The legal minimum bedroom sizes in a licensed HMO are 6.51 square metres for one adult, 10.22 square metres for two adults, and 4.64 square metres for a child under ten, and any floor area under a ceiling height of 1.5 metres does not count towards those figures. Rooms below 4.64 square metres cannot be used for sleeping at all. London boroughs can and do set stricter standards, so this guide covers the rules, the measuring, and how to rescue an undersized layout.
The statutory minimum room sizes
Since October 2018, minimum sleeping room sizes have been a mandatory condition of every HMO licence in England, so they bind every licensed HMO in London automatically.
The figures are precise and worth keeping to hand: 6.51 square metres of usable floor area for one person aged ten or over, 10.22 square metres for two persons aged ten or over, and 4.64 square metres for one child under ten. Any room smaller than 4.64 square metres cannot be used as sleeping accommodation by anyone, of any age.
The licence itself will state how many people may sleep in each room, and the total number of households and occupants the property may house. Letting a 6.2 square metre room to an adult is not a grey area or a negotiation; it is a breach of a licence condition with civil penalties attached.
Note what the figures are: minimums for licensing, not definitions of a good room. A 6.6 square metre adult bedroom is legal and also very hard to let well. The table below sets out the thresholds.
| Occupancy | Minimum usable floor area |
|---|---|
| One person aged 10 or over | 6.51 sqm |
| Two persons aged 10 or over | 10.22 sqm |
| One child under 10 | 4.64 sqm |
| Any room under 4.64 sqm | Cannot be used for sleeping |
How rooms are measured: the 1.5-metre ceiling rule
The minimums refer to usable floor area, and the most important measuring rule is about height: any part of the floor where the ceiling is lower than 1.5 metres does not count towards the figure.
This rule decides the fate of loft rooms across London. A converted loft bedroom that measures a generous 11 square metres wall to wall can shrink to 6 square metres of countable area once the sloping eaves are deducted, taking it below the single-adult threshold even though it feels spacious. Dormers and the flat central section are what save loft rooms, and a measured drawing settles the question before a tenancy or a purchase, not after.
Elsewhere, officers measure the room as the tenant actually uses it. Practice on details such as integral en-suites, deep chimney breasts and entrance lobbies within rooms varies between boroughs, so where a room is close to a threshold, ask the licensing team how they will measure it rather than assuming the answer.
If a room is borderline, treat it as failing until proven otherwise. Rooms that pass by a centimetre on your tape measure have a way of failing by a centimetre on the officer's laser.
Borough standards can be stricter
The national figures are a floor, not a ceiling, and London boroughs are explicitly allowed to apply higher standards through their licensing policies, which many do.
Borough HMO standards commonly expect more space than the statutory minimum where the property lacks a communal living room, on the logic that a bedroom doubling as someone's entire living space needs to be bigger; several London boroughs look for somewhere in the region of 8 to 10 square metres for a single room in that situation. Standards documents also set kitchen sizes relative to occupant numbers, bathroom ratios and storage expectations, all of which interact with how many rooms you can let.
The practical consequence for investors is that the same house can support five lettable rooms under one borough's standards and four under its neighbour's. Before buying or reconfiguring an HMO, download the borough's adopted amenity and space standards and run every room against them, not against the national minimums.
Where a borough standard is genuinely discretionary, officers can and sometimes do exercise judgement, but you want to be the landlord who read the standards and designed to them, not the one discovering them in an inspection report.
What happens when a room is undersized
An undersized room does not usually kill an HMO licence; it shrinks it, and the financial damage arrives through the occupancy schedule.
Where a room falls below 6.51 square metres, the council cannot license it for use by an adult, so the licence will either prohibit its use as sleeping accommodation entirely or, where it exceeds 4.64 square metres, restrict it to a child under ten, which in a shared house means in practice it earns nothing. Where an existing tenant is already in an undersized room, councils can allow a transition period, generally up to 18 months, for the situation to be resolved, but the direction of travel is fixed.
Breaching the condition by continuing to let the room is an offence, with civil penalties of up to £30,000 available per breach, and it undermines the fit and proper person assessment behind every future licence application you make.
The arithmetic is what stings: a room that misses the threshold by half a square metre costs you its entire rent, roughly £8,000–£11,000 a year at London HMO room rates, every year, for as long as the layout stays as it is. That is the number to keep in mind when reading the next section.
Rescuing a layout with partitions and reconfiguration
Undersized rooms are usually a layout problem, not a building problem, and layout problems can be rebuilt.
The most common fix is moving a stud partition to rebalance two adjacent rooms: where a 6.1 square metre box sits beside an 18 square metre double, shifting the wall a few hundred millimetres turns a failing room and an oversized one into two compliant singles, or one strong double and a study. Dead space is the next target: overlong landings, redundant lobbies and oversized built-in cupboards can often be absorbed into an adjacent bedroom to lift it over a threshold.
Sometimes the right answer runs the other way: two hopeless small rooms knocked into one excellent double can out-earn the pair, because a premium double in London lets faster and retains tenants longer than two grudging singles.
Any reconfiguration must keep the rest of the rulebook in view: habitable rooms need adequate ventilation and natural light, escape routes must work from every new room, fire door and alarm coverage must follow the new layout, and acoustic insulation in new partitions is what stops the rescued room generating noise complaints. A moved or new acoustic stud partition typically costs £1,200–£2,500 at 2026 prices, decorated and complete.
Maximising lettable rooms while staying compliant
The profitable version of this exercise starts with a measured survey, not a sledgehammer. Accurate room-by-room dimensions, ceiling heights and the borough's standards side by side reveal exactly which rooms pass, which fail, and which are one moved wall away from passing.
From there it becomes an optimisation problem: which arrangement of partitions yields the most lettable, licensable rooms without breaching space, amenity or fire standards? Often the best answer is not the most rooms but the best mix, since a five-double HMO frequently outperforms a six-room layout containing two reluctant singles, on both rent and voids.
This is the reconfiguration work Apex London does for landlords and letting agents across the capital: measured drawings checked against the borough's standards, partition and door works, the fire doors, alarms and decoration that follow, and the photographic evidence pack for the licensing officer at the end. Done as one project, a typical room-rescue reconfiguration costs £2,000–£6,000 and pays for itself within a year through the recovered rent.
If you are staring at a licensing schedule that has just deleted a bedroom from your HMO, get the property measured before you accept the loss; more layouts can be rescued than landlords expect.
Frequently Asked Questions
What is the minimum bedroom size for an adult in an HMO?
6.51 square metres of usable floor area for one person aged ten or over, and 10.22 square metres for two. These are mandatory HMO licence conditions across England, and floor area under a ceiling height of 1.5 metres does not count towards the figure.
Does floor space under a sloping ceiling count in an HMO room?
Only where the ceiling is at least 1.5 metres high. Anything below that is excluded from the usable floor area, which is why converted loft rooms that measure well wall to wall often fail the 6.51 square metre threshold once the eaves are deducted.
Can my London borough require bigger rooms than the national minimum?
Yes. The statutory figures are a floor, and borough licensing standards are often stricter, commonly expecting around 8 to 10 square metres for a single room where the HMO has no separate communal living room. Always check the borough's adopted HMO standards before letting or reconfiguring.
Can I still use an undersized room as a study or storage?
Yes. The restriction is on use as sleeping accommodation: a room under 6.51 square metres cannot be licensed for an adult, and under 4.64 square metres cannot be slept in by anyone. Letting it informally as a bedroom anyway breaches your licence conditions, with civil penalties of up to £30,000.
How much does it cost to move a partition to fix room sizes?
A moved or new acoustic stud partition costs £1,200–£2,500 at 2026 London prices including decoration, and a full room-rescue reconfiguration with doors, alarms and making good typically runs £2,000–£6,000. Against £8,000–£11,000 a year of recovered room rent, it usually pays back within a year.