Why is a 2×4 actually 1.5″ × 3.5″?

US softwood lumber is sold by NOMINAL size — the rough-cut size before planing. After surfacing (S4S = Surfaced on 4 Sides), the lumber loses 1/2″ on each dimension for boards ≤2″ nominal thickness, and 3/4″ for thicker stock. A 2×4 starts as a rough 2×4 → planed to 1.5×3.5″ = 38×89 mm. A 6×6 post starts rough then planes to 5.5×5.5″ = 140×140 mm. Always use the ACTUAL dimensions when calculating spans, beam strength, or fitting hardware.

How many square meters is a 12×16 deck?

12 ft × 16 ft = 192 sqft = 17.84 sqm. Conversion: 1 sqft = 0.09290304 sqm exactly. Common sizes: 10×10 = 100 sqft = 9.29 sqm · 12×12 = 144 sqft = 13.38 sqm · 16×20 = 320 sqft = 29.73 sqm. The calculator gives you both directions automatically.

What's a Trex board in millimeters?

Trex 1×6 grooved boards are 0.94″ × 5.5″ × 16 ft → 23.88 × 140 mm × 4877 mm in metric. Trex 1×8 wide-board is 0.94″ × 7.25″ × 16 ft → 23.88 × 184 mm × 4877 mm. TimberTech 1×6 is slightly narrower at 5.36″ (136 mm) due to TimberTech's profile geometry. AZEK matches Trex at 5.5″. The calculator's decking mode covers all the major brands.

How do I convert square feet to board count?

Use the coverage planner mode. Enter target area (sqft or sqm), pick the board profile + length + waste %. Math: boards = ceil(area × (1 + waste) / per_board_sqft). For 240 sqft with a 5.5″ × 16 ft Trex board (= 7.33 sqft / board) + 10% waste: ceil(240 × 1.10 / 7.33) = 37 boards = 592 linear ft = 180.4 linear m.

What's the difference between US gallons and Imperial gallons?

1 US gallon = 3.785 liters. 1 Imperial (UK) gallon = 4.546 liters — about 20% larger. The calculator uses US gallons (standard in North America for concrete, paint, sealant volumes). When ordering material from UK or Australian sources, convert through liters first to avoid the gallon ambiguity. Decking sealant volumes are typically US gallons in North-American spec sheets.

How much does a 2×10 PT joist weigh?

About 3 lb per linear foot for PT southern pine (density ~30 lb/cuft, actual cross-section 1.5×9.25″ = 13.9 sqin = 0.0965 sqft). So a 16 ft 2×10 PT = ~50 lb = ~22.7 kg. A 20 ft 2×12 PT = ~80 lb = ~36 kg. For helicopter-lift or stair-up-to-elevated-deck weight checks, use the calculator's mass mode to convert.

Why does the calculator show metric mm instead of cm for lumber?

Metric lumber standards (Europe, Australia, NZ) are published in millimeters — e.g. 38×89 CLS, 45×95 SLP, 50×100 European softwood. Centimeters aren't used in the building trade. The calculator returns both mm + cm but mm is the practical unit. 38 mm = 3.8 cm = 1.5″.

Is a 'meter' deck board really 3.281 ft?

Approximately yes — 1 m = 3.2808 ft. But metric decking is typically sold in standardized lengths: 3 m (9.84 ft), 3.6 m (11.81 ft), 4.2 m (13.78 ft), 4.8 m (15.75 ft), 5.4 m (17.72 ft), 6.0 m (19.69 ft). North-American decking comes in 8/10/12/16/20 ft. When matching a metric-spec deck to North-American supply, round UP to the next 16 or 20 ft length and accept the cutoff scrap.

How many bags of concrete is 1 cubic meter?

1 m³ = 35.315 cuft. At a typical 80 lb bag yield of 0.60 cuft (Quikrete / Sakrete standard mix), 1 m³ needs ceil(35.315 / 0.60) = 59 bags before waste. With 10% waste = 65 bags. At that volume the Concrete Calculator's ready-mix breakpoint advisory triggers — delivered concrete is usually cheaper above 0.76 m³ (1 cuyd).

Can I trust these conversion factors?

Yes — all factors are NIST-published exact values (where exact) or rounded to 7+ significant digits. 1 ft = 0.3048 m (exact); 1 lb = 0.45359237 kg (exact); 1 in = 25.4 mm (exact). The calculator rounds OUTPUT to 4 decimals max for display readability — internal math is full precision. For high-precision engineering work (over 1000 m³, or > 5000 sqm), use the NIST official table directly.

7 modes · lumber nominal → mm · decking board catalog · coverage planner

Imperial / Metric Converter

Deck-focused unit conversion utility. Linear (ft / in / yd / m / cm / mm), area (sqft / sqm), volume (cuft / cuyd / cum / gallons / liters), mass (lb / kg / tons / tonnes). Lumber nominal-to-actual covering 16 sizes from 1×2 through 6×6 (with 5/4×6 standard decking). 11 decking board profiles with metric mm + per-board sqft / sqm coverage. Coverage planner: target deck area (sqft OR sqm) → board count + linear feet / meters needed.

16 lumber sizes11 decking profiles7 conversion modesNIST factorsCoverage plannerFree forever

7·Conversion modes

16·Lumber nominals

11·Decking boards

NIST·Exact factors

Inputs

Mode7 conversion modes

Valuevalue to convert

From unit

To unit (primary)

Linear conversion

16 ft4.8768 m

16 feet → meters

All conversions

From	To	Note
16 16 feet	4.8768 meters
16 16 feet	192 inches
16 16 feet	5.3333 yards
16 16 feet	487.68 centimeters
16 16 feet	4876.8 millimeters

Conversion uses NIST-published factors (2026-Q1). For lumber purchase, always round UP to next stocked length.

Need full deck materials?

The Board Foot Calculator handles lumber-volume math + species pricing. The Deck Material Calculator builds a full BoM with joists, beams, posts, footings, fasteners.

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NIST conversion factors · 2026-Q1

Linear / area / volume / mass factors per NIST Special Publication 811. Lumber nominal-to-actual per ANSI/ALSC PS 20-15 American Softwood Lumber Standard. Decking board dimensions from manufacturer spec sheets (Trex / TimberTech / AZEK / Fiberon / Deckorators, 2026-Q1).

How to use

Three steps. Permit-ready output.

Pick a mode

Linear / area / volume / mass for generic conversions. Lumber for 2×4 → 38 × 89 mm style nominal-to-actual. Decking for Trex / TimberTech / AZEK board dimensions in mm + per-board sqft. Coverage planner for board-count math from a target deck area.

Linear / area / volume / mass

Enter a value + pick the FROM unit + pick the TO unit. Calculator returns the primary conversion plus all other unit equivalents (e.g. 16 ft = 4.877 m = 487.68 cm = 4876.8 mm = 5.333 yd).

Lumber nominal-to-actual

Pick a nominal size from 1×2 through 6×6 (16 sizes including 5/4×6 standard decking). Calculator returns the actual surfaced (S4S) dimensions in inches + millimeters + centimeters. 2×4 nominal → 1.5×3.5″ actual → 38×89 mm — the actual size you'll receive after planing.

Decking board dimensions

Pick from 11 stocked decking profiles — Trex / TimberTech / AZEK / Fiberon / Deckorators 1×6 + 1×8, plus PT 5/4×6 / cedar 5/4×6 / IPE 1×6. Pick a length (12 / 16 / 20 ft). Calculator returns mm dimensions + per-board sqft / sqm coverage.

Coverage planner

Enter target deck area (in sqft OR sqm), pick the board profile + length + waste factor (default 10%). Calculator returns board count + total linear feet + total linear meters needed for purchase planning.

How we calculate

The math, fully transparent.

The Imperial / Metric Converter is a deck-focused unit conversion utility covering 7 modes — linear (ft / in / yd / m / cm / mm), area (sqft / sqm), volume (cuft / cuyd / cum / gallons / liters), mass (lb / kg / tons / tonnes), lumber nominal-to-actual (1×2 through 6×6 → actual inches and millimeters), decking-board dimensions (Trex / TimberTech / AZEK / Fiberon / Deckorators / PT / cedar / IPE → metric mm + per-board sqft / sqm coverage), and a coverage planner (target area in sqft or sqm → board count + linear feet / meters needed with waste factor). All conversions use NIST-published factors.

IRC references

ANSI/ALSC PS 20-15 — American Softwood Lumber Standard (nominal vs actual)
NIST Special Publication 811 — Guide for the Use of the International System of Units
IRC 2021 Appendix N — Imperial/SI conversion factors for residential codes

Linear / area / volume / mass factors per NIST Special Publication 811. Lumber nominal-to-actual per ANSI/ALSC PS 20-15 American Softwood Lumber Standard. Decking board dimensions from manufacturer spec sheets (Trex, TimberTech, AZEK, Fiberon, Deckorators, 2026-Q1).

Linear conversion (ft ↔ m)

1 ft = 0.3048 m (exact)

NIST 'international foot' definition. So 16 ft = 4.877 m, 20 ft = 6.096 m, 1 yard = 0.9144 m. For lumber purchase, always round UP to next stocked length — half-boards are usually non-returnable.

Area conversion (sqft ↔ sqm)

1 sqft = 0.09290304 sqm = 929.03 sqcm

Equivalently 1 sqm = 10.7639 sqft. A 240 sqft deck = 22.30 sqm. A 30 sqm deck = 322.92 sqft. Round up to nearest 5 sqft / 0.5 sqm when ordering decking.

Volume conversion (cuyd ↔ cum)

1 cuyd = 0.764555 m³ · 1 m³ = 35.315 cuft

Concrete in the US ships in cubic yards; in metric countries in cubic meters. A 3 cuyd ready-mix delivery = 2.29 m³. 1 US gallon = 3.785 liters (NOT the same as the Imperial gallon — UK Imperial gallon = 4.546 liters; this calculator uses US gallons).

Mass conversion (lb ↔ kg)

1 lb = 0.45359237 kg (exact)

Used for delivery freight planning + helicopter-lift weight checks on multi-story decks. 1 ton (US short ton) = 907.18 kg ≠ 1 metric tonne (1000 kg). A 16 ft 2×10 PT joist weighs ~50 lb / 22.7 kg.

Lumber nominal-to-actual

S4S softwood: nominal − 1/2″ for ≤2″ thickness, − 3/4″ for ≥4″

Standard US softwood is sold nominal but surfaced (S4S — Surfaced on 4 Sides) to a smaller actual dimension. 2×4 nominal → 1.5×3.5″ → 38×89 mm. 5/4×6 (standard PT decking) → 1×5.5″ → 25.4×140 mm. Always check actual dimensions when matching to a structural span chart.

Per-board sqft coverage

coverage_sqft = (width_in × length_ft × 12) / 144

A 5.5″ wide × 16 ft Trex board covers (5.5 × 192) / 144 = 7.33 sqft. For a 240 sqft deck with 10% waste, that's ceil(240 × 1.10 / 7.33) = 37 boards. Total linear feet = 37 × 16 = 592 ft = 180.4 m.

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Board Foot Calculator

Convert dimensioned lumber (thickness × width × length × quantity) to board feet across 13 species. Multi-row BoM mode, weight (lbs), regional $/bf cost range. 2026 retail.

Deck Material Calculator

Calculate exact decking boards, joists, beams, posts, footings, and fasteners for your deck — IRC 2021 compliant.

Square Footage Calculator

Deck square footage for any shape — rectangle, L, U, T, octagon, hexagon, round. Feet + inches inputs. Returns sqft, sqm, perimeter, plus quick BoM hooks to material + cost calculators.

Deck Board Calculator

Pattern-aware deck board count — straight / 45° diagonal / herringbone, with optional picture-frame border. 4 profiles × 5 materials × 5 stocked lengths. Cut-waste optimizer + hidden-clip count.

Imperial / Metric Converter

Inputs

All conversions

Need full deck materials?

Three steps. Permit-ready output.

Pick a mode

Linear / area / volume / mass

Lumber nominal-to-actual

Decking board dimensions

Coverage planner

The math, fully transparent.

IRC references

Don’t lose this estimate.

Questions, answered.

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Board Foot Calculator

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