How to Measure a Shower Enclosure Correctly
A shower enclosure can look like a simple purchase until the measurements are a few millimetres out. A door that catches a basin, a panel that will not sit against an uneven wall, or an enclosure that does not match the tray can delay the whole bathroom project. Knowing how to measure shower enclosure spaces properly means you can order with confidence and choose from the right sizes first time.
The key is to measure the finished shower area, not the space as it appears before wall panels, tiles or flooring are in place. Keep a note of every dimension, use a reliable steel tape measure, and always check the specification for the particular enclosure before buying. Sizes and adjustment ranges vary between designs and brands.
Start with the shower tray
For most enclosures, the shower tray determines the footprint. Measure the tray's external length and width from edge to edge at its widest points. Do not assume a tray sold as 800 x 800 mm measures exactly 800 mm on every surface - the stated size is the nominal size, while the usable installation area may differ slightly.
Measure along the outer edges where the enclosure frame or glass will sit. If the tray has raised lips, moulded edges or an offset shape, check the product drawing carefully. Quadrant, pentagon and offset quadrant trays need more than one simple width measurement, as their straight wall sections and curved fronts must match the intended enclosure.
If you are replacing an existing enclosure and keeping the tray, measure the tray rather than the old glass. The current enclosure may have an adjustment range that has disguised a slightly undersized or oversized opening.
Measure after finishes where possible
Wall finishes affect the final opening. Tiles, wall panels and tile backer boards can each change the available width, especially in compact bathrooms. Ideally, take final measurements once the tray is in position and finished wall surfaces are complete.
Where this is not possible, allow precisely for the thickness of each finish. Guessing here is a common cause of problems. A pair of wall panels can reduce an opening by more than enough to put it outside an enclosure's adjustment range.
Measure the opening in three places
For a square, rectangular or recessed shower, measure the distance between the finished walls at the bottom, middle and top of the enclosure position. Record all three figures.
Walls are not always perfectly parallel. In older homes particularly, the opening can be wider at the top than at the tray, or vice versa. Use the smallest measurement when assessing whether an enclosure will fit. Most framed enclosures have adjustment in the wall profiles, but that range is designed for small variations, not major discrepancies.
For example, an enclosure with a stated adjustment range of 760-780 mm can suit an opening within those limits. If your wall-to-wall measurements are 758 mm at the bottom, 770 mm halfway up and 777 mm at the top, it is too narrow at the tray level. Choosing a nominal 800 mm enclosure simply because the opening looks close to that size may leave you with no workable adjustment.
Check whether the walls are plumb
An out-of-plumb wall leans slightly in or out rather than running vertically. Check this with a spirit level held against the wall where the enclosure profile will sit. Alternatively, measure the gap between a long straightedge and the wall at several points.
A small amount of variation is often manageable with an adjustable profile. The product information will normally state its adjustment range, though it may not specify every possible wall condition. If a wall is noticeably uneven, choose an enclosure with sufficient profile adjustment rather than relying on sealant to fill a large gap. Sealant finishes the joint - it should not compensate for a poor fit.
Match the enclosure type to the available space
The measurement process changes slightly depending on the enclosure style. The tray footprint still comes first, but door movement and fixed-panel positions are just as important.
Sliding and bifold doors
Sliding doors are a practical option where there is limited room in front of the shower, as the door panels move within the enclosure rather than swinging outwards. Measure the tray and wall opening as normal, then check the door's stated access width. A wide enclosure does not always provide the widest entry, because fixed glass and overlapping panels reduce the opening.
Bifold doors also save floor space, but make sure the folded door will clear nearby furniture, radiators and towel rails. Note the direction in which handles and panels move, not just the overall enclosure size.
Pivot and hinged doors
A pivot or hinged shower door needs clear space to open. Measure from the hinge side to the nearest obstruction, including a basin, toilet, radiator, vanity unit or wall. Remember that skirting, pipe boxing and protruding handles can all affect clearance.
Check the product's door opening radius and whether it opens outward, inward or both. An outward-opening door can be useful for access and cleaning, but it needs a clear bathroom floor. In a narrow room, a slider or bifold design may be the better use of space.
Walk-in screens and fixed panels
For a walk-in shower, measure the length of the tray edge that will be screened, then consider the open entry area. A longer panel offers more splash protection, while a larger gap creates easier access. The right balance depends on shower position, shower head type and how exposed the bathroom is to spray.
Check the panel height as well as its width. A fixed screen should suit both the room's proportions and the height of the shower head. If you are pairing a panel with a return screen or a stabilising bar, allow for those components in the overall layout.
Quadrant and offset quadrant enclosures
Quadrant enclosures are designed for corner trays with a curved front, making them a popular choice where floor space is tight. Measure both straight sides of the tray and confirm whether it is a standard quadrant or an offset version. Offset quadrant trays are longer on one side, so handedness matters.
Stand facing the shower from the room and identify whether the longer side or door position is on the left or right, using the manufacturer's diagram. Do not rely on a product image alone, as images can be reversed. Selecting the wrong handing can put the door opening against a wall or bathroom fixture.
Allow for tray position and room obstacles
A shower tray must sit level, but the room itself may have awkward features around it. Measure and note pipe boxing, window ledges, sloping ceilings, boxed-in cisterns, towel rails and fitted furniture near the enclosure. These details may not affect the tray dimensions, but they can prevent a door from opening fully or interfere with a stabilising bar.
Also check the ceiling height where tall panels or a shower head will be positioned. This is particularly relevant in loft conversions, where sloping ceilings can reduce usable shower space quickly.
If the shower tray is set into an alcove, take measurements from the points where the wall profiles will actually meet the walls. Decorative tile trims and uneven tile edges can affect this line. It is worth measuring twice before placing an order, especially when a recess has little adjustment available.
Read enclosure sizes as ranges, not fixed figures
A stated 900 mm shower enclosure is usually intended for a 900 mm tray, but it is not necessarily 900 mm wide once assembled. Framed enclosures commonly have a minimum and maximum adjustment range. Frameless or semi-frameless designs may have less tolerance and can require more accurate wall conditions.
Always compare your smallest opening measurement with the product's adjustment range. Then confirm that the tray size, enclosure style and door configuration all correspond. This is more reliable than buying solely by the nominal size in the product name.
Do not forget that shower doors may have an adjustment range separate from a matching side panel. For a rectangular enclosure made from two components, check both measurements individually. A 760 mm door and 900 mm side panel should each be suitable for their respective tray edges.
Keep a simple measurement record
Before choosing an enclosure, write down the tray length and width, the opening measurements at bottom, middle and top, the wall condition, and the door clearance available. Add a quick sketch showing nearby fixtures and which way the door needs to open. It takes only a few minutes and makes comparing products much easier.
A few accurate measurements are far more valuable than choosing the closest-looking size. With the tray, finished wall opening and access space confirmed, you can select a shower enclosure that suits your room, your layout and the way the bathroom will be used for years to come.
Ready to choose the right enclosure?
Browse the full shower enclosures collection at Brand New Bathrooms, including sliding, pivot, hinged and bifold doors, quadrant and offset quadrant designs, and walk-in panels in framed and frameless styles. If your measurements fall between sizes, or a wall is out of plumb, our team is always happy to talk through adjustment ranges and fit before you buy.