The Bathroom Mirror Size Calculator for UK Rooms

Size the mirror from the basin below it and the eye line of the people using it. Not from the wall, and not from the tile pattern. Almost every awkward bathroom mirror in Britain is the result of somebody measuring the available wall and filling it, when the correct reference points are the vanity width and the standing height of the household.

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The working method is short. Match the mirror width to between 70 per cent and 100 per cent of the vanity or basin unit beneath it, set the centre of the glass at roughly 150cm to 165cm above the finished floor, and keep the bottom edge at least 20cm clear of the basin rim or splashback. Everything else, shape, frame, lighting, is a decision that can be made afterwards.

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Key findings at a glance

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• The vanity sets the mirror width. A mirror wider than the unit below it makes the whole wall look unresolved, and a mirror much narrower than 70 per cent of the unit looks stranded.

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• Mirror height is governed by eye line rather than by proportion. The top edge needs to clear the tallest user comfortably, which is why tall narrow mirrors outperform wide shallow ones in family bathrooms.

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• BS 7671, the IET Wiring Regulations, defines bathroom zones and the ingress protection required in each. Zone 1 and zone 2 both call for a minimum of IPX4 for electrical equipment.

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• Electrical installation work in a bathroom falls within the scope of Part P of the Building Regulations, which is the reason an illuminated or demisting mirror is not a straightforward do it yourself fitting.

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• Approved Document F sets an intermittent extract rate of 15 litres per second for a bathroom, and a room that meets it will fog a mirror far less than one that does not.

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• A mirrored cabinet projects from the wall, commonly by 12cm to 15cm, so it should not sit where someone leans in over the basin unless the room can absorb the depth.

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• A mirror hung opposite or perpendicular to the window returns daylight into the room, which is the cheapest change available in a small internal bathroom.

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The three measurements that set the size

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The first is the width of the unit beneath. A basin or vanity gives the mirror its visual base, and the eye reads the two as a single composition. Anything between 70 per cent and 100 per cent of that width sits correctly. Going wider than the unit only works where the mirror runs the full width of the wall and becomes an architectural element rather than a fitting.

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The second is the eye line of the people who will use it. A mirror positioned by centring it on the tiles frequently cuts off the top of a taller person’s head. Setting the centre of the glass at 150cm to 165cm above the finished floor covers most adult households, and in a family bathroom the lower end of that band is the safer choice because children can be raised by a step but adults cannot be shortened.

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The third is clearance. Keep the bottom edge at least 20cm above the basin rim so taps and splashback are not reflected at close range, and leave a margin of at least 5cm to any tile edge or corner. In practice this last measurement is what rules out oversized mirrors in narrow bathrooms, because the wall between a corner and a door architrave is rarely as generous as it looks.

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The calculator

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The table below converts standard UK vanity and basin unit widths into mirror dimensions. All figures are specification led rather than statistical, derived from common modular unit widths and standard mounting heights.

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Vanity or basin width	Mirror width range	Suggested mirror height	Centre of glass above floor
40cm cloakroom unit	30cm to 40cm	50cm to 60cm	150cm to 155cm
50cm unit	35cm to 50cm	60cm to 70cm	150cm to 160cm
60cm unit	45cm to 60cm	70cm to 80cm	155cm to 160cm
80cm unit	55cm to 80cm	70cm to 90cm	155cm to 165cm
100cm unit	70cm to 100cm	80cm to 90cm	155cm to 165cm
120cm unit or twin basins	One mirror of 85cm to 120cm, or two of 45cm to 55cm	80cm to 90cm	155cm to 165cm

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Where two mirrors are used over a double vanity, centre each one on its own basin rather than dividing the wall equally. The basins are the reference, and a symmetrical wall with off centre mirrors reads as an error even when the measurements are precise.

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Zones, ratings and ventilation

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Bathrooms are treated as special locations in electrical terms. BS 7671, the IET Wiring Regulations, divides the room into zones based on proximity to the bath and shower, and sets a minimum ingress protection rating for equipment in each. Zone 1 and zone 2 both require at least IPX4, which is the figure to check on any illuminated, heated or demisting mirror before it is bought.

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The installation itself matters as much as the product. Electrical work in a bathroom falls within the scope of Part P of the Building Regulations, so a mirror requiring a fused spur is a job for a competent electrician rather than a weekend task. A plain unlit mirror avoids all of this, which is a legitimate reason to choose one in a rented property or a room where the wiring is not being altered.

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Ventilation is the overlooked half of the problem. Approved Document F sets an intermittent extract rate of 15 litres per second for a bathroom, and a room achieving that will clear steam quickly enough that fogging is a brief inconvenience rather than a daily one. Where the extract is weak or absent, a demister pad is treating a symptom. Fixing the airflow treats the cause, and it also protects the mirror backing, since prolonged moisture at the edges is what produces the dark spotting that eventually spreads across the silvering.

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Small bathrooms, light and the cabinet decision

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Most British bathrooms are small, frequently built around a 1700mm by 700mm bath, and often internal with no window at all. In those rooms a mirror is doing two jobs: it is a functional surface for washing and shaving, and it is the main tool available for making the space feel less enclosed.

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Position beats size for the second job. A mirror facing the window returns daylight directly into the room, while one on the same wall as the window reflects only the opposite wall. In an internal bathroom, place the mirror where it reflects the door opening or the longest available run, because reflecting depth is what changes the perception of the room. The wider bathroom mirrors UK selection covers both plain and illuminated formats, and the choice between them should follow the wiring position rather than the other way round.

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The cabinet trade off is a real one. A mirrored cabinet stores the items that otherwise clutter the basin, but it projects from the wall, commonly by 12cm to 15cm, and that depth sits exactly where someone leans forward. In a narrow room, wall storage placed elsewhere with a flat mirror over the basin is the more comfortable arrangement, and the units in the bathroom cabinets UK range can take that load away from the mirror wall entirely.

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Where the basin unit is being replaced at the same time, size the two together. The bathroom vanities UK options are supplied in the same modular widths used in the table above, which makes the mirror calculation straightforward before anything is ordered.

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What this means for UK homes

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Work in this order: measure the vanity, calculate the mirror width, set the centre height for the tallest regular user, then check the clearance to corners, architraves and light fittings. Only then choose the shape and frame. Doing it in the reverse order is how a mirror ends up 15cm from a door frame.

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Check the zone before choosing an illuminated model. If the mirror sits within the zones defined by BS 7671, the IP rating is not optional, and the installation needs to comply with Part P. If the room has no suitable spur nearby, a plain mirror with a separate wall light is usually the cheaper and cleaner solution.

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Improve the extract before spending on demisting. A bathroom meeting the 15 litres per second intermittent rate in Approved Document F will hold far less condensation, which protects both the mirror backing and the decoration. Beyond the bathroom itself, the same sizing logic applies to hallway and bedroom glass, and the wall mirrors UK range can be sized against a console or chest using the same 70 to 100 per cent rule.

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Methodology

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This 2026 calculator was compiled by the editorial team at Furniture in Fashion from our editorial assessment as a UK furniture retailer, standard UK vanity and basin unit widths, standard mounting heights and clearances, and named published references including BS 7671 the IET Wiring Regulations, Part P and Approved Document F of the Building Regulations. The ranges given are specification led guidance calculated from those unit widths. The report contains no proprietary sales data and no survey fieldwork, and no national dataset on bathroom mirror sizing exists to draw on.

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Citing this report

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Media and websites may cite this 2026 sizing guidance with credit to Furniture in Fashion and a link back to the report. The figures are practical specifications derived from standard unit widths and published regulatory references, offered as our editorial guidance rather than as research findings. Installation advice should always be checked against current Building Regulations.

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Frequently asked questions

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What size mirror should go above a 60cm vanity?

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A mirror of 45cm to 60cm wide and 70cm to 80cm tall, with the centre of the glass 155cm to 160cm above the finished floor. Keep the bottom edge at least 20cm above the basin rim so the taps are not reflected at close range.

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Should a bathroom mirror be wider than the sink?

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Generally no. Matching 70 per cent to 100 per cent of the unit width below reads correctly. A mirror wider than the vanity only works where it runs the full wall and is treated as a design feature rather than a fitting.

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How high should a bathroom mirror be hung?

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Set the centre of the glass at 150cm to 165cm above the finished floor, choosing the lower end for a family bathroom and the upper end for a household of taller adults. The top edge should clear the tallest regular user comfortably.

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Do I need a special mirror for a bathroom?

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For any mirror with lighting, heating or demisting, yes. BS 7671 sets minimum ingress protection of IPX4 in zones 1 and 2, and the installation is covered by Part P of the Building Regulations. A plain mirror has no such requirement, though a moisture resistant backing will last longer.

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How do I stop a bathroom mirror steaming up?

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Improve the extract first. Approved Document F sets 15 litres per second as the intermittent extract rate for a bathroom, and a room meeting it clears steam quickly. A heated demister pad helps, but it compensates for poor ventilation rather than correcting it.