Garden Room Cost UK | Price per m² & Size Guide

How to use the garden room cost calculator

Enter the Width and Depth of the room. The calculator works out the floor area.
Pick the Quality of build: basic, standard (insulated, for all-year use) or high spec.
Leave the extras off if your quote is a single price for a finished room. Switch on Upgraded insulation priced on top, Electrics priced on top or Base priced on top only if your quote lists them separately.
Choose Where do you live? to adjust for your area.
Check the range, then tap Add to shopping list to keep it, or Share link to send it to your supplier.

Why use this calculator

The per-m² rates are all-in. They are meant to cover a finished room with a base, insulation and basic electrics, so you don't have to add them up yourself. Check your quote to be sure.

It avoids counting things twice. The extras are switched off by default, and the page warns you if you add them, because most per-m² prices already include them.

It checks itself. For a room near 3 m × 3 m, 4 m × 3 m or 5 m × 4 m, it compares your answer with a published whole-room price.

It shows its working. Under How we worked it out you can see every step with your own numbers.

How we worked it out

Your numbers, step by step. This updates as you change the calculator.

Size: 4 m × 3 m = 12 m².
A standard garden room costs £1,500 to £2,000 per m² (typical £1,800), built and fitted. 12 m² × £1,500 to £2,000 = £18,000 to £24,000.
Prices are for the UK average, so no regional adjustment.
Add it up: low £18,000, typical £21,600, high £24,000.
Sense check: one guide prices a 4 m × 3 m garden room at £18,000 to £28,000 all in (typical £23,000). Our room-only typical is £21,600 at UK average prices.

How we estimate the cost

We multiply the floor area (width × depth) by a price per m² for the build quality you chose:

Quality	Per m² (low to high)	Typical
Basic	£1,000 to £1,400	£1,200
Standard (insulated, all-year use)	£1,500 to £2,000	£1,800
High spec	£2,000 to £2,500	£2,250

These per-m² rates are all-in. They are for a standalone garden room, supplied and built, and they typically include foundations, insulation and basic electrics. Check your quote to be sure. The basic rate comes from one source, and the high-spec rate from two.

If your quote lists extras separately, you can add them:

Upgraded insulation: £1,500 to £4,000 (typical £2,750) for floor, walls and roof.
Electrics: £1,000 to £2,500 (typical £1,500) for a consumer unit, sockets and lighting. The cable run from the house is often extra.
Base: ground screws at £30 to £50 per m² (typical £40) or a concrete slab at £80 to £120 per m² (typical £100).

Your region multiplier then applies to every line. For rooms close to 3 m × 3 m, 4 m × 3 m or 5 m × 4 m, we also show a published whole-room price as a sense check: £12,000 to £20,000, £18,000 to £28,000 and £30,000 to £45,000.

What’s included

A finished, standalone room with a base, insulation and basic electrics, at the per-m² rate.
Any extras you switch on.
Not included: plumbing, a shower or toilet, the cable run from the house, planning or building regulations fees, and VAT (our sources disagree on whether their prices include it).

What changes the price

The size. Our sources only price garden rooms up to about 5 m × 4 m. Larger rooms can cost more per m².
The build quality. Cladding, glazing and internal finishes move the price a lot.
The base. Ground screws and a slab cost different amounts.
Your area. We use London ×1.25, South East ×1.15, Scotland ×0.93, Wales ×0.92, the North ×0.92 and Northern Ireland ×0.88.
The supplier. Two firms can quote very different prices for a similar room.

Tips

Get at least three quotes, and ask each to list what's included: base, insulation, electrics, flooring, internal finish and delivery.
Check the base. A ground screw base is cheaper than a concrete slab, and the type can affect your price, so ask which one is in the quote.
Ask about the cable run from the house. It is often left out of the price and can add £400 to £1,500.
Plumbing, a shower or a toilet are not in this calculator. If you want them, ask each supplier to price them as a separate line.
Garden rooms can fall under planning and building rules depending on their size, height and use. Check with your council before you order.
Got a quote already? Put it through the quote checker to see how it compares.

FAQs

How much does a garden room cost in the UK?

A standard 4 m × 3 m garden room costs about £18,000 to £24,000 in our rates, with a typical price of £21,600. One guide puts a finished room of that size at £18,000 to £28,000. The same guide puts a 3 m × 3 m room at £12,000 to £20,000 and a 5 m × 4 m room at £30,000 to £45,000.

How much does an insulated garden room cost?

About £1,500 to £2,000 per m², typically £1,800. That's our standard level, which is insulated for all-year use. A 12 m² room comes to about £18,000 to £24,000. If your quote prices upgraded insulation separately, add about £1,500 to £4,000.

How much does a garden room cost per m²?

Basic is about £1,000 to £1,400 per m², standard about £1,500 to £2,000 and high spec about £2,000 to £2,500. These rates cover a finished room including the base, insulation and basic electrics. Check what is in your quote.

How much does the base for a garden room cost?

Ground screws are about £30 to £50 per m² and a concrete slab about £80 to £120 per m². For a 12 m² room that's roughly £360 to £600 for screws or £960 to £1,440 for a slab. Most per-m² prices already include the base.

How much does a garden room with a shower and toilet cost?

We don't price plumbing, a shower or a toilet, because we didn't find a reliable figure. Ask each supplier to price them as a separate line, and check what the drainage and water supply will involve.

Do I need planning permission or Building Regulations approval for a garden room?

It depends on the size, the height, where it sits in the garden and how you use it, so check with your council. Some garden rooms need neither and some need one or both.

Is VAT charged on a garden room?

Check each quote. Our sources disagree on whether their garden room prices include VAT, so ask your supplier to say clearly whether VAT is in the price.