For most small cloakrooms and en-suites, a 900mm toilet and sink unit is the one to go for. It puts a compact basin, a concealed cistern and a back-to-wall toilet along a single 900mm run of wall, so you hide all the pipework and cabling behind one tidy front. If you have got a bit more wall to play with, 1100mm and 1150mm units give you a wider basin and more storage. This guide is about one thing only: working out which width actually fits your wall, so you order once and it goes in without a fight.

Choosing the unit itself, the pan style, the flush and so on, is a separate job. We cover that in the guide to choosing a toilet. Here we stick to the tape measure.

• The sizes at a glance: 900, 950, 1100 and 1150mm
• How to measure your wall properly
• 900mm vs 1100mm: what the extra 200mm buys you
• The smallest units, and cloakroom fit
• Left-hand vs right-hand and soil pipe position
• FAQ

The sizes at a glance: 900, 950, 1100 and 1150mm

Combination units are sold by the total width of the run, wall to wall. That number, 900mm or 1100mm, is the overall footprint you need to leave clear along the wall. Everything sits inside it: the basin and vanity cupboard on one side, the concealed cistern unit and back-to-wall pan on the other.

The four widths below are the ones we stock and the ones people actually search for. The projection is how far the unit sticks out from the wall into the room, which matters as much as the width in a tight space. The prices are the cheapest we are selling each at right now, not a crossed-out ticket price.

A couple of things to notice before you fall for the lowest number. Price does not climb neatly with width here, because finish and range matter as much as size. The gloss white Litchfield 1150mm combination set from £229 is our cheapest of the four and also the widest, while the anthracite Amy 900mm combination unit from £349 costs more in the smallest width. It is built on an 18mm solid carcass with a one-piece polymarble countertop and soft-close door hinges, so you are paying for the matt anthracite finish and the build, not just the millimetres.

How to measure your wall properly

This is where most orders go wrong. The width on the box is the outside edge of the whole unit, so you need a clear run of wall at least that long with nothing in the way. Measure the wall, then knock off anything that eats into it before you decide.

Take these four measurements and write them down. Do not eyeball any of them.

1. Usable wall length. Skirting to skirting, or into the corner if it butts up to a return wall. A 900mm unit needs 900mm of clear wall, and ideally a few mm spare so you are not forcing it in.
2. Projection into the room. How far the unit sticks out from the wall, and whether that leaves you enough clear floor to stand and use the loo comfortably. It varies by range: the slimmer Litchfield sets project 500mm, while the Amy 900 sits deeper at 700mm. Tight cloakrooms live or die on this number.
3. Door swing. Open your bathroom door and see where it lands. If it clips the unit or the basin, you either need a narrower unit, the door rehung, or a change to a sliding door.
4. Soil pipe position. Note whether your waste exits the wall on the left, the right, or straight out the back behind the pan. This decides which way round the unit has to sit, which we come back to below.

One more, if you are fitting into an alcove or between two walls: measure the gap at floor level and again at the height the worktop will sit, because older walls are rarely square. Go off the smaller of the two. If you are doing the whole room at once, our guide to designing a small bathroom walks through how these units fit around a shower and door.

Two mistakes come up again and again, so learn from other people’s grief. The first is measuring to the wall but forgetting the skirting board, which can steal 15mm to 20mm off each end and leave a 900mm unit that will not quite go in. The second is ignoring the tap. A tall or angled tap can foul a window sill or a mirror above the basin, so if either is close, check the clearance before the plumbing goes live. Neither costs you anything to get right at the tape-measure stage, and both are miserable to fix afterwards.

900mm vs 1100mm: what the extra 200mm buys you

Jumping from 900mm to 1100mm adds 200mm of width, and almost all of it goes into the vanity side rather than the toilet. The pan and cistern take up roughly the same room whatever the total width, so the extra 200mm becomes a wider basin and a bigger cupboard underneath it.

In plain terms, here is what the extra width actually gets you:

• A wider basin you can properly use, rather than a compact hand-rinse bowl.
• More cupboard storage for cleaning bits, spare rolls and the clutter that otherwise ends up on the cistern lid.
• A bit of worktop beside the basin for soap, a plant, whatever, instead of nothing.

So the rule is simple. If it is a downstairs loo or a squeezed en-suite, 900mm is plenty and the smaller footprint is worth more than the extra storage. If it is a main bathroom or a guest en-suite where people actually wash properly, spend the 200mm. The gloss white Amy 1100mm combination unit from £349 is the same range as the 900mm, so you can match finishes if you are kitting out more than one room.

At the same 1100mm width you will also see the anthracite Empire unit. Ranges vary in what comes in the box, some are the furniture and cistern housing with the pan bought separately, so before you compare on price alone, check the specification on the product page and note whether a pan is included. The width you need to leave clear on the wall is the same either way.

The smallest units, and cloakroom fit

900mm is the smallest full combination unit we would put in a room someone has to use daily, and it is the honest floor for a comfortable cloakroom. You can find narrower single vanity units, but once you combine a basin, cistern and pan into one run, 900mm is about as tight as it goes before the toilet feels cramped. That is why “900mm cloakroom toilet and sink unit” is the search we see most.

If the total width is your only worry and budget is tight, the Litchfield 950mm combination set from £249 gives you the concealed cistern look for less, at just 50mm more than the 900mm units. For a very small cloakroom where even a combination unit is a stretch, a separate compact basin can work better than a combined run, and our cloakroom vanities and basins cover that route. There is a full cloakroom vanity units buying guide if you want to weigh the two up.

If you are trying to claw back every millimetre across the whole room, it is worth thinking about the layout as a set rather than piece by piece. Matching space-saving bathroom suites are designed so the basin, toilet and any storage line up on a common depth, which stops the wasted gaps you get from mixing ranges.

Left-hand vs right-hand and soil pipe position

Combination units have a basin on one side and the toilet on the other, so which way round they sit matters. Which side your basin lands on comes down to two things: where your soil pipe exits, and which way your door opens. Get these the wrong way round and you either block the door or end up with an awkward reach to the loo.

Back-to-wall pans, which is what these units use, waste straight out the back into the concealed cistern housing, so a rear soil exit is the easy case. If your waste currently runs off to the left or the right, a plumber can usually adapt it, but it is worth checking before you commit to a layout. Some ranges make this easier than others: both the Litchfield 950mm and 1150mm sets are designed for flexible left or right installation, so the basin can sit on whichever side suits your room. Always confirm the handing shown on the specific product page you are buying, because not every unit and colour is offered in both set-ups.

FAQ

What is the smallest toilet and sink unit?

For a proper combined unit with a basin, concealed cistern and back-to-wall pan, 900mm is the smallest we would fit in a room used every day. Narrower options exist as separate basins, but a combined run below 900mm starts to feel cramped around the toilet. A 900mm unit is the sweet spot for most cloakrooms.

What size is a 900mm cloakroom toilet and sink unit?

The 900mm refers to the total width of the run, wall to wall, taking in the basin and cupboard on one side and the cistern housing and pan on the other. You need a clear 900mm of wall, plus room for the unit to project into the floor space and for the door to open. Measure all three before you order.

Do these units come in grey as well as white?

Yes. The Litchfield sets come in gloss white, while the Amy 900mm is finished in matt anthracite grey, which is why “grey toilet and sink unit” is a common search. The colour does not change the width or the fit, only the look, so measure first and pick the finish second.

Is a 900mm or 1100mm unit better for a small bathroom?

In a genuinely small room, 900mm. The smaller footprint frees up floor space and the toilet still has room around it. Step up to 1100mm only when you have the wall length and want a bigger basin and more storage rather than just squeezing everything in.

You might also find these useful. If you are still deciding on the toilet itself, start with our guide to choosing a toilet. Planning the whole room around one of these units is covered in how to design a small bathroom, and if it is a downstairs loo you are fitting out, the cloakroom vanity units buying guide is the one to read next. When you are ready to browse, the full range sits in our bathroom furniture sets.