Garden Room Size Calculator

It depends on the use. As a rule of thumb: a one-person garden office works from about 50 sq ft of internal zone space (a 3.0 x 2.4 m / 77.5 sq ft footprint); a two-person office needs around 100-130 sq ft (3.0 x 3.0 m to 4.0 x 3.0 m); a lounge with a 3-seat sofa needs about 113 sq ft (3.6 x 3.0 m); and a guest room with a queen bed and ensuite needs about 150 sq ft (4.0 x 4.0 m). Use the calculators above for your exact furniture.

Allow 50 sq ft per person for desk, chair and circulation, so 100 sq ft for two — plus extras. Two people with large desks and a storage cabinet need 128 sq ft (11.89 sq m), which fits a standard 4.0 x 3.0 m garden room. Add 45 sq ft if you also want a small meeting table.

Under permitted development (GPDO 2015 Class E, England), any garden building within 2 metres of a boundary must be no more than 2.5 metres high overall, and eaves must never exceed 2.5 metres. Further than 2 m from the boundary, the limit is 4 m for a dual-pitched roof or 3 m otherwise.

Usually not, if it qualifies as permitted development: it must be single storey, not forward of the principal elevation, cover no more than 50% of the garden (excluding the house footprint), respect the height limits (2.5 m within 2 m of a boundary), and not sit in a listed-building curtilage. The Planning Check mode above tests each rule. Scotland, Wales and Northern Ireland have different rules — always confirm with your local planning authority.

Often not for small structures. The base International Residential Code (R105.2) exempts one-storey detached accessory structures of 120 sq ft or less from a building permit — but many cities and counties amend that threshold to 200 sq ft, or set their own. Electrical and plumbing work needs permits regardless of size, and zoning setbacks apply separately.

Around 100 sq ft (9.3 sq m) is the practical minimum most ready-made suppliers build to — a 3.0 x 3.0 m room. Smaller pods exist (some as compact as 2.1 x 2.1 m internal, about 47.5 sq ft), but below 100 sq ft your choice of suppliers narrows sharply, so confirm minimum sizes before ordering.

This calculator uses a 50 sq ft planning allowance per person: a 60 x 30 in desk (12.5 sq ft), 36 in of chair pull-out space behind it (15 sq ft), plus a share of circulation (22.5 sq ft). Add 8 sq ft per person for a large or L-shaped desk.

Physically yes, legally it depends. In the UK, permitted development only covers buildings 'incidental to the enjoyment of the dwellinghouse' — adding a full bathroom or kitchen can push the building outside permitted development, and drainage plus electrics always need building-regulations compliance. In the US, plumbing and electrical work always need permits. Check with your local authority before including either.

For comfortable year-round use, aim for at least 2.1-2.4 m (7-8 ft) internally. Note the code minimums: the IRC requires 7 ft ceilings in habitable rooms (6 ft 8 in minimum for bathrooms), and under UK permitted development the eaves of a garden building can never exceed 2.5 m.

Use whichever your supplier quotes: UK suppliers almost always quote in metres (e.g. 4.0 x 3.0 m), while US builders work in feet. This calculator shows both for every result — recommended area in sq ft and sq m, and the suggested footprint in metres and feet.