot (45.48 lf)
$89 – $108

2026-Q1 pricing. Ranges reflect contractor vs DIY purchase, regional supplier variance, and the 7% material waste typical of composite cap rail w/ aluminum balusters (trex signature / tt classic). Permit fees are average residential — your local AHJ may charge more. Always verify code with your local inspector before ordering.

How to use

How to use the railing linear-feet calculator in 5 steps.

  1. 1

    Pick the deck shape

    Rectangle (most common — 2L+2W perimeter), L-shape (main rect + leg, minus shared edge), U-shape (main rect + two legs), or Custom LF for unusual layouts. For Custom, enter the total OPEN perimeter directly (already net of attached sides). L and U-shape inputs accept the secondary leg's length × width independently.

  2. 2

    Set deck dimensions + attached sides

    Length × width in feet. Attached-sides count: 0 = freestanding (full perimeter needs rail), 1 = one side against house (subtract length), 2 = corner-nested (subtract length + width). House-attached sides don't need guardrail per IRC — only the open sides do.

  3. 3

    Enter stair geometry

    Stair count (0-3 landings), total rise (deck height to grade in inches), and total run (stringer horizontal in inches). DeckMath computes the stringer hypotenuse via √(rise² + run²) and adds that length per stair side. Toggle 'handrail both sides' for wider stairs (>44″) per IRC R311.7.8.

  4. 4

    Add gates if any

    Each gate subtracts 3 feet from the guardrail LF (standard residential gate width). Gates are separately costed line items with self-closing + child-safe latch hardware (pool-code compliant). 0-4 gates supported.

  5. 5

    Pick material tier + state

    PT cap ($24/lf, DIY tier 1), composite cap ($42/lf, DIY tier 1 — best value), cable ($58/lf, DIY tier 2 — premium open view), glass ($105/lf, pro-only tier 3 — luxury), aluminum ($48/lf, DIY tier 1 — fastest install). State selection adjusts labor cost via regional multipliers (12 US regions).

How we calculate

How DeckMath calculates this — IRC 2021 sources.

The Railing Linear Feet Calculator sizes the total guardrail + handrail you need for a deck — perimeter minus house-attached sides minus gates, plus the angled stair handrail run, with code-compliant post layout. Pick deck shape (rectangle, L-shape, U-shape, or custom LF), attached-side count, stair geometry, and one of five material tiers: pressure-treated cap rail ($24/lf · DIY), composite cap ($42/lf · best value), cable ($58/lf · open view), glass ($105/lf · luxury), or aluminum picket ($48/lf · low maintenance). DeckMath returns ordering LF including waste, post count at material-specific max spacing (4-6′ o.c. per IRC R312 + manufacturer instructions), the IRC-required guard height (36″ or 42″), and a BoM with installed-cost ranges accounting for regional labor (12 US regions) and permit fees. Distinct from the Baluster Spacing Calculator (D.1, MVP) which fills a known railing length with code-compliant balusters — this calc tells you HOW MUCH RAIL you need before you start measuring balusters.

IRC references

  • IRC 2021 R312.1.1 — Guards required on open sides of decks > 30″ above grade
  • IRC 2021 R312.1.2 — Guard height 36″ minimum (residential); 42″ above 6′ in some jurisdictions
  • IRC 2021 R312.1.3.1 — 4″ sphere rule (no opening allows passage of 4″ sphere through guardrail)
  • IRC 2021 R312.1.3.3 — Stair triangle 4-3/8″ opening limit
  • IRC 2021 R311.7.8.1 — Handrail required on at least one side of stairs with 4+ risers
  • IRC 2021 R311.7.8.3 — Continuous handrail along entire stair flight; returns at top/bottom
  • IRC 2021 R311.7.8.5 — Handrail clearance 1.5″ minimum from wall
  • IRC 2021 R301.5 — Guard live load 50 lb single point applied any direction

Railing pricing 2026-Q1: PT cap $24/lf, composite cap $42/lf (Trex Signature / TimberTech Classic), aluminum picket $48/lf (Westbury / Fortress), cable rail $58/lf (Feeney / Atlantis), tempered glass $105/lf (10mm panel). Labor $12-45/lf by material. Waste 4-10% by material. Post spacing per IRC R312.1.4 + manufacturer.

Rectangle perimeter
P = 2·(L + W)

Sum of all four sides. 16×12 rectangle = 56 LF perimeter. With 1 house-attached side (length = 16′), open perimeter = 40 LF.

L-shape perimeter
P = 2·(L + W) + 2·(L₂ + W₂) − 2·shared

Main rectangle plus leg rectangle, minus twice the shared edge where the leg attaches to the main. For a 16×12 main + 8×6 leg (shared edge = 6′): 56 + 28 − 12 = 72 LF.

Stair handrail hypotenuse
H = √(rise² + run²) / 12

Stringer length per stair. For a 36″ rise + 55″ run stair: √(36² + 55²) / 12 = √(1296 + 3025) / 12 = √4321 / 12 ≈ 5.48 LF per side. Two-side stairs (>44″ wide) double this.

Ordering LF (with waste)
L_order = L_total × (1 + waste%)

Waste varies by material: PT cap 10% (miter cuts + end loss), composite 7%, cable 4% (cut-to-length kits), glass 5%, aluminum 6%. For 40 LF composite cap: 40 × 1.07 = 42.8 LF ordered.

Post count
n = corners + ceil(L_guard / max_spacing) + stair_posts

Cable rail max spacing is 4′ (tension load); composite/PT/aluminum/glass all permit up to 6′. For 40 LF of cable rail in a rectangle: 4 corners + ceil(40/4) − 4 + 1 = 11 posts (guard) + 2 stair posts = 13 total.

IRC guard height
Deck > 30″ above grade → 36″ guard required (R312.1.2)

Residential decks above 30″ must have a 36″ minimum guard. Some jurisdictions require 42″ above ~72″ (commercial threshold). DeckMath flags 42″ when deck height > 72″ as a code-safety hint.

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People also ask

Railing linear-feet questions, answered.

  • Full rectangle perimeter is 2·(16+12) = 56 LF. If one side is attached to the house (most common), subtract the 16′ attached side: 40 LF of guardrail. Add ~5.5 LF per stair side for one set of stairs. So a typical 16×12 deck with one house-attached side and one stair landing needs about 46 LF of guardrail + handrail. Order 10% extra (≈51 LF) for end cuts and miter waste.

  • IRC 2021 R312.1.1 requires a 36″ guardrail on any deck surface more than 30 inches above the grade below. Stair handrail is required (R311.7.8.1) on any stair with 4 or more risers — typically when total stair rise exceeds 24 inches. DeckMath auto-flags both code triggers based on deck height and stair rise inputs. Below 30″ deck height with no stairs, railing is optional (aesthetic).

  • Installed material + labor by tier: pressure-treated cap rail $36-50/lf (DIY-friendly), composite cap $60-85/lf (best value), aluminum picket $64-90/lf (fastest install), cable rail $86-120/lf (premium open view), tempered glass panel $150-200/lf (luxury). A 40 LF guardrail in composite cap typically lands $2,400-3,400 installed. Cable adds ~40% over composite. Glass adds ~150%.

  • Material and manufacturer drive the maximum spacing. Cable rail systems limit to 4 feet on-center (cable tension creates significant horizontal load on end posts). Composite cap, PT cap, aluminum, and glass all allow up to 6 feet on-center. Corner posts always required regardless of spacing. For a 40 LF straight run with composite cap: 4 corners + ceil(40/6) − 4 + 1 = 8 posts minimum. Cable on the same run needs 11 posts.

  • IRC R311.7.8.1 requires handrail on AT LEAST ONE side of stairs with 4+ risers. Both sides are required only when the stair is wider than 44 inches per R311.7.8.2 — most residential deck stairs are 36-42″ wide, so one side is fine. Local AHJs may require both sides for stairs that serve as the only egress from a deck above 6′ — check your inspector.

  • For a 36″ rise + 55″ run stair (typical 5-riser deck stair): √(36² + 55²) ÷ 12 = 5.48 LF of angled handrail per side. Round to 6 LF for ordering. The angled handrail returns to the post at top and bottom (IRC R311.7.8.4) — DeckMath includes the bracket count + return-fittings cost in the BoM. For a 96″ deck height with two 4′ landings, total handrail run is ≈25 LF per side.

  • Material cost: PT cap rail is roughly 60% the per-LF cost of composite cap ($24 vs $42 per LF). But total installed cost narrows the gap: PT labor is similar to composite, and PT requires repainting every 2-3 years. Over a 25-year horizon, composite cap costs less than PT once you factor 8-12 repaint cycles. PT wins on year-1 cash outlay only.

  • Yes — common patterns include composite cap rail on the long open sides + cable infill on the view side (best of both worlds). DeckMath's calculator handles one material at a time, but you can run it twice (once per material zone) and sum the LF for each. Post spacing must drop to the most-restrictive zone's max (e.g., a cable section forces 4′ o.c. across that section).

  • Yes. Each gate opening (standard 36″ = 3 feet) subtracts from the guardrail LF because the gate itself replaces a section of rail. DeckMath's BoM treats gate hardware as a separate line item (~$185 per gate kit, including self-closing hinges and child-safe latch). Gates around pool decks must meet local AHJ requirements — typically self-closing + auto-latching with the latch ≥54″ from grade per ISPSC.

  • Frameless glass railing systems (Q-railing, Easy Glass) use channel mounts in the deck framing instead of vertical posts — the glass itself is the structure. They cost $180-250 per LF installed, require 12mm tempered laminated glass per IBC, and need an engineered base channel. DeckMath's 'glass' option assumes top-rail framed glass with aluminum posts; for frameless, multiply by ~1.7× and consult a glass specialist.

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