Shav's Carpentry Calculator

Floor Framing

Bearer & joist layout for a rectangular floor. Bearers run the long way and carry the joists; joists run across on top, spaced closely.

Plan view — bearers (thick, along length) under joists (thin, across width)

Floor length (bearer direction)

Floor width (joist span)

Bearer spacing (across width)

Joist spacing (along length)

Overhang past bearer/wall

Add 2 end trimmer joists (perimeter)

How this is calculated

Wall Framing

Stud count, plates, noggings and opening trims for one wall. Add up to two openings (door/window).

Elevation — studs, plates, noggings & openings

Wall length

Stud height (frame, plate to plate)

Stud spacing

Plate thickness (each)

Top plates (1 or 2)

Opening A

Include

Width

Type

Opening B

Include

Width

Type

Lintel bearing, each end

How this is calculated

Ceiling Framing

Ceiling joists across the room, with an optional hanging beam + struts where the span is too long for one joist.

Plan view — ceiling joists, hanging beam & struts

Room length (joists run along, spacing direction)

Room width (joist span)

Joist spacing

Span needs a hanging beam

Max strut spacing under beam

How this is calculated

Roof Pitch & Rafters

Rise, rafter length and cut angles from span and pitch. Drag the slider or pick a preset — the pitch here also drives the birdsmouth & roof covering cards below.

Section — rise / run / rafter length, drawn true to the pitch angle

Roof pitch22.5°

–rise : 12

–mm per m

–grade %

–pitch factor

Roof type

Overall span (wall to wall)

Eave overhang

Ridge board thickness

Building length (for ridge / hips)

Rafter spacing (cut roof only, not trusses)

How this is calculated

Bird’s Mouth (Birdsmouth) Cut

Seat cut & heel cut dimensions where the rafter notches over the top plate — checked against the AS 1684 one-third depth rule. Uses the pitch set above.

Rafter tail, zoomed — seat cut, heel cut & the 1/3-depth limit line

Rafter (timber) depth

Top plate width

Seat cut length

How this is calculated

Roof Covering & Battens

Batten rows and roofing-sheet count for the roof above. Uses the pitch, span, overhang and building length from the rafter card.

One roof slope, seen face-on — batten rows & sheet cover widths

Batten spacing (along slope)

Sheet cover width

Gable overhang each end

How this is calculated

Roof Trusses (Fink layout)

Truss count along the building and chord/web lengths for a standard Fink (W) truss.

Single Fink truss, drawn to the current span & pitch

Span

Pitch preset

Truss spacing (centres)

Building length

Overhang

How this is calculated

Stairs

Riser/going split from floor-to-floor height, checked against NCC comfort & safety limits.

Section — risers, goings & stringer

Total rise (floor to floor)

Target riser height

Going (tread run, used as entered)

Stair width (clear)

How this is calculated

Decking

Board count, lineal metres, joists and fixings for a rectangular deck. Boards run across the joists.

Plan view — boards (with gaps) over joists

Deck length (board direction)

Deck width (across boards)

Board width

Gap between boards

Joist spacing

Bearer spacing (across width)

Post spacing (along bearers)

Waste allowance%

How this is calculated

Set-out & Squaring

Check a rectangular set-out is square using the diagonal, and get 3-4-5 triangle multiples for pegging out on site.

Plan — both diagonals equal means the set-out is square

Set-out length

Set-out width

Measured diagonal (optional — to check yours)

How this is calculated

Sheet Materials

Sheets needed to cover an area — flooring, plasterboard, cladding or bracing ply. Pick a preset sheet size or enter your own.

Area to cover, tiled with the chosen sheet size

Area length

Area width

Sheet length

Sheet width

Waste / cutting allowance%

How this is calculated

Concrete — Slab & Post Holes

Volume and premix-bag count for a slab pour or a run of post holes (stumps, fence posts, deck footings).

A10

Slab section or post-hole section, to the current dimensions

Pour type

Length

Width (trench width for strip)

Thickness / depth

Waste allowance%

Bag size

Bags per m³ (20 kg basis — edit to your brand)#

How this is calculated

Timber Take-off

Turn a total linear length into stock lengths to order, with waste allowance and a rough cost.

A11

Stock lengths cut, with offcut/waste shown

Total length required

Waste allowance%

Stock length

Price per lineal metre (AUD, optional)$

How this is calculated

Rates & Assumptions

Nothing here is pre-filled with a market price — rates vary by supplier, region and date, so you enter your own from a current quote. Everything below multiplies live quantities pulled from sheets A1–A11.

A12

Tip: fill this in once from your supplier quote, then export it (below) so it carries over next time you open this file.

Framing timber (framing/trusses)$/m

Decking timber$/m

Sheet material (A9)$/ea

Roofing sheet pricing method

Roofing sheet (per sheet)$/ea

Roofing sheet (per lineal m)$/m

Roof battens$/m

Deck posts (incl. footing prep)$/ea

Concrete pricing method

Concrete ready-mix$/m³

Concrete premix bag$/bag

Roof structure priced from

Pick one — a job is framed with trusses or cut rafters, never both, so only the selected sheet's timber is costed.

Hardware, fixings & consumables%

Contingency%

Margin / overhead%

Add GST

GST rate%

Total floor area (for $/m²)m²

How this is calculated

Rate persistence: if this file is open inside Claude's own artifact viewer, rates save automatically in the background. Opened as a plain downloaded file in a normal browser tab, that background storage isn't available — use Export to save a small .json of your rates, and Import to load it back in next time. Either way, nothing is sent anywhere; it all stays on your device.

Materials — Pulled Live From Your Sheets

Read-only: change a dimension on any sheet (A1–A11) and these update automatically. Edit the source sheet, not this table, to change a quantity.

A12

Category	Quantity	Rate	Cost

Preliminaries, Labour, Plant & Extras

Everything a quantity sheet can't see — site costs, labour hours, hire, anything custom. Starter rows are provided; edit, remove or add as many as you need.

A12

Labour by hours: the quickest honest labour estimate is hours × charge-out rate. Fill these two and the line is added below automatically — or leave them at 0 and type a fixed labour $ in the row list instead. Use one method, not both, or labour double-counts.

Estimated labour hourshrs

Labour charge-out rate$/hr

Grand total, by share of cost

Grand total (incl. GST) $0

How this is calculated

Pitch Converter

Enter any one format and get all the others. Unlike the roof-tab slider, this works in reverse — type a rise:12 ratio and read the degrees back.

A13

Degrees°

Rise : 12 (imperial ratio):12

Rise per metre (mm/m)mm/m

Slope grade%

Pitch factor (rafter multiplier)×

How this is calculated

All five formats are different ways to express the same angle. The tangent of the pitch converts between them.

tan(θ) = rise ÷ run Rise:12 = tan(θ) × 12 mm per m = tan(θ) × 1000 Grade % = tan(θ) × 100 Pitch factor = 1 ÷ cos(θ) (rafter length per unit of run)

Entering any one solves back through the tangent (or arccosine for the pitch factor) to get the angle, then forward to all the other formats.

Mitre Angle

Saw setting for joining two pieces at a corner. For a standard 90° corner the mitre is 45° — this handles non-square corners (bay windows, splayed walls).

A13

Plan view — corner angle and the mitre cut

Corner angle (between walls)°

How this is calculated

Compound Mitre

When a piece is both sloped (raked) and turning a corner — like a handrail at a landing, or crown moulding at a non-level ceiling — you need two saw settings at once: a blade tilt and a mitre angle. Enter the slope and the plan corner and this gives you both numbers for the saw.

A13

3D corner — slope + plan angle → blade tilt + mitre

Slope angle (rake)°

Corner angle in plan°

How this is calculated

Pythagoras Solver

Enter any two sides of a right triangle — the third is calculated. Faster than the set-out sheet when you just need a quick hypotenuse or a missing leg.

A13

Right triangle — a, b and hypotenuse c

Side a

Side b

Hypotenuse c

How this is calculated

Circle, Arc & Chord

For arched openings, curved decks, bullnose verandahs — enter a radius and an arc angle (or a chord and sagitta) and get all the dimensions.

A13

Arc, chord & sagitta from a radius and angle

Radius

Arc angle (central angle)°

How this is calculated

Fraction ↔ Decimal

Convert between fractions and decimals for reading imperial tape measures. Enter either side and the other updates.

A13

Whole number

Numerator (top)

Denominator (bottom)

Decimal equivalent

Metric equivalent

How this is calculated

A fraction is just the numerator divided by the denominator, added to the whole number. The metric equivalent multiplies the decimal inches by 25.4 mm/inch.

Decimal = whole + (numerator ÷ denominator) Metric = decimal inches × 25.4 mm

Timber Volume & m³ Pricing

Convert lineal metres of a timber section into cubic metres — hardwood and some suppliers price by the m³, not the lineal metre.

A13

Total lineal length

Section width

Section depth

Price per m³ (AUD, optional)$

How this is calculated

Standards Quick Reference

What each calculation above is actually checked against. Typical figures only — always confirm against the current published standard for your wind classification, species and grade.

A14

AS 1684 (Parts 1–4)

Residential timber-framed construction. Covers stud/joist/rafter spacing, tie-down, bracing and general framing practice used across every sheet in this tool.

AS 1684 Supplement 1

The actual span tables (Tables T21–T27 and similar) that turn a span + load width + wind classification into a real timber size and grade. This tool does not replace those tables.

AS 4440

Installation of nail-plated timber roof trusses. Real trusses are engineered products from a truss manufacturer — the truss sheet here is for geometry/estimating, not final design.

AS 1720.1

Timber structures — design capacities for structural timber members.

NCC Volume Two, Part 3.4 / 3.9.1

Framing provisions (3.4) and stair construction requirements (3.9.1) for Class 1 & 10 buildings — riser/going limits used on the Stairs sheet.

AS 2870 / AS 3600

Residential slabs & footings, and concrete structures — relevant to the Concrete sheet. Bag counts there are estimating figures; structural slabs need engineered mix specs (strength grade, slump, cover).

AS 1170 / deck loads

Decks over 1 m need balustrades and attract specific imposed loads — joist/bearer sizes for the Deck sheet come from span tables, not this tool.

WHS Act 2011 (WA) & Regs

Work at height over 2 m is high-risk construction work and needs a SWMS — applies to most roof, truss and covering work here.

Typical spacing used as defaults (confirm against span tables)

Element	Typical spacing	Notes
Floor joists	450 mm (600 mm also common)	Tighter spacing for sheet flooring spans further before deflection limits bite
Floor bearers	1200–1800 mm	Depends on joist size/species and load width
Wall studs	450 mm or 600 mm	450 mm common under heavier claddings/tiles
Wall noggings	≤1350 mm vertical rows	Rows of horizontal blocking between studs
Ceiling joists	450 mm or 600 mm	As per ceiling lining and span
Roof trusses	600 mm (some 900–1200 mm)	Set by truss design, sheeting/batten spans
Common rafters	450–600 mm	Cut roofs only (not truss roofs)
Roof battens (sheet roof)	~900 mm	Tile battens much closer (tile-specific, ~330 mm)
Deck joists	450 mm	Closer for thin or diagonal-laid boards
Stair riser	115–190 mm	NCC Housing Provisions min–max
Stair going	240–355 mm	NCC Housing Provisions min–max
Stair 2R + G	550–700 mm	Slope relationship (comfort) range

Formula Reference

Every formula this calculator uses, in one place — for study, checking hand calcs, or working on paper when the phone's flat. θ = pitch angle. All lengths in consistent units.

A15

A1Floor Framing

Gaps = ceil(Width ÷ max bearer spacing) → bearers = gaps + 1 Gaps = ceil(Length ÷ max joist spacing) → joists = gaps + 1 [+2 trimmers] Actual spacing = span ÷ gaps (never exceeds the nominated max) Bearer length = Length + 2 × overhang Joist length = Width + 2 × overhang

Nominated spacing is a maximum (that's how AS 1684 span tables define it), so gaps round up and members close up slightly — the actual achieved spacing is what you mark out.

A2Wall Framing

Common studs = ceil((Length − opening widths) ÷ max spacing) + 1 Actual stud spacing = net length ÷ gaps Jack + king studs = openings × 4 Nogging rows = ceil(Stud height ÷ 1350) − 1 Noggings per row = common studs − 1 Lintel length = opening width + 2 × bearing Frame height = stud height + plate thickness × (1 + top plates)

A3Ceiling Framing

Ceiling joists = ceil(Length ÷ max spacing) + 1 (actual = L ÷ gaps) Struts under beam = ceil(Width ÷ strut spacing) − 1

A4Roof — Rafters

Run = Span ÷ 2 (skillion: Run = full Span) Rise = Run × tan(θ) Rafter = (Run − ridge ÷ 2) ÷ cos(θ) + overhang ÷ cos(θ) Plumb cut = θ Seat cut = 90° − θ Hip rafter (equal-pitch) = √(2 × Run² + Rise²) Ridge (gable) = building length + 2 × gable overhang Ridge (hip) = building length − span Rafter positions (cut roof) = ceil(building length ÷ max rafter spacing) + 1 Total common rafter timber = positions × sides × rafter length + ridge Hip rafters = 4 × hip rafter length (one per corner)

The hip formulas assume an equal-pitch hip — the hip runs at 45° in plan at any roof pitch. Unequal or Dutch hips need different geometry. Rafter count only applies to a cut roof — use the Trusses sheet instead for a truss-framed roof, and don't cost both.

A4Bird's Mouth

Heel (plumb) cut height = seat cut × tan(θ) ← for marking out Notch depth into rafter = seat cut × sin(θ) ← for the depth rule Maximum notch = rafter depth ÷ 3 (AS 1684 practice) Bearing guide: seat cut ≥ ⅔ plate width, ≤ full plate width

Two different numbers from the same cut — heel height is vertical, notch depth is perpendicular to the rafter. The one-third rule checks the notch depth, not the heel.

A4Roof Covering & Battens

Slope length = (Run − ridge ÷ 2) ÷ cos(θ) + overhang ÷ cos(θ) Batten rows per slope = ceil(slope ÷ max spacing) + 1 Batten lineal = rows × (building length + 2 × gable OH) × slopes Sheets per slope = ceil(run length ÷ sheet COVER width) Roof surface area = slopes × run length × slope length Fascia: gable/skillion = 2 × run length Fascia: hip = 2×(L + 2×OH) + 2×(span + 2×OH)

Use the profile's cover width (762 mm corrugated/Trimdek, 700 mm Klip-Lok), not the raw sheet width — side laps eat the difference.

A5Trusses (Fink)

Trusses = ceil(building length ÷ max centres) + 1 (actual = L ÷ gaps) Top chord = Run ÷ cos(θ) + overhang ÷ cos(θ) Bottom chord = span Main web ≈ √((span ÷ 4)² + (rise ÷ 2)²)

Web length is an estimating approximation — exact webs, angles and plates come from the truss manufacturer's design.

A6Stairs

Risers = round(total rise ÷ target riser) Actual riser R = total rise ÷ risers Goings = risers − 1 Total going = goings × G (G entered directly) Stringer = √(total rise² + total going²) Stair pitch = arctan(R ÷ G) NCC checks: R 115–190 · G 240–355 · 2R + G 550–700 · ≤ 18 risers/flight

A7Decking

Board rows = ceil((Width + gap) ÷ (board width + gap)) Board lineal = rows × Length × (1 + waste%) Joists = ceil(Length ÷ max spacing) + 1 Bearers = ceil(Width ÷ max bearer spacing) + 1 Posts = bearers × (ceil(Length ÷ max post spacing) + 1) Footings = posts (volume → Concrete sheet, post holes) Screws = rows × joists × 2

A8Set-out & Squaring

Diagonal = √(Length² + Width²) 3-4-5: sides 3u and 4u → diagonal exactly 5u (3² + 4² = 5²)

Check side lengths first, then both diagonals — equal diagonals prove square only when opposite sides already match.

A9Sheet Materials

By area = ceil(Area × (1 + waste%) ÷ sheet area) By grid = ceil(L ÷ sheet L) × ceil(W ÷ sheet W), best of both orientations Order between the two — closer to grid when joints must land on framing

A10Concrete

Slab / strip footing volume = L × W × thickness (depth) Post hole = π × (d ÷ 2)² × depth − post² × depth Bags = ceil(volume incl. waste × bags per m³) Bags per m³ (20 kg): Boral 108 · Bastion/Aust. Builders 100 · Dingo 110 Other bag sizes scale on mass: bags/m³ × (20 ÷ bag kg) Wet weight ≈ volume × 2.4 t/m³

A11Timber Take-off

Length incl. waste = required × (1 + waste%) Stock lengths = ceil(length incl. waste ÷ stock length) Offcut = purchased − required Cost = (purchased ÷ 1000) × price per lineal metre

A12Cost Estimate

Category cost = quantity (from source sheet) × your rate Materials subtotal = Σ every category Fixings base = Materials subtotal − concrete − A11 pass-through Total materials = Materials subtotal + Fixings base × fixings % Labour = hours × charge-out rate (or fixed $ rows) Cost subtotal = Total materials + Additional items (preliminaries/labour/plant/other) Contingency $ = Cost subtotal × contingency % Margin $ = (Cost subtotal + Contingency $) × margin % GST $ = (Cost subtotal + Contingency $ + Margin $) × GST % GRAND TOTAL = Cost subtotal + Contingency $ + Margin $ + GST $ $/m² = Grand total ÷ floor area

Roof structure timber is pulled from either Trusses (A5) or cut rafters (A4) — never both. Every $ rate is user-entered; nothing is a built-in market price.

A13Toolbox — Pitch & Angles

tan(θ) = rise ÷ run Rise:12 = tan(θ) × 12 mm per m = tan(θ) × 1000 Grade % = tan(θ) × 100 Pitch factor = 1 ÷ cos(θ) Mitre = corner angle ÷ 2 Compound mitre: Blade tilt = arctan(sin(corner ÷ 2) × tan(slope)) Mitre angle = arctan(cos(slope) × tan(corner ÷ 2))

A13Toolbox — Geometry

Pythagoras: c = √(a² + b²) · a = √(c² − b²) · b = √(c² − a²) Arc length = radius × angle (radians) Chord = 2 × radius × sin(angle ÷ 2) Sagitta = radius × (1 − cos(angle ÷ 2)) Radius from chord + sagitta: r = chord² ÷ (8 × sagitta) + sagitta ÷ 2 Circumference = 2πr · Circle area = πr² Fractions: decimal = whole + num ÷ den · mm = inches × 25.4 Timber volume = length × width × depth (m) → m³ Lineal m per m³ = 1 ÷ (width × depth in m)