Bathroom planning is one number repeated: every fixture needs the floor in front of it that a person standing there occupies. For a toilet that is 600 mm of depth and 400 mm from the pan centreline to a wall or fixture on each side. For a basin it is 600 mm in front. For a shower 600 mm to step out and dry, and for a bath 700 mm along its open side. Those zones may overlap each other — you only use one at a time — but none of them may be occupied by something built in.
The clearances
| Fixture | Clear in front | To the side |
|---|---|---|
| Toilet (WC pan) | 600 mm | 400 mm from centreline each side (200 mm off the pan) |
| Basin | 600 mm (700 comfortable) | 450 mm from centreline; two basins 900 mm apart |
| Shower | 600 mm outside the tray | — |
| Bath | 700 mm along the open long side | — |
| Bidet | 600 mm | 400 mm from centreline |
The fixtures themselves
Gridsnap’s catalog defaults, which are ordinary product sizes:
| Fixture | Footprint |
|---|---|
| Toilet | 400 × 700 mm |
| Basin | 550 × 450 mm |
| Basin (in counter) / Basin (on counter) | 900 × 500 mm |
| Shower | 900 × 900 mm |
| Bathtub | 1700 × 750 mm |
Add the clearance to the depth and you get the room. A 700 mm toilet plus 600 mm in front is 1.3 m; a 900 mm shower plus 600 mm is 1.5 m. That is why Gridsnap’s minimum bathroom is 2.0 m² and 1.2 m wide, and its minimum separate WC is 1.0 m² and 850 mm wide — see minimum room sizes.
Planning rules worth following
- Put the shower in a corner. It is the one fixture that gains nothing from a free side, so it should absorb the awkward corner and leave the good wall for the basin.
- Toilet in a corner too, away from the shower. Its clearance zone is the one that can least afford to be crossed by a route.
- The door must not swing onto the toilet. Hinge it the other way, or use a sliding door. Gridsnap flags this one.
- Wet-room partitions run thick. Allow 150–200 mm behind a WC for the soil pipe, or a duct wall, and remember that comes out of the room.
- Twin basins need 900 mm each. Two 550 mm basins on a 1.2 m counter share one puddle and one elbow.
- A window over a bath is fine, over a WC less so — see window sill heights; a 1400 mm sill is the wet-room convention.
Gridsnap checks this automatically
The rule is fixture-clearance, part of the Pro plan check, and it
covers two of the fixtures above:
- Toilet. A wall or another fixture in the strip in front of the pan, or within the side zone, produces “less than 500 mm clear in front of the toilet; toilet centre should be ~400 mm from side walls and fixtures.”
- Basin (all three variants). The front strip is checked to a depth of 550 mm, and separately the middle of the front is measured for real standing depth — “only ~350 mm in front of the basin — keep ~550 mm clear to stand and open it.” The second test exists because a wall a little way in front of a fixture blocks only a fraction of the strip’s area and still leaves nowhere to stand.
The toilet threshold is 500 mm, not the 600 mm this page recommends. That is a known gap between Gridsnap’s constant and its own drafting standard, not a different opinion about toilets. A pan with 550 mm in front of it will pass the plan check and should still be moved.
Two other Pro rules do bathroom work: blocks-door covers a door swinging
onto a fixture, and no-route requires a walkable route to reach the
working face of the toilet, basin, shower and bath.
What this doesn’t do
- There is no clearance rule for a shower or a bath. Circulation must reach them, but nothing measures the 600 mm and 700 mm you need to step out into. Check those by eye or by drawing a dimension.
- No accessible-bathroom check. Turning circles, transfer space beside a WC, grab-rail zones and level thresholds are not modelled at all.
- No plumbing. Soil-pipe runs, falls, stack positions and duct space are outside what Gridsnap knows — which is exactly why the wall behind a WC needs more thickness than the plan suggests.
- No ventilation check. Whether a windowless bathroom has mechanical extract is not tested.