Garden room calculator

Size your room, see the shell in 3D and preview its material quantities. Free, no sign-up; full documents in the paid pack.

Real stock lengths
Your country's building practice
No invented prices

Popular in United Kingdom

Custom design

47 × 100 mm studs · 2400 × 1200 mm OSB3 sheets

View options

Loading the 3D view…

Wall layers and foundation guide

What's inside the wall

Outside → inside. Tap a layer.

Breather membrane

Stops rain that gets past the cladding but lets damp vapour out.

Every layer ticked here is counted in your material list.

Which base suits your garden

Tap one to use it.

Ground: Most soils, slopes. Not solid rock.
Digging: None
Concrete: None
Waiting: Build the same day
Floor: Raised on bearers, air under the floor

This base is counted in your material list. Ground conditions vary, so check yours before you dig.

Width

4 m↑↓ 50 mm · shift ×10

Depth

3 m↑↓ 50 mm · shift ×10

Wall height

2.3 m↑↓ 50 mm · shift ×10

Roof

Base

Door width

1.8 m↑↓ 50 mm · shift ×10

Doors

Door wall

Position on that wall

Storage bay

Covered porch

Frames and glass

Roof covering

Insulated and linedYear-round room rather than a summer shell

Windows

Window wall

More windows on

Cheapest boarded finish. Fixed board over board on battens. · 15–20 years · Treat every 2–3 years

What you buy

Treated feather edge, 47 × 100 mm studs at 16 in centres, worked out to United Kingdom practice.

12.0 m²

Floor

Studs

Sheets

Size: 4 m × 3 m
Floor area: 12 m²
Wall height: 2.3 m

Height to roof: 2.52 m
Cladding: Treated feather edge
Roof: Flat, laid to a fall
Base: Ground screws and bearers
Studs: 48 × 2.36 m (47 × 100 mm studs)
Plates: 43 m total
Noggins: 32
Floor joists: 11 × 3 m
Roof joists: 11 × 3.6 m
Sheathing: 11 2400 × 1200 mm OSB3 sheets (includes 12% cutting allowance)
Floor deck: 5 sheets (includes 10% cutting allowance)
Roof deck: 6 sheets (includes 10% cutting allowance)
Internal lining: 16 sheets (includes 12% cutting allowance)
Cladding boards: 67 lengths (includes 10% cutting allowance)
Battens: 24 lengths (85 m total)
Breather membrane: 1 roll
Roof covering: 17.7 m² of epdm rubber (includes 15% cutting allowance)
Roof trim: 16 m total
Corner boards: 4 lengths, one up each outside corner
Insulation: 11 packs of 100 mm insulation
Vapour control layer: 1 roll
Ground screws: 12
Bearers: 13 m total
Door set: Sliding doors, 2 panels, 1.8 m wide, anthracite aluminium frame
Windows: 1 standard, anthracite aluminium frame
Frame fixings: 627
Cladding and roof fixings: 1008
Sheet screws: 1710

28 more lines for your exact size, plus a cut list on standard stock lengths, so you order once instead of going back for what was missed

Instant PDF + CSV · One payment · No subscription

Checked against United Kingdom practice

Height: 2.52 m to the top of the roof. Above the usual limit close to a boundary, so check before you build.

A shell take-off and a sanity check, not a structural design, an electrical design or a planning decision.

Build it right first time — $9

A missed fixing or a wrong length usually means another trip to the yard. The Full Build Pack lists every line counted from this drawing, in the stock lengths merchants sell, with a cut list and the order to build in.

Garden room build pack

Your project

Prepared with BuildPlot3D

buildplot3d.com — this band is on every free pack, above your own name.

Pay once, no account needed first. Use the email you want the job kept under; we set up your login from it after payment.

One payment
No subscription
No account needed first
PDF + CSV straight away
Delivered immediately

Preview a full sample pack (opens in a new tab)

How the cut list reads (example layout)

Each stock length the yard sells, with the pieces to cut from it and what is left over.

Yard order sheet · setting out · build order

24 order lines · 48 studs · 11 sheets

Filled in for this job with the $9 pack

What $9 adds

Full material quantities beyond the free preview
Dimensioned framing plan and the exact cut list, packed into stock lengths
CSV merchant order file, ready for a supplier or spreadsheet
Setting out: the diagonal to pull so the frame is square before anything is fixed
Yard order sheet: only things a merchant can hand over, each line checked and in your own units, with a box to tick
Build order: each stage in sequence, with the check that goes with it
Your company name on the PDF and the shared page, with our line gone

Building it yourself? One length cut short costs more than this pack. You get the diagonal to square the frame, the counter sheet to tick off at the yard, and the order to build in.

Quoting a customer? The same job goes out under your own name, with our line gone. Per job, no subscription to start.

Still free: the 3D drawing, the take-off on screen, a summary PDF and your own prices.

Type in what your supplier charges and the room gets costed. Leave it empty and you keep the quantities only.

Garden room calculator: what goes into the shell

A garden office, summerhouse or workshop starts with a footprint. This calculator turns your room dimensions and material choices into a shell material take-off, with a 3D model of the same design.

Dimensions, roof and openings: Set width, depth and wall height. Choose a flat, mono-pitch, apex or parapet roof, then the cladding, roof covering, doors, windows and insulation. Base choices are ground screws, concrete pads, a concrete slab or existing paving.
Material quantities, not just floor area: The take-off covers studs, plates, floor joists, roof framing, sheets, cladding, battens, membranes, roof covering, insulation, base materials and fixings as applicable to your design. Door and window openings feed the same calculation.
UK, Ireland, US and Canada: Country changes the regional framing practice, stock sheet sizes and available material choices. Metres and feet are display options; switching units is not the same as changing the country.
Costs use your supplier's rates: No average building costs or invented material prices are supplied. Leave rates empty for quantities only. Enter your own rates for a cost estimate; unpriced items are left out and listed as missing, so a partial estimate is not a full project budget or a supplier quote.
Free preview and paid documents: The 3D model, checks, first take-off lines and summary export are free without sign-up. The remaining quantities and build documents belong to the paid Full Build Pack, including dimensioned plans, cut lists and merchant order sheets. The pack price is separate from your material costs.
A shell take-off, not an approval: This is not structural engineering, electrical design or a planning decision. It does not specify a complete fitted-out room. Confirm ground conditions, loads, foundations, opening specifications and local requirements with the relevant supplier or qualified professional before ordering or building. Regional starting styles and checks do not certify a design.

4 m × 3 m garden room

Treated feather edge · 2.3 m walls