Getting your bathroom measurements right before you buy anything is the single most important step in a bathroom renovation. Order a bath that's 50mm too long, or a vanity unit that blocks the door swing, and the whole room will be compromised. This guide covers exactly how to measure every key fixture in your bathroom, what to account for beyond the obvious dimensions, and how to avoid the most common planning mistakes.
Why is it important to measure your bathroom?
Unlike a living room, where furniture can be shuffled around, every fixture in a bathroom connects to plumbing, bolts to walls, or sits above drainage. Getting your bathroom dimensions wrong doesn't just mean returning a product. It can mean rerouting pipes or replastering walls. Accurate measurements give you a realistic picture of what will fit and what won't, long before anything is ordered. They also help your plumber or installer quote accurately, preventing expensive surprises mid-project.
Measuring your bathroom dimensions
Start here, before you think about individual fixtures. Measure the full length and width of the room at floor level. Don't assume the room is a perfect rectangle. Many UK bathrooms have slight variations between walls, so measure both the length and width at two points near each end of the wall, and use the smaller figure to be safe.
Record the ceiling height too. This matters for tall storage units, heated towel rails, and any wall-hung fixtures that need to clear door frames or light fittings.
Sketch the room on paper as you go, noting every measurement. A rough plan, even a hand-drawn one, is far more useful than a list of numbers.
Measuring your door and window placements
Mark the position of every door and window on your sketch. For doors, measure the width of the door itself and note which direction it opens. A door that swings inward will eat into your usable floor space and can rule out certain fixture positions entirely.
For windows, note the height of the sill from the floor. This affects where a bath or shower enclosure can sit, and whether a radiator or vanity unit will obstruct the opening. Also note any window reveals or recesses, as these can sometimes be used to house shelving or a recessed cabinet.
How to measure for a toilet
Standard close-coupled toilets typically measure between 680mm and 800mm in length (projection from the wall), 360mm to 400mm wide, and sit at a rim height of around 400mm. Wall-hung toilets project less from the wall (usually 500mm to 560mm) because the cistern is concealed inside the wall. When measuring for a toilet, you’ll also need to consider:
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Soil pipe position: This is your starting point. If you're keeping the existing soil pipe, your toilet outlet needs to align with it. Moving a soil pipe is possible, but it adds a significant cost. For a back-to-wall or wall-hung toilet, check whether the existing pipework runs through the floor or the wall before choosing a model.
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Projection from the wall: Measure from the finished wall to the edge of where the pan will sit. You need a minimum of 600mm clear floor space in front of the toilet (we’ll cover more on this in the clearance section).
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Centred waste position: The distance from the wall to the centre of your soil pipe outlet is called the rough-in measurement. Most UK toilets are designed for a 180mm to 230mm rough-in, but always check the exact specifications of the model you're considering.
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Width and side clearance: Allow at least 200mm either side of the toilet pan centre to the nearest wall or obstacle.
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Cistern height: For close-coupled toilets, check that the cistern doesn't block the windowsill or any shelving above.
How to measure for a basin or vanity unit
Basins range from compact 360mm cloakroom models to full 800mm or larger countertop basins. Vanity units are typically 400mm to 1200mm wide, 450mm to 500mm deep, and 820mm to 850mm tall, including the basin. When measuring for a basin, consider:
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Available wall width: Measure the clear wall space where the basin will sit, accounting for any door swings, radiators, or adjacent fixtures that encroach on that area.
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Depth from the wall: Most floor-standing and wall-hung vanity units project 450mm to 500mm from the wall. Confirm you have that depth clear before the nearest obstruction, such as a toilet, bath edge, or door frame.
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Existing plumbing positions: Note where your hot and cold supply pipes and the waste outlet currently sit. Surface-mounted pipework can be chased in, boxed, or rerouted, but it adds cost and work. Ideally, choose a basin or vanity unit that aligns with your existing waste position.
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Wall construction for wall-hung units: Wall-hung vanity units need solid fixing. A masonry wall or a stud wall with correctly positioned noggins will take the load. A standard plasterboard partition without internal support will not. If your wall is hollow, check the unit weight and consider a freestanding vanity unit instead.
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Tap holes: Check whether your basin has one tap hole, two, or three, and buy taps that match. Switching from a one-hole basin to a three-hole model after ordering is not a simple swap.
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Mirror or cabinet above: If you're planning a mirrored cabinet above the basin, measure the height from the basin rim to the ceiling. Most cabinets are 600mm to 700mm tall and sit 150mm to 200mm above the basin rim.
Read our bathroom vanity units height guide for more information on the different measurements.
How to measure for a bath
The most common UK bath sizes run from 1500mm to 1700mm long and 700mm to 750mm wide. Small baths start from 1200mm x 700mm for tight spaces. Freestanding baths need additional clearance on all sides. When measuring a bath, take note of:
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Alcoves or open walls: Most baths sit in an alcove. Measure the alcove width and length precisely. A bath that's even 20mm too wide won't sit properly against the tiling. If you're fitting a bath in an open position, note that you'll need access to at least one side for the waste and overflow connections.
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Bath length and room length: Measure the full length of the wall the bath will run along, then subtract any doorways, radiators, or other fixtures that occupy that wall. This gives you your maximum bath length.
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Waste and overflow position: Standard UK baths have the waste at the tap end. Measure where your existing waste outlet sits in the floor or wall and choose a bath accordingly. Left-hand and right-hand overflow options exist for corner baths, so check the spec carefully.
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Floor strength and bath weight: A standard acrylic bath filled with water can weigh upwards of 250kg. Cast iron and steel baths are significantly heavier. If you're replacing a bath on an upper floor, check that the floor joists can take the load.
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Bath panel clearance: If you're fitting bath panels, allow for the panel thickness (usually 15mm to 20mm) in your overall measurements.
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Shower over bath: If you're planning to install a shower bath, check the ceiling height (minimum 2000mm is recommended above the showerhead position) and the wall space for a bath shower screen.
Our standard bath size guide covers the different dimensions in more detail to help you choose the right design for your bathroom size.
How to measure for a shower enclosure
Shower enclosures are sold by their tray footprint. Common sizes are 800mm x 800mm, 900mm x 900mm (square), and 1200mm x 800mm or 1200mm x 900mm (rectangular). Walk-in showers can run from 1000mm up to fully custom widths. Here’s what you will need to measure when deciding which shower enclosure will best fit your space:
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Available floor space: Measure the width and depth of the area you're allocating to the shower. Don't forget to account for the wall thickness of any studwork partition if you're creating a dedicated shower area.
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Door swing direction: A hinged or pivot door needs clear space in front of it to open. Measure this carefully in relation to the toilet, basin, and the room door. If space is tight, a sliding door or bifold door avoids the problem.
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Wall squareness: This is the step most people miss. Use a spirit level and a set square to check whether your walls meet at 90 degrees. A quadrant enclosure relies on a true corner. If your walls are out by more than 5 to 10mm, you'll need adjustable profiles or a different enclosure type.
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Ceiling height: Standard enclosures are typically 1850mm to 2000mm tall. Measure your ceiling height and confirm the enclosure fits without modification. Sloped ceilings in loft conversions need particular attention here.
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Drainage position: The waste outlet position in your floor determines which shower tray orientations will work. Rectangle trays can sometimes be rotated 90 degrees to align with an existing waste, but check the waste position on the tray spec first.
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Shower valve position: The thermostatic shower valve sits on the wall inside the enclosure. Allow for the valve position when choosing the enclosure width, and confirm there's enough wall space for a shower head and riser rail at a comfortable height.
For more information on types and sizing, read our ultimate guide to shower enclosures.
How to measure for bathroom furniture
Bathroom furniture includes storage cabinets, tallboys, shelving units, and fitted furniture runs. Getting this right is less about plumbing and more about spatial planning. Here are some key measurements to note when planning for bathroom furniture:
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Wall-to-wall width for fitted runs: Fitted bathroom furniture is designed to span a specific wall. Measure the wall width at both floor level and at the height the units will sit, as older properties can have walls that taper. Use the smaller measurement.
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Floor-to-ceiling height for tall units: Measure from the finished floor to the underside of any coving or ceiling obstruction, not just to the ceiling itself.
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Depth and door clearance: Most bathroom wall cabinets project 120mm to 150mm from the wall, and floor-standing units are typically 300mm to 450mm deep. In a narrow bathroom, a deep unit opposite the toilet or shower door can create an obstruction. Measure the gap between the unit face and the nearest opposite fixture.
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Pipe and socket positions: Mark any pipes, sockets, or light switches that fall on the wall where furniture will be positioned. These may need boxing in, relocating, or working around.
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Weight and wall type: Wall-hung cabinets need to be fixed to a solid material. For hollow stud walls, use a stud finder to locate the timber and fix directly into it, or use cavity fixings rated for the cabinet's weight.
For more storage ideas, read our guide to small bathroom storage ideas.
Measuring for walkways and clearance zones
Individual fixture measurements only tell part of the story. Fixtures need to work together in the same space. The general guidance for a comfortable bathroom is a minimum of 600mm clear floor space in front of every fixture you actively use. In small bathrooms, some of these zones can overlap slightly, but 400mm is the realistic minimum before a space becomes genuinely difficult to use.
Door swings need their own clear zone. A standard 762mm door swings a 762mm arc. If a door opens into the bathroom, that arc cannot be obstructed by a toilet, basin, or towel rail.
Allow 700mm to 800mm between facing fixtures (for example, a vanity unit on one wall and a toilet or bath on the opposite wall). Less than this, and the room will feel and function like a corridor.
Tips for measuring your bathroom
Keep these in mind throughout the process:
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Stick to one unit of measurement: Work entirely in millimetres throughout. Mixing metres and centimetres is how mistakes happen.
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Measure twice: Always take each measurement at least twice and confirm that they match before recording them.
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Measure at floor level and mid-wall: Walls in older properties can bow or slope. Take width and depth measurements at floor level, mid-height, and near the ceiling to check for any inconsistencies.
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Note vertical measurements too: The height of existing pipe outlets, waste positions, and soil pipe entries all affect which products will work without rerouting.
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Sketch it out, then try different layouts: A simple floor plan on squared paper (or using a free online bathroom planner) lets you test multiple arrangements before committing. Moving a pencil mark costs nothing. Moving a soil pipe does.
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Account for tiles and finishes: If you're retiling, your finished wall will sit proud of the existing surface by at least 10 to 15mm. Build this into your measurements for recessed cabinets and fitted units.
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Don't forget door and drawer clearances: A vanity unit drawer that runs into the toilet is easy to spot on a plan, but easy to miss when you're just measuring the wall.
Once your measurements are confirmed, the rest of the planning becomes much more straightforward. If you need help at any stage, our team is here to assist. Call us on 0121 753 0700 or visit our Birmingham showroom, where we can guide you through layouts and product choices.