- What actually decides a bathroom layout
- How much space each fixture needs to be usable
- Why moving the toilet costs more than moving anything else
- What the cheapest bathroom layout to build looks like
- How to lay out a small bathroom
- Where the layout gets locked in the renovation sequence
- Frequently asked questions
Most bathroom layouts are designed the wrong way around. The homeowner starts with where the freestanding bath would look best, where the vanity should sit under the window, where the shower should catch the morning light. Then the plumber arrives, looks at the existing pipework, and explains what that layout will actually cost. A bathroom layout is not an arrangement of fixtures by taste. It is set by where the water already leaves the room.
The two fixed points in any bathroom layout are the soil stack, where the toilet waste joins the building's drainage, and the floor waste, where the shower and floor drain away. Every fixture you can place freely, and every fixture you cannot, is decided by its distance from those two points. The homeowner who designs the bathroom layout around the existing services builds a cheaper bathroom that works. The one who designs around the magazine photo pays to move the plumbing.
A bathroom layout is not where the fixtures look best. It is built around where the water already leaves the room.
This guide covers what really sets a bathroom layout, how much space each fixture needs, why the toilet is the most expensive thing to move, and where the layout has to be locked in the renovation sequence.
What actually decides a bathroom layout
Plumbing decides it. A bathroom is the most service-dense room in the house: water supply, drainage on a fall, waterproofing, ventilation, and electrical all share a space that is often under four square metres. The layout that ignores how those services run is the layout that generates variations.
The soil stack is the anchor. The toilet has to connect to it, and because soil pipe runs on a gradient and is large in diameter, the toilet wants to stay close to where the stack already is. The floor waste is the second anchor: the shower and the bathroom floor drain to it, and the whole floor has to be graded so water runs toward it. Work outward from those two fixed points and the layout almost designs itself. Ignore them and every fixture becomes a plumbing relocation. The order each trade then works in is set out in the guide to managing trades on a bathroom renovation.
How much space each fixture needs to be usable
A layout that fits on paper can still fail in use if the clearances are wrong. Australian bathroom designers work to a consistent set of activity-space figures, and they are the difference between a bathroom that feels generous and one where the door hits the vanity.
- Toilet. Allow at least 450mm from the centre of the pan to any wall or fixture on each side, giving a 900mm-wide zone, plus 600mm of clear space in front of the pan.
- Vanity and basin. Allow at least 100mm clear on each side of the basin and around 700mm of activity space in front so a person can stand and lean in comfortably.
- Shower. A shower wants to be 900mm by 900mm at the absolute minimum, with 1,000mm by 1,000mm far more comfortable and easier to keep water contained.
- Door and circulation. A standard 820mm door needs its swing kept clear of every fixture, and a walkway through the room wants 700mm to 1,000mm of clear floor.
- Bath. A standard inset bath is around 1,700mm long; a freestanding bath needs clear space around it on at least two sides to read as freestanding rather than wedged.
These figures are not regulations, but they are what separates a layout that works from one that technically holds the fixtures. Draw the room to scale, place the clearances as blocked-out zones rather than the fixtures themselves, and the layout either fits or it does not.
Cost the layout before you commit to it
The free Renovation Cost Calculator gives you a trade-by-trade estimate in under 5 minutes — before your first trade conversation. It shows what the plumbing, waterproofing, and tiling actually cost, so a layout that moves fixtures is priced honestly before it is drawn.
Why moving the toilet costs more than moving anything else
Of every fixture in a bathroom, the toilet is the most expensive to relocate, and the reason is the soil pipe. Toilet waste runs through a 100mm pipe that has to maintain a constant fall to reach the soil stack. Move the toilet a metre and that pipe has to be re-routed under the floor, re-graded, and reconnected, work governed by AS/NZS 3500 and done by a licensed plumber. On a ground-floor slab, that can mean cutting the concrete.
A basin or shower is far more forgiving. They use smaller supply and waste pipes that are easier to extend, so moving them a short distance is a modest cost. The hierarchy is worth holding onto when sketching options: the toilet is the most expensive to move, then the shower, then the bath, then the vanity. A layout that keeps the toilet on or near the existing soil stack and shuffles only the cheaper fixtures is a layout that stays close to budget. This is one of the single biggest drivers of the gap explored in the bathroom renovation cost guide.
If the budget is tight, keep the toilet where the soil stack already is. It is the most expensive fixture to move, because its waste pipe has to be re-graded and re-routed, often through a concrete slab.
Move the cheap fixtures, anchor the expensive one. A layout that relocates the vanity and shower but leaves the toilet in place can cost a fraction of one that moves all three.
What the cheapest bathroom layout to build looks like
The cheapest bathroom layout to build is the one that groups the plumbed fixtures on a single wall, sometimes called a wet wall. When the toilet, basin, and shower all draw from and drain to services running through one wall, the plumber runs one set of pipes rather than three, and the cost of the rough-in drops accordingly.
A like-for-like layout, where every fixture stays roughly where it already is, is cheaper again, because it reuses the existing pipework almost entirely. The most expensive layout is the full reconfiguration, where the toilet, shower, and vanity all move to new walls and the entire room is re-plumbed. The difference between these on a standard bathroom is not small; the re-plumb can add several thousand dollars before a single tile is laid. None of this means a homeowner should never move a fixture, only that moving one should be a deliberate decision with a known cost, not a default of the design.
How to lay out a small bathroom
A small bathroom is a layout problem before it is a style problem, and the rules tighten as the room shrinks. In a room around 2,000mm by 2,000mm, a three-piece layout of toilet, basin, and shower fits only if the clearances are respected and the fixtures are chosen to suit the space.
The moves that make a small bathroom work are consistent: place the three fixtures along one or two walls to keep the plumbing grouped, use a shower in place of a bath to reclaim around 1,700mm of length, hang the vanity off the wall so the floor reads as continuous, and consider a cavity sliding door or an outward-opening door so no swing is lost inside the room. A corner shower can recover space a square shower cannot. The full set of small-space decisions is covered in the small bathroom renovation guide, but the layout principle is the same as in a large room: anchor to the services, respect the clearances, and move only what is worth moving.
Where the layout gets locked in the renovation sequence
Within The 12-Phase System, the bathroom layout is finalised at phase three — design finalisation and specification — and it becomes physically permanent at phase eight, rough-in. Once the plumber has set the pipework and the waterproofer has applied the membrane to AS 3740, the layout is fixed. Tiles go over the membrane, and changing a fixture position after that point means stripping waterproofing that has already been signed off.
This is why the layout cannot be left to be resolved on site. The sequence runs in one direction:
- Draw the room to scale. Mark the existing soil stack and floor waste first, because they are the two points the layout is built around.
- Block out the clearances. Place the activity zones, not just the fixtures, so the layout is tested for use before it is committed.
- Decide what moves. Choose deliberately which fixtures relocate, knowing the toilet is the most expensive, and price each move.
- Lock the plan before rough-in. Issue the final layout to the plumber and waterproofer so the pipework and membrane are set to the agreed positions.
- Hold the layout through waterproofing. Once the membrane is down and signed off, treat the layout as final, because it now is.
A homeowner who completes those five steps in order arrives at rough-in with a layout the trades can build straight from. One who leaves it open discovers the cost of a moved fixture at the worst possible moment, after the waterproofing is already down. The full pre-rough-in sequence is in the bathroom renovation planning checklist.
Plan the whole bathroom, not just the layout
The Bathroom Renovation Blueprint carries the full specification sequence — layout, clearances, fixture positions, waterproofing sign-off, and the order they have to be locked in — so the room is resolved on paper before the plumber arrives.
If the cost baseline is the right first step, use the free Renovation Cost Calculator — a trade-by-trade estimate for the specific bathroom, in under 5 minutes, before any trade has quoted.
Frequently asked questions
What decides a bathroom layout?
The plumbing decides it, specifically the soil stack where the toilet waste connects and the floor waste where the shower and floor drain. Those two points are fixed and large to move, so the most cost-effective layout is built outward from them. Fixtures placed close to the existing services are cheap to install; fixtures placed far from them require the pipework to be relocated.
How much space does a toilet need on each side?
Allow at least 450mm from the centre of the toilet pan to any wall or fixture on each side, which gives a 900mm-wide zone, plus around 600mm of clear space in front of the pan. Less than that and the toilet feels cramped and is harder to clean around. These are design figures used by Australian bathroom designers rather than strict regulations.
Why is moving a toilet so expensive?
Because the toilet drains through a 100mm soil pipe that has to maintain a constant fall to reach the soil stack. Relocating the toilet means re-routing and re-grading that pipe under the floor, and on a ground-floor concrete slab it can require cutting the slab. Basins and showers use smaller, more forgiving pipes, so they are far cheaper to move.
What is the cheapest bathroom layout?
The cheapest layout groups the toilet, basin, and shower on a single wet wall so the plumber runs one set of services, or keeps every fixture in its existing position to reuse the current pipework. The most expensive layout moves all three plumbed fixtures to new walls, which requires the whole room to be re-plumbed and can add several thousand dollars before tiling.
Can a small bathroom fit a toilet, basin, and shower?
Yes. A three-piece layout of toilet, basin, and shower fits in a room around 2,000mm by 2,000mm if the clearances are respected. The fixtures are best grouped along one or two walls to keep the plumbing together, a shower replaces a bath to save length, a wall-hung vanity keeps the floor open, and a sliding or outward door avoids losing swing space inside the room.
When in a renovation is the bathroom layout finalised?
The layout is finalised at the design and specification phase and becomes physically permanent at rough-in, once the plumber has set the pipework and the waterproofer has applied the AS 3740 membrane. After waterproofing is signed off, changing a fixture position means stripping a membrane that has already passed inspection, so the layout has to be locked before that point.